Control system for work machine, work machine, remote operation system for work machine, and method for controlling work machine

Abstract

This control system for a work machine comprises a controller. The controller acquires an operation signal for switching the traveling direction of the work machine, determines whether the operation signal satisfies an acquired operating condition in a state where the work machine is traveling at a traveling speed equal to or higher than a first speed threshold, and prohibits output of a forward / reverse switching command for switching the traveling direction when it is determined that the operating condition is satisfied.

Description

Work machine control system, work machine, work machine remote operation system, and work machine control method

[0001] The present disclosure relates to a work machine control system, a work machine, a work machine remote operation system, and a work machine control method.

[0002] In the technical field related to work machines, a remote control system for a wheel loader is known, as disclosed in Patent Document 1. In Patent Document 1, the wheel loader has a camera and an antenna. An on-board controller of the wheel loader receives a remote signal from an off-board controller via the antenna. The off-board controller receives a camera image from the camera and displays it on a display.

[0003] EP 3926107

[0004] A work machine operates based on an operation signal from an operating device operated by an operator. For example, if the operating device is operated to suddenly move the work machine in reverse while the work machine is moving forward, a load is placed on the work machine, which may cause deterioration. For example, if the operating device is operated to suddenly move the work machine uphill while the work machine is moving downhill, a load is placed on the work machine, which may cause deterioration.

[0005] The present disclosure aims to suppress deterioration of a work machine.

[0006] According to the present disclosure, there is provided a control system for a work machine including a controller, which acquires an operation signal for switching the direction of travel of the work machine, determines whether the operation signal satisfies the acquired operating condition while the work machine is traveling at a traveling speed equal to or greater than a first speed threshold, and prohibits output of a forward / reverse switch command for switching the direction of travel if it is determined that the operating condition is satisfied.

[0007] According to the present disclosure, there is provided a work machine control system including a controller, which acquires an operation signal for switching the traveling direction of the work machine, determines whether the operation signal satisfies the acquired operating condition when the work machine is descending a slope with an inclination angle equal to or greater than an angle threshold, and prohibits output of a forward / reverse switch command for switching the traveling direction if it is determined that the operating condition is satisfied.

[0008] According to the present disclosure, deterioration of the work machine is suppressed.

[0009] FIG. 1 is a diagram showing a remote operation system for a work machine according to the first embodiment. FIG. 2 is a configuration diagram showing a work machine and an operation device according to the first embodiment. FIG. 3 is a hardware configuration diagram showing an on-board controller according to the first embodiment. FIG. 4 is a diagram explaining the operation of a work machine according to the first embodiment. FIG. 5 is a functional block diagram showing a control system for a work machine according to the first embodiment. FIG. 6 is a flowchart showing a control method for a work machine according to the first embodiment. FIG. 7 is a timing chart showing a control method for a work machine according to the first embodiment. FIG. 8 is a diagram explaining the operation of a work machine according to a second embodiment. FIG. 9 is a diagram explaining the operation of a work machine according to the second embodiment. FIG. 10 is a functional block diagram showing a control system for a work machine according to the second embodiment. FIG. 11 is a flowchart showing a control method for a work machine according to the second embodiment. FIG. 12 is a timing chart showing a control method for a work machine according to the second embodiment.

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings, but the present disclosure is not limited to the embodiments. The components of the embodiments described below can be combined as appropriate. In addition, some components may not be used.

[0011] First Embodiment A first embodiment will be described.

[0012] <Remote Control System> Figure 1 is a diagram showing a remote control system 200 for a work machine 1 according to an embodiment. The remote control system 200 remotely controls a work machine 1 that is located at a work site 201. At least a part of the remote control system 200 is disposed in a remote control room 202 provided outside the work machine 1. The remote control system 200 comprises an operation device 7, a display device 8, and a remote controller 9.

[0013] The operation device 7 is disposed in the remote control room 202. The operation device 7 is operated by an operator in the remote control room 202. The operator can operate the operation device 7 while seated in the pilot seat 10. The operator may also operate a portable operation device 700. The operation device 700 may also be operated outside the remote control room 202.

[0014] The display device 8 is disposed in the remote control room 202. An example of the display device 8 is a flat panel display such as a liquid crystal display or an organic EL display. The display device 8 displays at least an image of the work site 201. The display device 8 may also output audio of the work site 201.

[0015] The operator operates the operation device 7 while checking an image of the work site 201 displayed on the display device 8. The work machine 1 is remotely controlled by the operation device 7.

[0016] The remote controller 9 is disposed in a remote operation room 202. The remote controller 9 and the work machine 1 communicate with each other via a communication system 203. Examples of the communication system 203 include the Internet, a local area network (LAN), a mobile phone communication network, and a satellite communication network.

[0017] <Work Machine> In this embodiment, the work machine 1 is a wheel loader. As shown in Figure 1 , the work machine 1 includes a vehicle body 2, an articulating mechanism 3, a cab 4, wheels 5, a work implement 6, and a camera 29. The work machine 1 travels on the wheels 5 at a work site 201. The work machine 1 performs work using the work implement 6 at the work site 201. Examples of work that the work machine 1 can perform include excavation work, loading work, transporting work, and snow removal work.

[0018] The vehicle body 2 supports the work implement 6. The vehicle body 2 includes a front frame 2F and a rear frame 2R. The front frame 2F is located forward of the rear frame 2R. The front frame 2F and the rear frame 2R are connected by an articulation mechanism 3. The articulation mechanism 3 includes an articulation cylinder 11. The articulation cylinder 11 is a hydraulic cylinder. The articulation cylinder 11 connects the front frame 2F and the rear frame 2R. When the articulation cylinder 11 extends and retracts, the front frame 2F bends left and right relative to the rear frame 2R. When the front frame 2F bends relative to the rear frame 2R, the traveling direction of the work machine 1 is adjusted. The cab 4 is located on top of the rear frame 2R.

[0019] The wheels 5 support the vehicle body 2. The wheels 5 include front wheels 5F attached to the front frame 2F and rear wheels 5R attached to the rear frame 2R. The front wheels 5F rotate about a rotation axis CXf. The rear wheels 5R rotate about a rotation axis CXr. When the work machine 1 travels in a straight line, the rotation axis CXf of the front wheels 5F and the rotation axis CXr of the rear wheels 5R are parallel. The rotation of the wheels 5 allows the work machine 1 to travel on the ground at the work site 201.

[0020] The work implement 6 is supported by the vehicle body 2. The work implement 6 is connected to the front frame 2F. The work implement 6 has a boom 12, a bucket 13, a bell crank 14, and a bucket link 15.

[0021] A base end of the boom 12 is rotatably connected to the front frame 2F. The boom 12 rotates about a rotation axis AXa relative to the front frame 2F. A bracket 16 is fixed to the middle portion of the boom 12.

[0022] The bucket 13 is a work member used to excavate an object to be excavated. The bucket 13 holds the material to be excavated. The bucket 13 has a cutting edge 13A, an opening 13B, and a bottom surface 13C. The material to be excavated enters the bucket 13 from the outside to the inside through the opening 13B, and exits the bucket 13 from the inside to the outside through the opening 13B. The cutting edge 13A is located at the bottom end of the opening 13B. The bottom surface 13C is located so as to extend rearward from the cutting edge 13A.

[0023] A base end of the bucket 13 is rotatably connected to the tip end of the boom 12. The bucket 13 rotates about a rotation axis AXb relative to the boom 12. The bucket 13 is disposed forward of the front wheels 5F. A bracket 17 is fixed to a part of the bucket 13.

[0024] An intermediate portion of the bell crank 14 is rotatably connected to a bracket 16 of the boom 12. The bell crank 14 rotates about a rotation axis AXc with respect to the bracket 16 of the boom 12. A lower end of the bell crank 14 is rotatably connected to a base end of a bucket link 15.

[0025] A tip end of the bucket link 15 is rotatably connected to a bracket 17 of the bucket 13. The bucket link 15 rotates about a rotation axis AXd relative to the bracket 17 of the bucket 13. The bell crank 14 is connected to the bucket 13 via the bucket link 15.

[0026] The boom 12 is operated by a boom cylinder 18. The boom cylinder 18 is a hydraulic cylinder. A base end of the boom cylinder 18 is connected to the front frame 2F. A tip end of the boom cylinder 18 is connected to the boom 12. The boom 12 rotates relative to the boom cylinder 18 about a rotation axis AXe.

[0027] The bucket 13 is operated by a bucket cylinder 19. The bucket cylinder 19 is a hydraulic cylinder. A base end of the bucket cylinder 19 is connected to the front frame 2F. A tip end of the bucket cylinder 19 is connected to an upper end of a bell crank 14. The bell crank 14 rotates relative to the bucket cylinder 19 about a rotation axis AXf.

[0028] The pivot axis AXa, the pivot axis AXb, the pivot axis AXc, the pivot axis AXd, the pivot axis AXe, the pivot axis AXf, and the rotation axis CXf of the front wheel 5F are parallel to each other. When the work machine 1 travels in a straight line, the pivot axis AXa of the work implement 6 and the rotation axis CXr of the rear wheel 5R are parallel to each other.

[0029] The camera 29 captures an image of the work site 201. The camera 29 captures an image of at least the work site 201 in front of the work machine 1. The camera 29 captures an image of at least a portion of the work implement 6. In this embodiment, the camera 29 is arranged in the cab 4.

[0030] <Configuration of Work Machine and Operating Device> Figure 2 is a configuration diagram showing a work machine 1 and an operating device 7 according to an embodiment. As shown in Figure 2, the work machine 1 is equipped with an engine 20, a power take-off (PTO) 21, a power transmission device 22, a brake device 23, a steering pump 24A, a steering control valve 37, an articulate cylinder 11, a work implement pump 24B, a boom control valve 38, a bucket control valve 39, a boom cylinder 18, a bucket cylinder 19, an inclination sensor 25, a vehicle speed sensor 26, a work implement attitude sensor 28, a load sensor 27, a camera 29, and an on-board controller 30.

[0031] The engine 20 is a drive source for the work machine 1. The engine 20 is supported by the vehicle body 2. A power take-off 21 distributes the drive force of the engine 20 to a power transmission device 22, a steering pump 24A, and a work implement pump 24B.

[0032] The power transmission device 22 transmits the driving force of the engine 20 to the wheels 5. The power transmission device 22 controls the traveling direction of the work machine 1. The traveling direction of the work machine 1 includes a forward direction and a reverse direction. The power transmission device 22 switches between forward and reverse traveling of the work machine 1. The power transmission device 22 may be a transmission having a plurality of speed change gears, or a transmission having a torque converter. The power transmission device 22 may be a hydraulic static transmission (HST) that combines a hydraulic pump and a hydraulic motor, or a hydraulic mechanical continuously variable transmission (HMT) that combines an HST and a planetary gear mechanism.

[0033] The brake device 23 reduces the traveling speed of the work machine 1. The brake device 23 brakes the work machine 1. The brake device 23 is a service brake. The brake device 23 has brake rotors provided on the front wheels 5F and the rear wheels 5R, respectively, and brake pads that are pressed against the brake rotors. The brake device 23 is capable of adjusting the braking force. The stronger the force pressing the brake pads against the brake rotors, the stronger the braking force.

[0034] The steering pump 24A is a hydraulic pump that is operated by the driving force generated by the engine 20. The hydraulic oil discharged from the steering pump 24A is supplied to the articulated cylinder 11 via a steering control valve 37. The steering control valve 37 controls the flow rate and direction of the hydraulic oil supplied from the steering pump 24A to the articulated cylinder 11.

[0035] The work implement pump 24B is a hydraulic pump that is operated by the driving force generated by the engine 20. The hydraulic oil discharged from the work implement pump 24B is supplied to the boom cylinder 18 via a boom control valve 38. The hydraulic oil discharged from the work implement pump 24B is supplied to the bucket cylinder 19 via a bucket control valve 39. The boom control valve 38 controls the flow rate and direction of the hydraulic oil supplied from the work implement pump 24B to the boom cylinder 18. The bucket control valve 39 controls the flow rate and direction of the hydraulic oil supplied from the work implement pump 24B to the bucket cylinder 19. The work implement 6 is operated by the hydraulic oil from the work implement pump 24B.

[0036] The inclination sensor 25 detects the inclination angle of the vehicle body 2 of the work machine 1. The inclination sensor 25 detects the inclination angle of the vehicle body 2 with respect to a horizontal plane. The inclination sensor 25 may detect the inclination angle of the front frame 2F or the inclination angle of the rear frame 2R. An example of the inclination sensor 25 is an inertial sensor (IMU: Inertial Measurement Unit) disposed on the vehicle body 2. The detection data of the inclination sensor 25 represents inclination data that indicates the inclination angle of the vehicle body 2 of the work machine 1.

[0037] The vehicle speed sensor 26 detects the traveling speed of the work machine 1. An example of the vehicle speed sensor 26 is a magnetic sensor that detects the rotation speed of a drive shaft connected to the wheels 5.

[0038] The work implement attitude sensor 28 detects the attitude of the work implement 6. The attitude of the work implement 6 includes the angle of the work implement 6. The work implement attitude sensor 28 includes a boom angle sensor 28A that detects the attitude of the boom 12 and a bucket angle sensor 28B that detects the attitude of the bucket 13.

[0039] The attitude of the boom 12 includes the angle of the boom 12. The boom angle sensor 28A detects a boom angle that indicates the angle of the boom 12. The boom angle refers to the angle of the boom 12 with respect to the vehicle body 2 in the local coordinate system. In the embodiment, the boom angle is the angle between a line connecting the rotation axis AXa and the rotation axis AXb and a line connecting the rotation axis CXf and the rotation axis CXr when the work machine 1 is traveling in a straight line. An example of the boom angle sensor 28A is an angle sensor that is arranged at the connection between the front frame 2F and the boom 12.

[0040] The attitude of the bucket 13 includes the angle of the bucket 13. The bucket angle sensor 28B detects a bucket angle that indicates the angle of the bucket 13. The bucket angle refers to the angle of the bucket 13 with respect to the boom 12 in a local coordinate system. In this embodiment, the bucket angle is the angle between a line connecting the rotation axis AXb and the cutting edge 13A and a line connecting the rotation axis AXa and the rotation axis AXb. An example of the bucket angle sensor 28B is an angle sensor that is disposed at the connection between the boom 12 and the bell crank 14. In this embodiment, the bucket angle sensor 28B detects a bell crank angle that indicates the angle of the bell crank 14 with respect to the boom 12 in the local coordinate system. The bell crank angle is the angle between a line connecting the rotation axis AXc and the rotation axis AXf and a line connecting the rotation axis AXa and the rotation axis AXb. The bucket angle and the bell crank angle have a one-to-one correspondence. The bucket angle sensor 28B detects the bell crank angle. The bucket angle is calculated based on the detected data of the bell crank angle and the detected data of the boom angle.

[0041] The boom angle and bucket angle are each angles in the operating plane of the work implement 6 that is perpendicular to the rotation axis AXa. The line connecting the rotation axis AXa and the rotation axis AXb, the line connecting the rotation axis AXc and the rotation axis AXf, the line connecting the rotation axis AXb and the cutting edge 13A, and the line connecting the rotation axis CXf and the rotation axis CXr when the work machine 1 is traveling in a straight line are each lines in the operating plane of the work implement 6.

[0042] The load sensor 27 detects the load state of the work implement 6. The load sensor 27 detects whether the bucket 13 is in a loaded state, in which it holds excavated material, or in an empty state, in which it does not hold any excavated material. In this embodiment, the load sensor 27 includes a weight sensor that detects the weight of the work implement 6. The weight of the work implement 6 differs between a loaded state, in which the bucket 13 holds excavated material, and an empty state, in which it does not hold any excavated material. The load sensor 27 can detect whether the work implement 6 is in a loaded state or an empty state by detecting the weight of the work implement 6. An example of the load sensor 27 is a bottom pressure sensor that detects the bottom pressure of the boom cylinder 18.

[0043] The camera 29 captures an image of the work site 201. The camera 29 captures an image of at least a portion of the work machine 6. The image data captured by the camera 29 is transmitted to the remote controller 9 via the on-board controller 30 and the communication system 203. The remote controller 9 displays the image data captured by the camera 29 on the display device 8.

[0044] The operation device 7 is operated by an operator. When operated by the operator, the operation device 7 generates an operation signal for operating the work machine 1. The operation signal generated by the operation device 7 is transmitted to the on-board controller 30 via the remote controller 9 and the communication system 203. The on-board controller 30 outputs a control command for operating the work machine 1 based on the operation signal transmitted from the remote controller 9. The operation device 7 includes a traveling system operation device 7A and a work implement operation device 7B.

[0045] The traveling system operation device 7A is operated by an operator to operate at least one of the engine 20, the power transmission device 22, and the brake device 23. The traveling system operation device 7A generates an operation signal to operate at least one of the engine 20, the power transmission device 22, and the brake device 23. The traveling system operation device 7A includes an accelerator pedal 71, a brake pedal 72, a steering wheel 73, a forward / reverse switch lever 74, and a speed setting device 77.

[0046] The accelerator pedal 71 is operated to increase the traveling speed of the work machine 1. The brake pedal 72 is operated to decrease the traveling speed of the work machine 1. The steering wheel 73 is operated to adjust the traveling direction of the work machine 1. The forward / reverse selector lever 74 is operated to switch the traveling direction of the work machine 1. The forward / reverse selector lever 74 is operated to switch the work machine 1 between moving forward and reversing.

[0047] The speed stage setting device 77 is operated to set the speed stage of the transmission or the maximum value of the traveling speed of the work machine 1. The speed stage setting device 77 includes a lever or a dial. In the case of a transmission having a torque converter, the upper limit of the speed stage is set by operating the speed stage setting device 77. When the upper limit of the speed stage is set to first gear, the work machine 1 can travel at a traveling speed of 0 km / h or more and 6 km / h or less. When the upper limit of the speed stage is set to second gear, the work machine 1 can travel at a traveling speed of 0 km / h or more and 15 km / h or less. When the upper limit of the speed stage is set to third gear, the work machine 1 can travel at a traveling speed of 0 km / h or more and 23 km / h or less. When the upper limit of the speed stage is set to fourth gear, the work machine 1 can travel at a traveling speed of 0 km / h or more and 38 km / h or less. For example, when the work machine 1 excavates an excavation target, the upper limit of the speed stage is set to first gear, when the work machine 1 performs a so-called V-shape operation, the upper limit of the speed stage is set to second gear, when the work machine 1 travels in a loaded state, the upper limit of the speed stage is set to third gear, and when the work machine 1 travels in an unloaded state, the upper limit of the speed stage is set to fourth gear. When the power transmission device 22 is a hydrostatic continuously variable transmission (HST) or a hydromechanical continuously variable transmission (HMT), the maximum traveling speed of the work machine 1 is set by operating the speed stage setting device 77.

[0048] The work implement operating device 7B is operated by an operator to operate the work implement 6. The work implement operating device 7B generates an operation signal to operate the work implement 6. The work implement operating device 7B includes a boom lever 75 and a bucket lever 76.

[0049] The boom lever 75 is operated to raise or lower the boom 12. The bucket lever 76 is operated to tilt or dump the bucket 13. The raising operation of the boom 12 refers to the operation of the boom 12 rotating about the rotation axis AXa so that the tip of the boom 12 moves away from the ground. The lowering operation of the boom 12 refers to the operation of the boom 12 rotating about the rotation axis AXa so that the tip of the boom 12 moves closer to the ground. The tilting operation of the bucket 13 refers to the operation of the bucket 13 rotating about the rotation axis AXb so that the opening 13B of the bucket 13 faces upward and the blade tip 13A moves away from the ground. The dumping operation of the bucket 13 refers to the operation of the bucket 13 rotating about the rotation axis AXb so that the opening 13B of the bucket 13 faces downward and the blade tip 13A moves closer to the ground.

[0050] <In-Vehicle Controller> FIG. 3 is a hardware configuration diagram showing an in-vehicle controller 30 according to an embodiment. The in-vehicle controller 30 includes a computer system. The in-vehicle controller 30 includes a processor 31 such as a central processing unit (CPU), a main memory 32 including a non-volatile memory such as a read-only memory (ROM) and a volatile memory such as a random access memory (RAM), a storage 33, an input / output interface 34 including an input / output circuit, and a communication interface 35 including a communication circuit. The functions of the in-vehicle controller 30 are stored in the storage 33 as a computer program. The processor 31 reads the computer program from the storage 33, loads it into the main memory 32, and executes processing in accordance with the computer program. The computer program may be distributed to the in-vehicle controller 30 via a network.

[0051] The remote controller 9 also includes a computer system. Like the in-vehicle controller 30, the remote controller 9 has a processor, a main memory, a storage, an input / output interface, and a communication interface.

[0052] <Operation of the Work Machine> Figure 4 is a diagram illustrating the operation of the work machine 1 according to the embodiment. At the work site 201, shuttle operation may be performed in which the forward / reverse switch lever 74 is operated while the work machine 1 is traveling. Shuttle operation includes operating the forward / reverse switch lever 74 to switch the traveling direction of the work machine 1 from forward to reverse while the work machine 1 is moving forward, and operating the forward / reverse switch lever 74 to switch the traveling direction of the work machine 1 from reverse to forward while the work machine 1 is moving backward. In shuttle operation, the forward / reverse switch lever 74 is operated to switch the traveling direction of the work machine 1 before the work machine 1 comes to a stop. By operating the forward / reverse switch lever 74 before the work machine 1 comes to a stop, the operator can quickly switch the traveling direction of the work machine 1.

[0053] When performing a shuttle operation, the operator often operates the boom lever 75 and the bucket lever 76 so that the work implement 6 assumes a predetermined posture. The predetermined posture of the work implement 6 is a posture that allows the work machine 1 to travel stably at a high traveling speed.

[0054] The work implement 6 includes a boom 12 rotatably connected to the front frame 2F of the work machine 1 about a rotation axis AXa (first rotation axis), and a bucket 13 rotatably connected to the boom 12 about a rotation axis AXb (second rotation axis). If a line connecting the rotation axis CXf of the front wheels 5F and the rotation axis CXr of the rear wheels 5R when the work machine 1 is traveling in a straight line is defined as a specified line RL, then the rotation axis AXa is positioned above the specified line RL. Up is the direction away from the ground on which the work machine 1 is traveling. The specified posture of the work implement 6 is a posture in which the rotation axis AXb is positioned closer to the specified line RL than the rotation axis AXa, the bottom surface 13C of the bucket 13 is tilted forward and away from the specified line RL, and the bucket 13 is off the ground. When the ground on which the work machine 1 is traveling is substantially parallel to the horizontal plane, i.e., when the specified line RL is parallel to the horizontal plane, the specified posture of the work implement 6 is a posture in which the rotation axis AXb is positioned below the rotation axis AXa, the bottom surface 13C of the bucket 13 is inclined upward toward the front, and the bucket 13 is off the ground.

[0055] In the following description, switching the direction of travel of the work machine 1 while the work machine 1 is traveling at a speed equal to or greater than a predetermined first speed threshold Sh1 will be referred to as high-speed shuttle operation as appropriate.

[0056] 5 is a functional block diagram showing a control system 100 of the work machine 1 according to the embodiment. The control system 100 has an operation device 7, a remote controller 9, an on-board controller 30, a vehicle speed sensor 26, a work machine attitude sensor 28, a load sensor 27, and a camera 29.

[0057] The on-board controller 30 has a sensor data acquisition unit 101 , an operation signal acquisition unit 102 , a condition determination unit 103 , a travel control unit 104 , a work machine control unit 105 , a threshold setting unit 106 , and a transmission unit 107 .

[0058] The sensor data acquisition unit 101 acquires detection data from the vehicle speed sensor 26, detection data from the work implement attitude sensor 28, and detection data from the load sensor 27. The detection data from the work implement attitude sensor 28 includes detection data from a boom angle sensor 28A indicating the boom angle, and detection data from a bucket angle sensor 28B indicating the bucket angle.

[0059] The operation signal acquisition unit 102 acquires operation signals from the operation device 7. The operation signals from the operation device 7 include an operation signal from an accelerator pedal 71 operated to increase the traveling speed of the work machine 1, an operation signal from a brake pedal 72 operated to decrease the traveling speed of the work machine 1, an operation signal from a steering wheel 73 operated to adjust the traveling direction of the work machine 1, an operation signal from a forward / reverse switch lever 74 operated to switch the traveling direction of the work machine 1, and an operation signal from a speed stage setting device 77 operated to set a transmission speed stage or a maximum traveling speed of the work machine 1. The operation signals from the operation device 7 also include an operation signal from a boom lever 75 operated to operate the boom 12, and an operation signal from a bucket lever 76 operated to operate the bucket 13.

[0060] The condition determination unit 103 determines whether the work machine 1 satisfies high-speed shuttle operation conditions. The high-speed shuttle operation conditions include the forward / reverse switch lever 74 being operated to switch the traveling direction of the work machine 1 while the work machine 1 is traveling at a traveling speed equal to or greater than a predetermined first speed threshold Sh1. The condition determination unit 103 determines whether an operation signal from the forward / reverse switch lever 74 for switching the traveling direction of the work machine 1 while the work machine 1 is traveling at a traveling speed equal to or greater than the first speed threshold Sh1 satisfies the acquired high-speed shuttle operation conditions. The first speed threshold Sh1 is, for example, 15 km / h. The first speed threshold Sh1 is set to the same value as the traveling speed when the work machine 1 moves between work sites. The first speed threshold Sh1 may also be set to the maximum traveling speed when the upper limit of the speed range in a transmission having a torque converter is set to third or fourth gear.

[0061] The traveling speed of the work machine 1 is detected by the vehicle speed sensor 26. The detection data of the vehicle speed sensor 26 is acquired by the sensor data acquisition unit 101. An operation signal from the forward / reverse switch lever 74, which is operated to switch the traveling direction of the work machine 1, is acquired by the operation signal acquisition unit 102. The condition determination unit 103 can determine whether the work machine 1 is traveling at a traveling speed equal to or greater than the first speed threshold Sh1, based on the detection data of the vehicle speed sensor 26 acquired by the sensor data acquisition unit 101. The condition determination unit 103 can determine whether the traveling direction of the work machine 1 has been switched, based on the operation signal from the forward / reverse switch lever 74 acquired by the operation signal acquisition unit 102.

[0062] In the embodiment, the high-speed shuttle operation condition includes the posture of the work implement 6 being a predetermined posture. As described above, the predetermined posture of the work implement 6 is a posture in which the rotation axis AXb is positioned lower than the rotation axis AXa, the bottom surface 13C of the bucket 13 is tilted upward and forward, and the bucket 13 is off the ground. The predetermined posture of the work implement 6 includes a posture in which the bucket 13 is off the ground, for example, by 10 cm or more.

[0063] The posture of the work implement 6 is detected by a work implement posture sensor 28. Detection data of the work implement posture sensor 28 is acquired by a sensor data acquisition unit 101. A condition determination unit 103 can determine whether or not the work implement 6 is in a predetermined posture based on the detection data of the work implement posture sensor 28 acquired by the sensor data acquisition unit 101.

[0064] The travel control unit 104 controls the travel of the work machine 1 based on operation signals from the travel system operation device 7A. Based on operation signals from the travel system operation device 7A, the travel control unit 104 adjusts the travel speed of the work machine 1, adjusts the travel direction of the work machine 1, and switches the work machine 1 between forward and reverse travel.

[0065] Furthermore, the traveling control unit 104 outputs control commands so that the power transmission device 22 and the brake device 23 each operate under predetermined conditions, regardless of the operation signal from the traveling system operation device 7A. Even if the forward / reverse switch lever 74 is operated, the traveling control unit 104 can output control commands so that the power transmission device 22 operates under predetermined conditions, regardless of the operation signal from the forward / reverse switch lever 74. Even if the brake pedal 72 is not operated, the traveling control unit 104 can output control commands so that the brake device 23 operates under predetermined conditions.

[0066] In the following description, the control command output from the travel control unit 104 to the power transmission device 22 to switch the direction of travel of the work machine 1 based on an operation signal from the forward / reverse switch lever 74 will be referred to as a manual forward / reverse switch command, as appropriate, and the control command output from the travel control unit 104 to the power transmission device 22 to switch the direction of travel of the work machine 1 regardless of the operation signal from the forward / reverse switch lever 74 will be referred to as an automatic forward / reverse switch command, as appropriate.

[0067] In the following description, a control command output from the travel control unit 104 to the brake device 23 to brake the work machine 1 based on an operation signal from the brake pedal 72 will be referred to as a manual brake command, as appropriate, and a control command output from the travel control unit 104 to the brake device 23 to brake the work machine 1 regardless of an operation signal from the brake pedal 72 will be referred to as an automatic brake command, as appropriate. Furthermore, the state in which the brake device 23 operates based on an automatic brake command will be referred to as automatic braking, as appropriate.

[0068] In this embodiment, when the condition determination unit 103 determines that the high-speed shuttle operation conditions are satisfied, the travel control unit 104 prohibits the output of an automatic forward / reverse switch command that switches the traveling direction of the work machine 1. When the condition determination unit 103 determines that the high-speed shuttle operation conditions are satisfied, the travel control unit 104 outputs an automatic brake command to the brake device 23 that reduces the traveling speed of the work machine 1, and then outputs an automatic forward / reverse switch command to the power transmission device 22 that switches the traveling direction of the work machine 1.

[0069] The travel control unit 104 outputs an automatic forward / reverse switch command after the travel speed of the work machine 1 drops to a predetermined second speed threshold Sh2 or below due to an automatic brake command. The second speed threshold Sh2 is a value smaller than the first speed threshold Sh1. The second speed threshold Sh2 is, for example, 10 km / h. The second speed threshold Sh2 is set to the same value as the travel speed when the work machine 1 is performing excavation work or loading work. The second speed threshold Sh2 may be set to the maximum travel speed when the upper limit of the speed stage in a transmission having a torque converter is set to second gear.

[0070] When an automatic brake command is output while the work machine 1 is traveling at a traveling speed equal to or greater than the first speed threshold Sh1, the traveling speed of the work machine 1 decreases below the first speed threshold Sh1 and eventually decreases to equal to or less than the second speed threshold Sh2. After the traveling speed of the work machine 1 decreases to equal to or less than the second speed threshold Sh2, the travel control unit 104 stops outputting the automatic brake command. Stopping the output of the automatic brake command deactivates the brake device 23. After the activation of the brake device 23 is deactivated, the travel control unit 104 outputs an automatic forward / reverse switch command to the power transmission device 22 to switch the traveling direction of the work machine 1. The traveling direction of the work machine 1 is switched by outputting the automatic forward / reverse switch command. Note that after the traveling speed of the work machine 1 decreases to equal to or less than the second speed threshold Sh2, the travel control unit 104 may start outputting the automatic forward / reverse switch command before the activation of the brake device 23 is deactivated.

[0071] The travel control unit 104 may adjust the command value of the automatic brake command based on the travel speed of the work machine 1 when the work machine 1 is traveling at a travel speed equal to or greater than the first speed threshold Sh1. The larger the command value of the automatic brake command, the stronger the braking force by the brake device 23, and the smaller the command value of the automatic brake command, the weaker the braking force by the brake device 23. In an embodiment, the larger the command value of the automatic brake command, the stronger the force pressing the brake pads against the brake rotor, and the smaller the command value of the automatic brake command, the weaker the force pressing the brake pads against the brake rotor. The travel control unit 104 may output an automatic brake command such that the braking force becomes stronger the higher the travel speed of the work machine 1. By adjusting the command value of the automatic brake command so that the braking force becomes stronger the higher the travel speed of the work machine 1, the travel speed of the work machine 1 becomes equal to or less than the second speed threshold Sh2 in a short period of time.

[0072] Note that when the work machine 1 is traveling at a traveling speed equal to or greater than the first speed threshold Sh1, there is a possibility that the operator will operate the forward / reverse switch lever 74 while operating the brake pedal 72. Even if the brake pedal 72 is operated, there is a possibility that the forward / reverse switch lever 74 will be operated before the traveling speed of the work machine 1 becomes less than the first speed threshold Sh1. Even if the brake pedal 72 is operated, the travel control unit 104 may output an automatic brake command regardless of an operation signal from the brake pedal 72. The travel control unit 104 may adjust the command value of the automatic brake command based on an operation signal from the brake pedal 72. The travel control unit 104 calculates a target brake command value so as to obtain a target braking force, and calculates a command value of a manual brake command based on an operation signal from the brake pedal 72. The travel control unit 104 calculates the difference between the target brake command value and the command value of the manual brake command as the command value of the automatic brake command. The traveling control unit 104 may output a brake command having a command value obtained by adding the command value of the manual brake command and the command value of the automatic brake command so as to obtain a target braking force.

[0073] It should be noted that while an automatic brake command is being output, there is a possibility that the operator will operate the accelerator pedal 71. Even if the accelerator pedal 71 is operated, the cruise control unit 104 outputs the automatic brake command regardless of the operation signal from the accelerator pedal 71. Furthermore, if the accelerator pedal 71 is operated while an automatic brake command is being output, the cruise control unit 104 may output the automatic brake command regardless of the operation signal from the accelerator pedal 71, and may also output a control command to reduce the output (rotation speed) of the engine 20.

[0074] The work machine control unit 105 controls the work machine 6 based on an operation signal from the work machine operating device 7B. The work machine control unit 105 controls the boom control valve 38 based on an operation signal from the boom lever 75. By controlling the boom control valve 38, the boom cylinder 18 extends and retracts, and the boom 12 performs a raising and lowering operation. The work machine control unit 105 controls the bucket control valve 39 based on an operation signal from the bucket lever 76. By controlling the bucket control valve 39, the bucket cylinder 19 extends and retracts, and the bucket 13 performs a tilting operation and a dumping operation.

[0075] The threshold setting unit 106 changes the first speed threshold Sh1 based on the detection data of the load sensor 27. The threshold setting unit 106 can determine whether the work machine 6 is in a loaded state or an unloaded state based on the detection data of the load sensor 27. The threshold setting unit 106 sets the first speed threshold Sh1 when the work machine 6 is in a loaded state to be smaller than the first speed threshold Sh1 when the work machine 6 is in an unloaded state. When the work machine 6 is in a loaded state, it is determined that the high-speed shuttle operation condition is satisfied even if the traveling speed of the work machine 1 is low. For example, if the first speed threshold Sh1 when the work machine 6 is in an unloaded state is 15 km / h, the first speed threshold Sh1 when the work machine 6 is in a loaded state is set to 13 km / h.

[0076] The threshold setting unit 106 changes the second speed threshold Sh2 based on the detection data of the load sensor 27. The threshold setting unit 106 can determine whether the work implement 6 is in a loaded state or an unloaded state based on the detection data of the load sensor 27. The threshold setting unit 106 sets the second speed threshold Sh2 when the work implement 6 is in a loaded state to be smaller than the second speed threshold Sh2 when the work implement 6 is in an unloaded state. When the work implement 6 is in a loaded state, an automatic forward / reverse switching command is output after the traveling speed of the work machine 1 has sufficiently decreased. For example, if the second speed threshold Sh2 when the work implement 6 is in an unloaded state is 10 km / h, the second speed threshold Sh2 when the work implement 6 is in a loaded state is set to 8 km / h.

[0077] The transmission unit 107 transmits image data captured by the camera 29 to the remote controller 9. The transmission unit 107 may also transmit detection data of the work machine attitude sensor 28 to the remote controller 9.

[0078] <Construction machine control method> Figure 6 is a flowchart showing a control method for the construction machine 1 according to the embodiment. The operation signal acquisition unit 102 acquires an operation signal from the operation device 7. The travel control unit 104 controls the travel of the construction machine 1 based on an operation signal from the traveling system operation device 7A. The work implement control unit 105 controls the construction machine 6 based on an operation signal from the work implement operation device 7B. The sensor data acquisition unit 101 acquires detection data from the vehicle speed sensor 26, detection data from the work implement attitude sensor 28, and detection data from the load sensor 27 (step S1).

[0079] The threshold setting unit 106 sets the first speed threshold Sh1 and the second speed threshold Sh2 based on the detection data of the cargo sensor 27 .

[0080] The condition determination unit 103 determines whether or not the high-speed shuttle operation conditions are satisfied based on the detection data from the vehicle speed sensor 26, which detects the traveling speed of the work machine 1, and the operation signal from the forward / reverse switch lever 74. In other words, the condition determination unit 103 determines whether or not the operation signal acquisition unit 102 has acquired an operation signal from the forward / reverse switch lever 74 to switch the traveling direction of the work machine 1 while the work machine 1 is traveling at a traveling speed equal to or greater than the first speed threshold Sh1 (step S2).

[0081] If it is determined in step S2 that the high-speed shuttle operation conditions are satisfied (step S2: Yes), the travel control unit 104 outputs an automatic brake command to the brake device 23 to reduce the travel speed of the work machine 1, while prohibiting the output of an automatic forward / reverse switching command that switches the direction of travel of the work machine 1 (step S3).

[0082] After outputting the automatic brake command, the travel control unit 104 determines whether the travel speed of the work machine 1 has decreased to or below the second speed threshold Sh2 based on the detection data of the vehicle speed sensor 26 (step S4).

[0083] In step S4, if it is determined that the traveling speed of the work machine 1 has not decreased to or below the second speed threshold Sh2 (step S4: No), the traveling control unit 104 continues to output the automatic brake command.

[0084] If it is determined in step S4 that the traveling speed of the work machine 1 has dropped to or below the second speed threshold Sh2 (step S4: Yes), the travel control unit 104 stops outputting the automatic brake command. Stopping the output of the automatic brake command deactivates the brake device 23. After the traveling speed of the work machine 1 has dropped to or below the second speed threshold Sh2, the travel control unit 104 outputs an automatic forward / reverse switch command to the power transmission device 22 to switch the traveling direction of the work machine 1 (step S5). The traveling direction of the work machine 1 is switched by outputting the automatic forward / reverse switch command.

[0085] If it is determined in step S2 that the high-speed shuttle operation conditions are not satisfied, that is, if an operation signal has been acquired from the forward / reverse switch lever 74 to switch the traveling direction of the work machine 1 but the traveling speed of the work machine 1 is less than the first speed threshold Sh1 (step S2: No), the travel control unit 104 outputs a manual forward / reverse switch command to the power transmission device 22 without outputting an automatic brake command (step S6). By outputting the manual forward / reverse switch command, the traveling direction of the work machine 1 is switched.

[0086] Figure 7 is a timing chart showing a control method for the work machine 1 according to the embodiment. In the following description, it is assumed that the power transmission device 22 has a forward clutch, a reverse clutch, and a torque converter. The work machine 1 moves forward when the forward clutch is engaged. The work machine 1 moves backward when the reverse clutch is engaged. Furthermore, in the following description, a control command for moving the work machine 1 forward will be referred to as a forward command, and a control command for moving the work machine 1 backward will be referred to as a reverse command, as appropriate. A forward command is a control command for engaging the forward clutch. A reverse command is a control command for engaging the reverse clutch.

[0087] 7, the horizontal axis represents time, and the vertical axis represents the travel speed of the work machine 1, the operation signal from the forward / reverse selector lever 74, the command value of the forward command output from the travel control unit 104 to the forward clutch and the clutch pressure of the forward clutch, the command value of the reverse command output from the travel control unit 104 to the reverse clutch and the clutch pressure of the reverse clutch, and the command value and braking force of the automatic brake command output from the travel control unit 104 to the brake device 23.

[0088] 7 shows a state in which the work machine 1 has been moving forward at a traveling speed Ts since time t0. When the operation signal from the forward / reverse selector lever 74 is an operation signal Sf that moves the work machine 1 forward, the travel control unit 104 outputs a forward command of command value Vf to the forward clutch based on the operation signal Sf. When the forward command is output, the forward clutch is engaged at a predetermined clutch pressure Pf. Engaging the forward clutch causes the work machine 1 to move forward.

[0089] At time t1, the forward / reverse selector lever 74 is operated. At time t1, the operation signal from the forward / reverse selector lever 74 switches from an operation signal Sf that moves the work machine 1 forward to an operation signal Sr that moves the work machine 1 backward. At time t1, the traveling speed Ts of the work machine 1 is equal to or greater than the first speed threshold Sh1. Therefore, the condition determination unit 103 determines that the high-speed shuttle operation condition is satisfied at time t1.

[0090] Because it is determined that the high-speed shuttle operation condition is satisfied at time t1, the travel control unit 104 outputs an automatic brake command of command value Vb to reduce the travel speed Ts of the work machine 1. The travel control unit 104 continues to output the automatic brake command until the travel speed Ts of the work machine 1 becomes equal to or less than the second speed threshold Sh2. In the example shown in Figure 7, at time t2, the travel speed Ts of the work machine 1 reduces to the second speed threshold Sh2.

[0091] In this embodiment, the traveling control unit 104 gradually increases the command value Vb of the automatic brake command from time t1. Because the command value Vb gradually increases, the braking force Fb by the brake device 23 gradually increases. Because the command value Vb gradually increases, the automatic brake is prevented from suddenly operating.

[0092] The travel control unit 104 does not output an automatic forward / reverse switch command until the travel speed Ts of the work machine 1 becomes equal to or less than the second speed threshold Sh2. The forward command continues to be output during the period between time t1 and time t2, and the forward clutch is maintained engaged.

[0093] If, at time t2, it is determined that the traveling speed Ts of the work machine 1 has become equal to or less than the second speed threshold Sh2, the traveling control unit 104 stops outputting the forward command and outputs a reverse command of command value Vr to the reverse clutch. When the reverse command is output, the torque converter generates a braking force and the reverse clutch is engaged at a predetermined clutch pressure Pr. When the reverse clutch is engaged, the work machine 1 moves in reverse. When the forward clutch is disengaged, the clutch pressure Pf of the forward clutch gradually decreases. When the reverse clutch is engaged, the clutch pressure Pr of the reverse clutch gradually increases.

[0094] At time t2, the traveling control unit 104 gradually decreases the command value Vb of the automatic brake command. The command value Vb of the automatic brake command gradually decreases from time t2. Because the command value Vb gradually decreases, the braking force Fb by the brake device 23 gradually weakens. Because the command value Vb gradually decreases, the automatic brake is prevented from being suddenly released.

[0095] At time t2, the travel control unit 104 stops outputting the forward command and outputs a reverse command of command value Vr to the reverse clutch. When the reverse command is output, the reverse clutch is engaged at a predetermined clutch pressure Pr. When the reverse clutch is engaged, the work machine 1 moves in reverse. When the forward clutch is disengaged, the clutch pressure Pf of the forward clutch gradually decreases. When the reverse clutch is engaged, the clutch pressure Pr of the reverse clutch gradually increases.

[0096] <Effects> As described above, in the embodiment, the control system 100 of the work machine 1 includes an on-board controller 30. The on-board controller 30 has an operation signal acquisition unit 102 that acquires an operation signal from the forward / reverse switch lever 74, which is an operating device that is operated to switch the traveling direction of the work machine 1, a condition determination unit 103 that determines whether the operation signal from the forward / reverse switch lever 74 for switching the traveling direction of the work machine 1 while the work machine 1 is traveling at a traveling speed equal to or greater than the first speed threshold Sh1 satisfies the acquired high-speed shuttle operation condition, and a travel control unit 104 that prohibits the output of an automatic forward / reverse switch command to switch the traveling direction of the work machine 1 when it is determined that the high-speed shuttle operation condition is satisfied.

[0097] According to this embodiment, even if the forward / reverse selector lever 74 is operated during shuttle operation while the work machine 1 is traveling at a high traveling speed, the direction of travel of the work machine 1 is prohibited from being changed. This prevents deterioration of the power transmission device 22.

[0098] In the embodiment, the travel control unit 104 outputs an automatic brake command to reduce the travel speed of the work machine 1, and then outputs an automatic forward / reverse switch command to switch the direction of travel of the work machine 1. According to the embodiment, during shuttle operation, if the forward / reverse switch lever 74 is operated while the work machine 1 is traveling at a high travel speed, the automatic brake is activated before the power transmission device 22 is activated. After the travel speed of the work machine 1 is reduced by activation of the automatic brake, the power transmission device 22 is activated so as to switch the direction of travel of the work machine 1. Because the power transmission device 22 is activated after the travel speed of the work machine 1 is reduced by the automatic brake, the load on the power transmission device 22 is reduced. As a result, deterioration of the power transmission device 22 is suppressed.

[0099] When the work machine 1 is traveling at a high traveling speed, the rotating members of the power transmission device 22, such as the clutch, also rotate at a high rotational speed. When the work machine 1 is traveling forward at a high traveling speed, the rotating members of the power transmission device 22 rotate at a high rotational speed in the forward direction, and when the work machine 1 is traveling backward at a high traveling speed, the rotating members of the power transmission device 22 rotate at a high rotational speed in the reverse direction. For example, when the work machine 1 is traveling forward at a high traveling speed and the power transmission device 22 operates to switch the traveling direction of the work machine 1 based on an operation signal from the forward / reverse selector lever 74, the rotating members that are rotating in the forward direction at a high rotational speed will suddenly rotate in the reverse direction. This could result in a high load being applied to the rotating members.

[0100] According to this embodiment, after the travel speed of the work machine 1 is reduced by activation of the automatic brake, the power transmission device 22 operates to switch the traveling direction of the work machine 1. In other words, after the rotational speed of the rotating member rotating in the forward direction is reduced, the rotating member is rotated in the reverse direction. This prevents a high load from being applied to the rotating member. This therefore prevents deterioration of the power transmission device 22.

[0101] When the work machine 1 is remotely operated, it is difficult for the operator in the remote control cabin 202 to realize that the work machine 1 is traveling at a high traveling speed. For this reason, there is a possibility that the operator may unconsciously operate the forward / reverse switch lever 74 while the work machine 1 is traveling at a speed that would be too dangerous for the operator to operate while on board and operating it. If such an operation is performed, the load on the power transmission device 22 increases, and excessive load is also placed on the vehicle body 2, accelerating deterioration of the work machine 1. According to the embodiment, if the forward / reverse switch lever 74 is operated while the work machine 1 is traveling at a high traveling speed, the automatic brake is activated and then the direction of travel of the work machine 1 is changed. Therefore, deterioration of the work machine 1 is suppressed.

[0102] The travel control unit 104 outputs an automatic forward / reverse switch command after the travel speed of the work machine 1 has fallen to or below the second speed threshold Sh2 due to an automatic brake command. After the automatic brake is activated and the travel speed of the work machine 1 has fallen sufficiently, the direction of travel of the work machine 1 is switched. This prevents deterioration of the work machine 1.

[0103] The travel control unit 104 stops outputting the automatic brake command after the travel speed of the work machine 1 drops below the second speed threshold Sh2. For example, after the travel speed of the work machine 1 moving forward drops below the second speed threshold Sh2, the output of the automatic brake command is stopped, allowing the work machine 1 to smoothly start reversing.

[0104] The high-speed shuttle operation conditions include a predetermined posture in which the rotation axis AXb is positioned below the rotation axis AXa, the bottom surface 13C of the bucket 13 is tilted upward and forward, and the bucket 13 is off the ground. Because the work implement 6 is in the predetermined posture, the work machine 1 can travel stably at a high traveling speed. If the high-speed shuttle operation conditions do not include the work implement 6 being in the predetermined posture, the work efficiency of the work machine 1 may decrease. For example, if the automatic brake is activated when the travel direction of the work machine 1 changes while the boom 12 is in the raised posture, the weight balance of the work machine 1 may be disrupted. If the automatic brake is activated when the travel direction of the work machine 1 changes while the bucket 13 is in an excavation posture in which it is in contact with the ground, this will affect the excavation operation. Because the high-speed shuttle operation conditions include the work implement 6 being in the predetermined posture, a decrease in the work efficiency of the work machine 1 is suppressed.

[0105] The threshold setting unit 106 changes the first speed threshold Sh1 and the second speed threshold Sh2 based on detection data from the load sensor 27 that detects the weight of the work implement 6. The threshold setting unit 106 sets the first speed threshold Sh1 when the work implement 6 is in a loaded state to be smaller than the first speed threshold Sh1 when the work implement 6 is in an unloaded state. The threshold setting unit 106 sets the second speed threshold Sh2 when the work implement 6 is in a loaded state to be smaller than the second speed threshold Sh2 when the work implement 6 is in an unloaded state. The load applied to the power transmission device 22 when the direction of travel of the work machine 1 is changed when the work implement 6 is in a loaded state is greater than the load applied to the power transmission device 22 when the direction of travel of the work machine 1 is changed when the work implement 6 is in an unloaded state. By making the first speed threshold Sh1 in the loaded state smaller than the first speed threshold Sh1 in the unloaded state, when changing the direction of travel of the work machine 1 in the loaded state, the automatic brake will operate even if the travel speed of the work machine 1 is relatively low, thereby reducing the load on the power transmission device 22. By making the second speed threshold Sh2 in the loaded state smaller than the second speed threshold Sh2 in the unloaded state, the direction of travel of the work machine 1 will be changed after the travel speed of the work machine 1 has been sufficiently reduced by the automatic brake in the loaded state, thereby reducing the load on the power transmission device 22.

[0106] Second Embodiment A second embodiment will be described below. In the following description, components that are the same as or equivalent to those in the first embodiment described above will be denoted by the same reference numerals, and descriptions of those components will be simplified or omitted.

[0107] <Work machine operation> Figures 8 and 9 are each a diagram illustrating the operation of the work machine 1 according to the embodiment. At the work site 201, shuttle operation may be performed in which the forward / reverse switch lever 74 is operated while the work machine 1 is traveling. Shuttle operation includes operating the forward / reverse switch lever 74 to switch the traveling direction of the work machine 1 from forward to reverse while the work machine 1 is moving forward, and operating the forward / reverse switch lever 74 to switch the traveling direction of the work machine 1 from reverse to forward while the work machine 1 is moving backward. In shuttle operation, the forward / reverse switch lever 74 is operated to switch the traveling direction of the work machine 1 before the work machine 1 comes to a stop. By operating the forward / reverse switch lever 74 before the work machine 1 comes to a stop, the operator can quickly switch the traveling direction of the work machine 1.

[0108] As shown in Figures 8 and 9, there is a possibility that a slope exists at the work site 201. Shuttle operation may be performed on a slope. When the work machine 1 is descending a slope, the forward / reverse switch lever 74 may be operated to switch the work machine 1 from a state of descending a slope to a state of ascending a slope. Figure 8 shows a state in which the forward / reverse switch lever 74 is operated to switch the traveling direction of the work machine 1 from forward to reverse when the work machine 1 is descending a slope while moving forward. Figure 9 shows a state in which the forward / reverse switch lever 74 is operated to switch the traveling direction of the work machine 1 from reverse to forward when the work machine 1 is descending a slope while moving backward.

[0109] When performing a shuttle operation, the operator often operates the boom lever 75 and the bucket lever 76 so that the work implement 6 assumes a predetermined posture. The predetermined posture of the work implement 6 is a posture that allows the work machine 1 to travel stably at a high traveling speed.

[0110] The work implement 6 includes a boom 12 rotatably connected to the front frame 2F of the work machine 1 about a rotation axis AXa (first rotation axis), and a bucket 13 rotatably connected to the boom 12 about a rotation axis AXb (second rotation axis). If a line connecting the rotation axis CXf of the front wheels 5F and the rotation axis CXr of the rear wheels 5R when the work machine 1 is traveling in a straight line is defined as a prescribed line RL, the predetermined posture of the work implement 6 is a posture in which the rotation axis AXa and the rotation axis AXb are each positioned farther from the ground than the prescribed line RL. The ground is the traveling surface on which the work machine 1 travels, and includes the slope of a hill. Furthermore, the predetermined posture of the work implement 6 is a posture in which the rotation axis AXb is positioned closer to the prescribed line RL than the rotation axis AXa. The predetermined posture of the work implement 6 is a posture in which the bottom surface 13C of the bucket 13 is tilted forward and away from the specified line RL, and the bucket 13 is off the ground.

[0111] In the following description, when the work machine 1 is descending a slope with an inclination angle θ equal to or greater than a predetermined angle threshold Sha, and the direction of travel of the work machine 1 is changed so that the work machine 1 ascends the slope, this will be referred to as "slope shuttle operation" as appropriate. The inclination angle θ of a slope is the angle between the horizontal plane and the ground (slope) on which the work machine 1 is traveling. The inclination angle θ is less than 90°. An inclination angle θ of 0° means that the ground on which the work machine 1 is traveling is parallel to the horizontal plane. The greater the inclination angle θ, the steeper the slope.

[0112] 10 is a functional block diagram showing a control system 100 for a work machine 1 according to an embodiment. The control system 100 has an operation device 7, a remote controller 9, an on-board controller 30, an inclination sensor 25, a vehicle speed sensor 26, a work machine attitude sensor 28, a load sensor 27, and a camera 29.

[0113] The on-board controller 30 has a sensor data acquisition unit 101 , an operation signal acquisition unit 102 , a condition determination unit 103 , a travel control unit 104 , a work machine control unit 105 , a threshold setting unit 106 , and a transmission unit 107 .

[0114] The sensor data acquisition unit 101 acquires detection data from the inclination sensor 25, the vehicle speed sensor 26, the work implement attitude sensor 28, and the load sensor 27. The detection data from the work implement attitude sensor 28 includes detection data from the boom angle sensor 28A indicating the boom angle and detection data from the bucket angle sensor 28B indicating the bucket angle.

[0115] The operation signal acquisition unit 102 acquires operation signals from the operation device 7. The operation signals from the operation device 7 include an operation signal from an accelerator pedal 71 operated to increase the traveling speed of the work machine 1, an operation signal from a brake pedal 72 operated to decrease the traveling speed of the work machine 1, an operation signal from a steering wheel 73 operated to adjust the traveling direction of the work machine 1, an operation signal from a forward / reverse switch lever 74 operated to switch the traveling direction of the work machine 1, and an operation signal from a speed stage setting device 77 operated to set a transmission speed stage or a maximum traveling speed of the work machine 1. The operation signals from the operation device 7 also include an operation signal from a boom lever 75 operated to operate the boom 12, and an operation signal from a bucket lever 76 operated to operate the bucket 13.

[0116] The condition determination unit 103 determines whether the work machine 1 satisfies the slope shuttle operation conditions. The slope shuttle operation conditions include the forward / reverse switch lever 74 being operated to switch the traveling direction of the work machine 1 while the work machine 1 is descending a slope with an inclination angle θ equal to or greater than a predetermined angle threshold Sha. The condition determination unit 103 determines whether the operation signal from the forward / reverse switch lever 74 for switching the traveling direction of the work machine 1 while the work machine 1 is descending a slope with an inclination angle θ equal to or greater than the angle threshold Sha satisfies the acquired slope shuttle operation conditions. The angle threshold Sha is, for example, 5°.

[0117] The inclination angle of the vehicle body 2 of the work machine 1 is detected by the inclination sensor 25. The inclination sensor 25 detects the inclination angle of the vehicle body 2 with respect to the horizontal plane. The inclination angle of the vehicle body 2 with respect to the horizontal plane and the inclination angle θ of the slope can be considered to be the same. In this embodiment, the inclination angle θ of the slope is detected by the inclination sensor 25.

[0118] The detection data of the inclination sensor 25 is acquired by the sensor data acquisition unit 101. An operation signal from the forward / reverse switch lever 74 that is operated to switch the traveling direction of the work machine 1 is acquired by the operation signal acquisition unit 102. The condition determination unit 103 can determine whether the work machine 1 is descending a slope with an inclination angle θ that is equal to or greater than the angle threshold Sha, based on the detection data of the inclination sensor 25 acquired by the sensor data acquisition unit 101. The condition determination unit 103 can determine whether the traveling direction of the work machine 1 has been switched, based on the operation signal from the forward / reverse switch lever 74 acquired by the operation signal acquisition unit 102.

[0119] In this embodiment, the slope shuttle operation condition includes the work machine 1 descending a slope at a traveling speed equal to or greater than a predetermined first speed threshold Sh1. The condition determination unit 103 determines whether or not an operation signal has been acquired from the forward / reverse selector lever 74 for switching the traveling direction of the work machine 1 while the work machine 1 is descending a slope with an inclination angle θ equal to or greater than the angle threshold Sha at a traveling speed equal to or greater than the first speed threshold Sh1. The first speed threshold Sh1 is, for example, 10 km / h. The first speed threshold Sh1 is set to the same value as the traveling speed when the work machine 1 travels between work sites. The first speed threshold Sh1 may also be set to the maximum traveling speed when the upper limit of the speed range in a transmission having a torque converter is set to third or fourth gear.

[0120] The traveling speed of the work machine 1 is detected by the vehicle speed sensor 26. The detection data of the vehicle speed sensor 26 is acquired by the sensor data acquisition unit 101. The condition determination unit 103 can determine whether the work machine 1 is traveling at a traveling speed equal to or greater than the first speed threshold Sh1, based on the detection data of the vehicle speed sensor 26 acquired by the sensor data acquisition unit 101.

[0121] In the embodiment, the slope shuttle operation condition includes the posture of the work machine 6 being a predetermined posture. As described above, the predetermined posture of the work machine 6 is a posture in which the rotation axis AXa and the rotation axis AXb are each positioned farther from the ground than the specified line RL, the rotation axis AXb is positioned closer to the specified line RL than the rotation axis AXa, the bottom surface 13C of the bucket 13 is tilted forward and away from the specified line RL, and the bucket 13 is off the ground. The predetermined posture of the work machine 6 includes a posture in which the bucket 13 is off the ground, for example, by 10 cm or more.

[0122] The posture of the work implement 6 is detected by a work implement posture sensor 28. Detection data of the work implement posture sensor 28 is acquired by a sensor data acquisition unit 101. A condition determination unit 103 can determine whether or not the work implement 6 is in a predetermined posture based on the detection data of the work implement posture sensor 28 acquired by the sensor data acquisition unit 101.

[0123] The travel control unit 104 controls the travel of the work machine 1 based on operation signals from the travel system operation device 7A. Based on operation signals from the travel system operation device 7A, the travel control unit 104 adjusts the travel speed of the work machine 1, adjusts the travel direction of the work machine 1, and switches the work machine 1 between forward and reverse travel.

[0124] Furthermore, the traveling control unit 104 outputs control commands so that the power transmission device 22 and the brake device 23 each operate under predetermined conditions, regardless of the operation signal from the traveling system operation device 7A. Even if the forward / reverse switch lever 74 is operated, the traveling control unit 104 can output control commands so that the power transmission device 22 operates under predetermined conditions, regardless of the operation signal from the forward / reverse switch lever 74. Even if the brake pedal 72 is not operated, the traveling control unit 104 can output control commands so that the brake device 23 operates under predetermined conditions.

[0125] In the following description, the control command output from the travel control unit 104 to the power transmission device 22 to switch the direction of travel of the work machine 1 based on an operation signal from the forward / reverse switch lever 74 will be referred to as a manual forward / reverse switch command, as appropriate, and the control command output from the travel control unit 104 to the power transmission device 22 to switch the direction of travel of the work machine 1 regardless of the operation signal from the forward / reverse switch lever 74 will be referred to as an automatic forward / reverse switch command, as appropriate.

[0126] In the following description, a control command output from the travel control unit 104 to the brake device 23 to brake the work machine 1 based on an operation signal from the brake pedal 72 will be referred to as a manual brake command, as appropriate, and a control command output from the travel control unit 104 to the brake device 23 to brake the work machine 1 regardless of an operation signal from the brake pedal 72 will be referred to as an automatic brake command, as appropriate. Furthermore, the state in which the brake device 23 operates based on an automatic brake command will be referred to as automatic braking, as appropriate.

[0127] In this embodiment, when the condition determination unit 103 determines that the slope shuttle operation conditions are satisfied, the travel control unit 104 prohibits the output of an automatic forward / reverse switch command that switches the traveling direction of the work machine 1. When the condition determination unit 103 determines that the slope shuttle operation conditions are satisfied, the travel control unit 104 outputs an automatic brake command and an automatic forward / reverse switch command. When the condition determination unit 103 determines that the slope shuttle operation conditions are satisfied, the travel control unit 104 outputs an automatic brake command to the brake device 23 to reduce the traveling speed of the work machine 1, and then outputs an automatic forward / reverse switch command to the power transmission device 22 to switch the traveling direction of the work machine 1.

[0128] The travel control unit 104 outputs an automatic forward / reverse switch command after the travel speed of the work machine 1 drops to a predetermined second speed threshold Sh2 or below due to an automatic brake command. The second speed threshold Sh2 is a value smaller than the first speed threshold Sh1. The second speed threshold Sh2 is, for example, 5 km / h. The second speed threshold Sh2 is set to the same value as the travel speed when the work machine 1 is performing excavation work or loading work. The second speed threshold Sh2 may be set to the maximum travel speed when the upper limit of the speed stage in a transmission having a torque converter is set to second gear.

[0129] When the automatic brake command is output while the work machine 1 is descending a slope with a tilt angle θ equal to or greater than the angle threshold Sha at a traveling speed equal to or greater than the first speed threshold Sh1, the traveling speed of the work machine 1 decreases below the first speed threshold Sh1 and eventually decreases to or less than the second speed threshold Sh2. After the traveling speed of the work machine 1 decreases to or less than the second speed threshold Sh2, the cruise control unit 104 outputs an automatic forward / reverse switch command to the power transmission device 22 to switch the direction of travel of the work machine 1. After outputting the automatic forward / reverse switch command, the cruise control unit 104 stops outputting the automatic brake command. Stopping the output of the automatic brake command releases the operation of the brake device 23. Outputting the automatic forward / reverse switch command switches the direction of travel of the work machine 1 and causes the work machine 1 to climb the slope. Note that the cruise control unit 104 may start outputting the automatic forward / reverse switch command after the traveling speed of the work machine 1 decreases to or less than the second speed threshold Sh2 and before the operation of the brake device 23 is released.

[0130] When the work machine 1 is descending a slope with a slope angle θ that is equal to or greater than the angle threshold Sha, the travel control unit 104 may adjust the command value of the automatic brake command based on the slope inclination angle θ. The larger the command value of the automatic brake command, the stronger the braking force applied by the brake device 23, and the smaller the command value of the automatic brake command, the weaker the braking force applied by the brake device 23. In an embodiment, the larger the command value of the automatic brake command, the stronger the force pressing the brake pads against the brake rotor, and the smaller the command value of the automatic brake command, the weaker the force pressing the brake pads against the brake rotor. The travel control unit 104 may output the automatic brake command so that the braking force becomes stronger the greater the slope inclination angle θ. By adjusting the command value of the automatic brake command so that the braking force becomes stronger the greater the slope inclination angle θ, an increase in the travel speed of the work machine 1 due to the effect of gravity is suppressed.

[0131] When the work machine 1 is traveling down a slope at a traveling speed equal to or greater than the first speed threshold Sh1, the travel control unit 104 may adjust the command value of the automatic brake command based on the traveling speed of the work machine 1. The travel control unit 104 may output the automatic brake command so that the braking force increases the higher the traveling speed of the work machine 1. By adjusting the command value of the automatic brake command so that the braking force increases the higher the traveling speed of the work machine 1, the traveling speed of the work machine 1 becomes equal to or less than the second speed threshold Sh2 in a short period of time.

[0132] Note that when the work machine 1 is traveling at a traveling speed equal to or greater than the first speed threshold Sh1, there is a possibility that the operator will operate the forward / reverse switch lever 74 while operating the brake pedal 72. Even if the brake pedal 72 is operated, there is a possibility that the forward / reverse switch lever 74 will be operated before the traveling speed of the work machine 1 becomes less than the first speed threshold Sh1. Even if the brake pedal 72 is operated, the travel control unit 104 may output an automatic brake command regardless of an operation signal from the brake pedal 72. The travel control unit 104 may adjust the command value of the automatic brake command based on an operation signal from the brake pedal 72. The travel control unit 104 calculates a target brake command value so as to obtain a target braking force, and calculates a command value of a manual brake command based on an operation signal from the brake pedal 72. The travel control unit 104 calculates the difference between the target brake command value and the command value of the manual brake command as the command value of the automatic brake command. The traveling control unit 104 may output a brake command having a command value obtained by adding the command value of the manual brake command and the command value of the automatic brake command so as to obtain a target braking force.

[0133] It should be noted that while an automatic brake command is being output, there is a possibility that the operator will operate the accelerator pedal 71. Even if the accelerator pedal 71 is operated, the cruise control unit 104 outputs the automatic brake command regardless of the operation signal from the accelerator pedal 71. Furthermore, if the accelerator pedal 71 is operated while an automatic brake command is being output, the cruise control unit 104 may output the automatic brake command regardless of the operation signal from the accelerator pedal 71, and may also output a control command to reduce the output (rotation speed) of the engine 20.

[0134] The work machine control unit 105 controls the work machine 6 based on an operation signal from the work machine operating device 7B. The work machine control unit 105 controls the boom control valve 38 based on an operation signal from the boom lever 75. By controlling the boom control valve 38, the boom cylinder 18 extends and retracts, and the boom 12 performs a raising and lowering operation. The work machine control unit 105 controls the bucket control valve 39 based on an operation signal from the bucket lever 76. By controlling the bucket control valve 39, the bucket cylinder 19 extends and retracts, and the bucket 13 performs a tilting operation and a dumping operation.

[0135] The threshold setting unit 106 changes the first speed threshold Sh1 based on the detection data of the inclination sensor 25. The threshold setting unit 106 reduces the first speed threshold Sh1 the greater the inclination angle θ of the slope detected by the inclination sensor 25. If the slope is steep, it is determined that the slope shuttle operation conditions are satisfied even if the traveling speed of the work machine 1 is low. For example, if the inclination angle θ of the slope is 5° or more and 7° or less, the first speed threshold Sh1 is set to 10 km / h, and if the inclination angle θ of the slope is 8° or more, the first speed threshold Sh1 is set to 8 km / h.

[0136] The threshold setting unit 106 changes the second speed threshold Sh2 based on the detection data of the inclination sensor 25. The threshold setting unit 106 reduces the second speed threshold Sh2 the greater the inclination angle θ of the slope detected by the inclination sensor 25. If the slope is steep, an automatic forward / reverse switching command is output after the traveling speed of the work machine 1 has sufficiently decreased. For example, if the inclination angle θ of the slope is 5° or more and 7° or less, the second speed threshold Sh2 is set to 5 km / h, and if the inclination angle θ of the slope is 8° or more, the second speed threshold Sh2 is set to 3 km / h.

[0137] The threshold setting unit 106 may change the first speed threshold Sh1 based on the detection data of the load sensor 27. The threshold setting unit 106 can determine whether the work machine 6 is in a loaded state or an unloaded state based on the detection data of the load sensor 27. The threshold setting unit 106 sets the first speed threshold Sh1 when the work machine 6 is in a loaded state to be smaller than the first speed threshold Sh1 when the work machine 6 is in an unloaded state. When the work machine 6 is in a loaded state, it is determined that the slope shuttle operation condition is satisfied even if the traveling speed of the work machine 1 is low. For example, if the first speed threshold Sh1 when the work machine 6 is in an unloaded state is 10 km / h, the first speed threshold Sh1 when the work machine 6 is in a loaded state is set to 8 km / h.

[0138] The threshold setting unit 106 may change the second speed threshold Sh2 based on the detection data of the load sensor 27. The threshold setting unit 106 can determine whether the work implement 6 is in a loaded state or an unloaded state based on the detection data of the load sensor 27. The threshold setting unit 106 sets the second speed threshold Sh2 when the work implement 6 is in a loaded state to be smaller than the second speed threshold Sh2 when the work implement 6 is in an unloaded state. When the work implement 6 is in a loaded state, an automatic forward / reverse switching command is output after the traveling speed of the work machine 1 has sufficiently decreased. For example, if the second speed threshold Sh2 when the work implement 6 is in an unloaded state is 5 km / h, the second speed threshold Sh2 when the work implement 6 is in a loaded state is set to 3 km / h.

[0139] The transmission unit 107 transmits image data captured by the camera 29 to the remote controller 9. The transmission unit 107 may also transmit detection data of the work machine attitude sensor 28 to the remote controller 9.

[0140] <Construction machine control method> Figure 11 is a flowchart showing a control method for the construction machine 1 according to the embodiment. The operation signal acquisition unit 102 acquires an operation signal from the operation device 7. The travel control unit 104 controls the travel of the construction machine 1 based on an operation signal from the traveling system operation device 7A. The work implement control unit 105 controls the construction machine 6 based on an operation signal from the work implement operation device 7B. The sensor data acquisition unit 101 acquires detection data from the inclination sensor 25, detection data from the vehicle speed sensor 26, detection data from the work implement attitude sensor 28, and detection data from the load sensor 27 (step S1).

[0141] The threshold setting unit 106 sets the first speed threshold Sh1 and the second speed threshold Sh2 based on one or both of the detection data of the inclination sensor 25 and the detection data of the cargo sensor 27 .

[0142] The condition determination unit 103 determines whether or not the slope shuttle operation conditions are satisfied based on detection data from the inclination sensor 25, which detects the slope inclination angle θ, detection data from the vehicle speed sensor 26, which detects the traveling speed of the work machine 1, and the operation signal from the forward / reverse switch lever 74. In other words, the condition determination unit 103 determines whether or not the operation signal acquisition unit 102 has acquired an operation signal from the forward / reverse switch lever 74 to switch the traveling direction of the work machine 1, which is traveling down a slope with an inclination angle θ that is equal to or greater than the angle threshold Sha, at a traveling speed that is equal to or greater than the first speed threshold Sh1 (step S2).

[0143] In step S2, if it is determined that the slope shuttle operation conditions are satisfied (step S2: Yes), the travel control unit 104 outputs an automatic brake command to the brake device 23 to reduce the travel speed of the work machine 1, while prohibiting the output of an automatic forward / reverse switching command to switch the direction of travel of the work machine 1 (step S3).

[0144] After outputting the automatic brake command, the travel control unit 104 determines whether the travel speed of the work machine 1 has decreased to or below the second speed threshold Sh2 based on the detection data of the vehicle speed sensor 26 (step S4).

[0145] In step S4, if it is determined that the traveling speed of the work machine 1 has not decreased to or below the second speed threshold Sh2 (step S4: No), the traveling control unit 104 continues to output the automatic brake command.

[0146] If it is determined in step S4 that the traveling speed of the work machine 1 has fallen to or below the second speed threshold Sh2 (step S4: Yes), the travel control unit 104 stops outputting the automatic brake command. By stopping the output of the automatic brake command, operation of the brake device 23 is released. After the traveling speed of the work machine 1 has fallen to or below the second speed threshold Sh2, the travel control unit 104 outputs an automatic forward / reverse switch command to the power transmission device 22 to switch the traveling direction of the work machine 1 (step S5). By outputting the automatic forward / reverse switch command, the traveling direction of the work machine 1 is switched. The work machine 1 starts to climb the slope.

[0147] If it is determined in step S2 that the slope shuttle operation conditions are not satisfied, that is, if an operation signal is acquired from the forward / reverse switch lever 74 to switch the traveling direction of the work machine 1 but the inclination angle θ of the slope is less than the angle threshold value Sha or the traveling speed of the work machine 1 is less than the first speed threshold value Sh1 (step S2: No), the travel control unit 104 outputs a manual forward / reverse switch command to the power transmission device 22 without outputting an automatic brake command (step S6). By outputting the manual forward / reverse switch command, the traveling direction of the work machine 1 is switched.

[0148] Figure 12 is a timing chart showing a control method for the work machine 1 according to the embodiment. In the following description, it is assumed that the power transmission device 22 has a forward clutch, a reverse clutch, and a torque converter. The work machine 1 moves forward when the forward clutch is engaged. The work machine 1 moves backward when the reverse clutch is engaged. Furthermore, in the following description, a control command for moving the work machine 1 forward will be referred to as a forward command, as appropriate, and a control command for moving the work machine 1 backward will be referred to as a reverse command, as appropriate. The forward command is a control command for engaging the forward clutch. The reverse command is a control command for engaging the reverse clutch.

[0149] 12, the horizontal axis represents time, and the vertical axis represents the travel speed of the work machine 1, the inclination angle θ of the slope, the operation signal from the forward / reverse selector lever 74, the command value of the forward command output from the travel control unit 104 to the forward clutch and the clutch pressure of the forward clutch, the command value of the reverse command output from the travel control unit 104 to the reverse clutch and the clutch pressure of the reverse clutch, and the command value and braking force of the automatic brake command output from the travel control unit 104 to the brake device 23.

[0150] 12 shows a state in which the work machine 1 is moving forward from time t0 at a traveling speed Ts while descending a slope. When the operation signal from the forward / reverse selector lever 74 is an operation signal Sf that moves the work machine 1 forward, the travel control unit 104 outputs a forward command of command value Vf to the forward clutch based on the operation signal Sf. When the forward command is output, the forward clutch is engaged at a predetermined clutch pressure Pf. Engaging the forward clutch causes the work machine 1 to move forward.

[0151] At time t1, the forward / reverse selector lever 74 is operated. At time t1, the operation signal from the forward / reverse selector lever 74 switches from the operation signal Sf that moves the work machine 1 forward to the operation signal Sr that moves the work machine 1 backward. At time t1, the inclination angle θ of the slope is equal to or greater than the angle threshold Sha. Note that in FIG. 12, the inclination angle θ of the downhill slope is shown as a negative value, and the inclination angle θ being equal to or greater than the angle threshold Sha means that the absolute value of the inclination angle θ is equal to or greater than the absolute value of the angle threshold Sha. Also, at time t1, the traveling speed Ts of the work machine 1 is equal to or greater than the first speed threshold Sh1. Therefore, the condition determination unit 103 determines that the slope shuttle operation condition is satisfied at time t1.

[0152] Because it is determined that the hill shuttle operation condition is satisfied at time t1, the cruise control unit 104 outputs an automatic brake command of command value Vb to reduce the traveling speed Ts of the work machine 1. The cruise control unit 104 continues to output the automatic brake command until the traveling speed Ts of the work machine 1 becomes equal to or less than the second speed threshold Sh2. In the example shown in Figure 12, at time t2, the traveling speed Ts of the work machine 1 decreases to the second speed threshold Sh2.

[0153] In this embodiment, the traveling control unit 104 gradually increases the command value Vb of the automatic brake command from time t1. Because the command value Vb gradually increases, the braking force Fb by the brake device 23 gradually increases. Because the command value Vb gradually increases, the automatic brake is prevented from suddenly operating.

[0154] The travel control unit 104 does not output an automatic forward / reverse switch command until the travel speed Ts of the work machine 1 becomes equal to or less than the second speed threshold Sh2. The forward command continues to be output during the period between time t1 and time t2, and the forward clutch is maintained engaged.

[0155] If, at time t2, it is determined that the traveling speed Ts of the work machine 1 has become equal to or less than the second speed threshold Sh2, the traveling control unit 104 gradually decreases the command value Vb of the automatic brake command. The command value Vb of the automatic brake command gradually decreases from time t2. Because the command value Vb gradually decreases, the braking force Fb by the brake device 23 gradually decreases. Because the command value Vb gradually decreases, the automatic brake is prevented from being suddenly released. Note that in this embodiment, when the braking force by the brake device 23 weakens, the braking force by the torque converter becomes dominant. Because the braking force by the torque converter gradually weakens, the automatic brake is prevented from being suddenly released.

[0156] At time t2, the travel control unit 104 stops outputting the forward command and outputs a reverse command of command value Vr to the reverse clutch. When the reverse command is output, the reverse clutch is engaged at a predetermined clutch pressure Pr. When the reverse clutch is engaged, the work machine 1 moves backward. In other words, the work machine 1 starts to climb the slope. When the forward clutch is disengaged, the clutch pressure Pf of the forward clutch gradually decreases. When the reverse clutch is engaged, the clutch pressure Pr of the reverse clutch gradually increases.

[0157] <Effects> As described above, in the embodiment, the control system 100 of the work machine 1 includes an on-board controller 30. The on-board controller 30 has an operation signal acquisition unit 102 that acquires an operation signal from the forward / reverse switch lever 74, which is an operating device that is operated to switch the traveling direction of the work machine 1, a condition determination unit 103 that determines whether the operation signal from the forward / reverse switch lever 74 for switching the traveling direction of the work machine 1 when the work machine 1 is descending a slope with an inclination angle θ that is equal to or greater than the angle threshold Sha satisfies the acquired slope shuttle operation condition, and a travel control unit 104 that prohibits the output of an automatic forward / reverse switch command to switch the traveling direction of the work machine 1 when it is determined that the slope shuttle operation condition is satisfied.

[0158] According to this embodiment, even if the forward / reverse selector lever 74 is operated during shuttle operation while the work machine 1 is descending a steep slope, the direction of travel of the work machine 1 is prohibited from being changed. This prevents deterioration of the power transmission device 22.

[0159] In this embodiment, the travel control unit 104 outputs an automatic brake command to reduce the travel speed of the work machine 1, and then outputs an automatic forward / reverse switch command to switch the direction of travel of the work machine 1. According to this embodiment, if the forward / reverse switch lever 74 is operated during shuttle operation while the work machine 1 is descending a steep slope, the automatic brake is activated before the power transmission device 22 is activated. After the travel speed of the work machine 1 is reduced by activation of the automatic brake, the power transmission device 22 is activated so as to switch the direction of travel of the work machine 1. Because the power transmission device 22 is activated after the travel speed of the work machine 1 is reduced by the automatic brake, the load on the power transmission device 22 is reduced. This reduces deterioration of the power transmission device 22.

[0160] When the work machine 1 is descending a steep slope, the travel speed of the work machine 1 increases due to the action of gravity, and there is a possibility that the rotating members of the power transmission device 22, such as the clutch, will rotate at a high rotational speed. When the work machine 1 is descending a slope while moving forward, there is a possibility that the rotating members of the power transmission device 22 will rotate at a high rotational speed in the forward direction, and when the work machine 1 is descending a slope while moving backward, there is a possibility that the rotating members of the power transmission device 22 will rotate at a high rotational speed in the reverse direction. For example, when the work machine 1 is descending a steep slope while moving forward, if the power transmission device 22 operates to switch the traveling direction of the work machine 1 based on an operation signal from the forward / reverse selector lever 74, the rotating members that are rotating in the forward direction at a high rotational speed will suddenly rotate in the reverse direction. This may result in a high load being placed on the rotating members.

[0161] According to this embodiment, after the travel speed of the work machine 1 is reduced by activation of the automatic brake, the power transmission device 22 operates to switch the traveling direction of the work machine 1. In other words, after the rotational speed of the rotating member rotating in the forward direction is reduced, the rotating member is rotated in the reverse direction. This prevents a high load from being applied to the rotating member. This therefore prevents deterioration of the power transmission device 22.

[0162] When the work machine 1 is remotely operated, it is difficult for the operator in the remote control room 202 to sense that the work machine 1 is descending a steep slope. For this reason, there is a possibility that the operator will unconsciously operate the forward / reverse switch lever 74 while the work machine 1 is descending a steep slope. According to the embodiment, if the forward / reverse switch lever 74 is operated while the work machine 1 is descending a steep slope, the automatic brake is activated and then the direction of travel of the work machine 1 is changed. As a result, deterioration of the work machine 1 is suppressed.

[0163] The hill shuttle operation condition includes the work machine 1 traveling down a slope at a traveling speed equal to or greater than the first speed threshold Sh1. During shuttle operation, if the forward / reverse switch lever 74 is operated while the work machine 1 is traveling at a high traveling speed, the automatic brake is activated before the power transmission device 22 is activated. After the traveling speed of the work machine 1 is reduced by the activation of the automatic brake, the power transmission device 22 is activated so as to switch the direction of travel of the work machine 1. Because the power transmission device 22 is activated after the traveling speed of the work machine 1 is reduced by the automatic brake, the load on the power transmission device 22 is reduced. As a result, deterioration of the power transmission device 22 is suppressed.

[0164] The travel control unit 104 outputs an automatic forward / reverse switch command after the travel speed of the work machine 1 has fallen to or below the second speed threshold Sh2 due to an automatic brake command. After the automatic brake is activated and the travel speed of the work machine 1 has fallen sufficiently, the direction of travel of the work machine 1 is switched. This prevents deterioration of the work machine 1.

[0165] The travel control unit 104 stops outputting the automatic brake command after the travel speed of the work machine 1 drops below the second speed threshold Sh2. For example, after the travel speed of the work machine 1 moving forward drops below the second speed threshold Sh2, the output of the automatic brake command is stopped, allowing the work machine 1 to smoothly start reversing.

[0166] The slope shuttle operation conditions include a predetermined posture in which the pivot axis AXa and the pivot axis AXb are each positioned farther from the ground than the specified line RL, the pivot axis AXb is positioned closer to the specified line RL than the pivot axis AXa, the bottom surface 13C of the bucket 13 is tilted forward away from the specified line RL, and the bucket 13 is off the ground. Because the work implement 6 is in the predetermined posture, the work machine 1 can travel stably at a high traveling speed. If the slope shuttle operation conditions do not include the predetermined posture of the work implement 6, the work efficiency of the work machine 1 may decrease. For example, if the automatic brake is activated when the work machine 1 changes its traveling direction while in a raised posture in which the boom 12 is raised, the weight balance of the work machine 1 may be disrupted. If the automatic brake is activated when the work machine 1 changes its traveling direction while in an excavation posture in which the bucket 13 is in contact with the ground, this will affect the excavation operation. Because the slope shuttle operation conditions include the predetermined posture of the work implement 6, a decrease in the work efficiency of the work machine 1 is suppressed.

[0167] The threshold setting unit 106 changes the first speed threshold Sh1 and the second speed threshold Sh2 based on detection data from the inclination sensor 25 that detects the inclination angle θ of the slope. The threshold setting unit 106 reduces the first speed threshold Sh1 and the second speed threshold Sh2 the greater the inclination angle θ of the slope. The load applied to the power transmission device 22 when changing the traveling direction of the work machine 1 when the inclination angle θ of the slope is large is greater than the load applied to the power transmission device 22 when changing the traveling direction of the work machine 1 when the inclination angle θ of the slope is small. By reducing the first speed threshold Sh1 the greater the inclination angle θ of the slope, when changing the traveling direction of the work machine 1 going down a steep slope, the automatic brake will be activated even if the traveling speed of the work machine 1 is relatively low, and the load applied to the power transmission device 22 will be reduced. By making the second speed threshold Sh2 smaller the greater the inclination angle θ of the slope, when the slope is steep, the automatic brake will sufficiently reduce the running speed of the work machine 1 before the direction of travel of the work machine 1 is changed, thereby reducing the load on the power transmission device 22.

[0168] The threshold setting unit 106 changes the first speed threshold Sh1 and the second speed threshold Sh2 based on detection data from the load sensor 27 that detects the weight of the work implement 6. The threshold setting unit 106 sets the first speed threshold Sh1 when the work implement 6 is in a loaded state to be smaller than the first speed threshold Sh1 when the work implement 6 is in an unloaded state. The threshold setting unit 106 sets the second speed threshold Sh2 when the work implement 6 is in a loaded state to be smaller than the second speed threshold Sh2 when the work implement 6 is in an unloaded state. The load applied to the power transmission device 22 when the direction of travel of the work machine 1 is changed when the work implement 6 is in a loaded state is greater than the load applied to the power transmission device 22 when the direction of travel of the work machine 1 is changed when the work implement 6 is in an unloaded state. By making the first speed threshold Sh1 in the loaded state smaller than the first speed threshold Sh1 in the unloaded state, when changing the direction of travel of the work machine 1 in the loaded state, the automatic brake will operate even if the travel speed of the work machine 1 is relatively low, thereby reducing the load on the power transmission device 22. By making the second speed threshold Sh2 in the loaded state smaller than the second speed threshold Sh2 in the unloaded state, the direction of travel of the work machine 1 will be changed after the travel speed of the work machine 1 has been sufficiently reduced by the automatic brake in the loaded state, thereby reducing the load on the power transmission device 22.

[0169] [Other Embodiments] In the first and second embodiments described above, if the power transmission device 22 is a hydrostatic continuously variable transmission (HST), instead of switching between engagement of the forward clutch and engagement of the reverse clutch, switching of the discharge direction of the hydraulic pump is suspended and an automatic brake command is output from the travel control unit 104. If the power transmission device 22 has a motor, at least a portion of the deceleration force of the motor may be used for the automatic brake.

[0170] In the first and second embodiments described above, when an automatic brake command is output, notification data indicating that the automatic brake has been activated may be output from the display device 8 .

[0171] In the first and second embodiments described above, the load sensor 27 detecting the load state of the work implement 6 includes a weight sensor detecting the weight of the work implement 6. The load sensor 27 may include, for example, a camera capturing an image of the bucket 13. The camera can capture an image of the excavated material held in the bucket 13. Image data of the excavated material captured by the camera is transmitted to the on-board controller 30. Density data indicating the density of the excavated material is pre-stored in the on-board controller 30. The sensor data acquisition unit 101 of the on-board controller 30 estimates the volume of the excavated material held in the bucket 13 based on the image data of the excavated material. The sensor data acquisition unit 101 can calculate the weight of the excavated material held in the bucket 13 based on the estimated volume and the density data of the excavated material. Note that the three-dimensional shape of the excavated material may be detected by a three-dimensional sensor such as a laser scanner or a stereo camera. The sensor data acquisition unit 101 may estimate the volume of the excavated material held in the bucket 13 based on the three-dimensional shape of the excavated material.

[0172] In the second embodiment described above, tilt data indicating the tilt angle of the body 2 of the work machine 1 is detected by the tilt sensor 25. If the body 2 is equipped with a GNSS receiver that detects the position (absolute position) of the body 2 using a Global Navigation Satellite System (GNSS), the condition determination unit 103 may calculate the tilt angle θ of the slope that the work machine 1 is descending based on height data of the body 2 and horizontal movement data of the body 2 detected by the GNSS receiver. If the topographical data of the work site is known, the condition determination unit 103 may calculate the tilt angle θ of the slope that the work machine 1 is descending based on the known topographical data.

[0173] In the second embodiment described above, the slope shuttle operation condition does not have to include the work machine 1 traveling down a slope at a traveling speed equal to or greater than the first speed threshold Sh1. The slope shuttle operation condition does not have to include the work implement 6 being in a predetermined attitude.

[0174] In the first and second embodiments described above, some or all of the functions of the in-vehicle controller 30 may be provided in the remote controller 9. For example, the condition determination unit 103 and the threshold setting unit 106 may be provided in the remote controller 9.

[0175] In the first and second embodiments described above, the work machine 1 does not have to be remotely controlled. An operator may operate the work machine 1 by getting into the cab 4 of the work machine 1.

[0176] In the first and second embodiments described above, the work machine 1 is a wheel loader. However, the work machine 1 may be a wheel excavator, a motor grader, or a forklift.

[0177] [Supplementary Notes] The present disclosure may also adopt the following configurations. (Supplementary Note 1) A work machine control system comprising a controller, wherein the controller acquires an operation signal for switching the traveling direction of a work machine, determines whether the operation signal satisfies the acquired operating condition while the work machine is traveling at a traveling speed equal to or greater than a first speed threshold, and prohibits output of a forward / reverse switch command for switching the traveling direction if it is determined that the operating condition is satisfied. (Supplementary Note 2) The work machine control system described in (Supplementary Note 1), wherein the controller outputs a brake command to reduce the traveling speed of the work machine, and then outputs the forward / reverse switch command if it is determined that the operating condition is satisfied. (Supplementary Note 3) The work machine control system described in (Supplementary Note 2), wherein the controller outputs the forward / reverse switch command after the traveling speed of the work machine has decreased to below a second speed threshold that is lower than the first speed threshold due to the brake command. (Supplementary Note 4) The work machine control system described in (Supplementary Note 3), wherein the controller stops outputting the brake command after the travel speed of the work machine drops below a second speed threshold. (Supplementary Note 5) The work machine has a work implement including a boom rotatably connected to a body of the work machine about a first rotation axis, and a bucket rotatably connected to the boom about a second rotation axis, and the operating conditions include a predetermined attitude in which the second rotation axis is positioned below the first rotation axis, the bottom surface of the bucket is inclined upward toward the front, and the bucket is off the ground. (Supplementary Note 6) The work machine control system described in any one of (Supplementary Note 1) to (Supplementary Note 5), wherein the controller changes the first speed threshold based on detection data of a load sensor that detects the weight of a work implement provided on the work machine. (Supplementary Note 7) The work machine control system described in (Supplementary Note 6), wherein the controller changes the first speed threshold based on detection data of a load sensor that detects the weight of the work implement provided on the work machine.(Supplementary Note 8) The work machine control system described in (Supplementary Note 6), wherein the controller determines whether the work implement is loaded or unloaded based on detection data from the load sensor, and sets a first speed threshold when the work implement is loaded lower than the first speed threshold when the work implement is unloaded. (Supplementary Note 9) The work machine control system described in (Supplementary Note 3) or (Supplementary Note 4), wherein the controller changes a second speed threshold based on detection data from a load sensor that detects the weight of a work implement carried by the work machine. (Supplementary Note 10) The work machine control system described in (Supplementary Note 9), wherein the controller determines whether the work implement is loaded or unloaded based on detection data from the load sensor, and sets a second speed threshold when the work implement is loaded lower than the second speed threshold when the work implement is unloaded. (Supplementary Note 11) A work machine comprising: an operating device arranged outside the work machine; and the work machine control system described in any one of (Supplementary Note 1) to (Supplementary Note 10). (Supplementary Note 12) A work machine remote operation system comprising: an operating device arranged outside the work machine; and the work machine control system described in any one of (Supplementary Note 1) to (Supplementary Note 10). (Supplementary Note 13) A work machine control method, in which a controller executes the following steps: acquires an operation signal for switching the direction of travel of the work machine, determines whether the operation signal satisfies the acquired operating conditions while the work machine is traveling at a traveling speed equal to or greater than a first speed threshold, and prohibits the output of a forward / reverse switch command for switching the direction of travel if it is determined that the operating conditions are satisfied. (Supplementary Note 14) A work machine control system, comprising: a controller; acquires an operation signal for switching the direction of travel of the work machine, determines whether the operation signal satisfies the acquired operating conditions while the work machine is descending a slope with an inclination angle equal to or greater than an angle threshold, and prohibits the output of a forward / reverse switch command for switching the direction of travel if it is determined that the operating conditions are satisfied.(Supplementary Note 15) The work machine control system described in (Supplementary Note 14), wherein, when it is determined that the operating condition is satisfied, the controller outputs a brake command to reduce the traveling speed of the work machine, and then outputs a forward / reverse switch command to switch the traveling direction. (Supplementary Note 16) The work machine control system described in (Supplementary Note 15), wherein the operating condition includes the work machine traveling down the slope at a traveling speed equal to or greater than a first speed threshold. (Supplementary Note 17) The work machine control system described in (Supplementary Note 16), wherein the controller outputs the forward / reverse switch command after the traveling speed of the work machine has decreased to or below a second speed threshold that is smaller than the first speed threshold due to the brake command. (Supplementary Note 18) The work machine control system described in any one of (Supplementary Note 14) to (Supplementary Note 17), wherein the work machine has a work implement including a boom rotatably connected to a body of the work machine about a first pivot axis and a bucket rotatably connected to the boom about a second pivot axis, and front and rear wheels, and when a line connecting the rotation axis of the front wheel and the rotation axis of the rear wheel when the work machine is traveling in a straight line is defined as a prescribed line, the operating conditions include that the first pivot axis and the second pivot axis are each located at a position farther from the ground than the prescribed line, the second pivot axis is located at a position closer to the prescribed line than the first pivot axis, the bottom surface of the bucket is inclined forward and away from the prescribed line, and the bucket is in a predetermined posture where it is off the ground. (Supplementary Note 19) The work machine control system described in any one of (Supplementary Note 16) to (Supplementary Note 18), wherein the controller changes the first speed threshold based on inclination data that indicates the inclination angle of the body of the work machine. (Supplementary Note 20) The work machine control system described in any one of (Supplementary Note 17) to (Supplementary Note 19), wherein the controller changes the second speed threshold based on inclination data that indicates the inclination angle of the body of the work machine. (Supplementary Note 21) The work machine control system described in any one of (Supplementary Note 16) to (Supplementary Note 20), wherein the controller changes the first speed threshold based on detection data of a load sensor that detects the load state of a work implement that the work machine has.(Supplementary Note 22) The work machine control system described in (Supplementary Note 21), wherein the load sensor includes a weight sensor that detects the weight of the work machine. (Supplementary Note 23) The work machine control system described in (Supplementary Note 21) or (Supplementary Note 22), wherein the controller determines whether the work machine is loaded or unloaded based on detection data from the load sensor, and sets a first speed threshold when the work machine is loaded lower than the first speed threshold when the work machine is unloaded. (Supplementary Note 24) The work machine control system described in any one of (Supplementary Note 17) to (Supplementary Note 23), wherein the controller changes a second speed threshold based on detection data from a load sensor that detects the load state of a work machine possessed by the work machine. (Supplementary Note 25) The work machine control system described in (Supplementary Note 24), wherein the controller determines whether the work machine is loaded or unloaded based on detection data from the load sensor, and sets a second speed threshold when the work machine is loaded lower than the second speed threshold when the work machine is unloaded. (Supplementary Note 26) A work machine comprising the work machine control system set forth in any one of (Supplementary Note 14) to (Supplementary Note 25). (Supplementary Note 27) A work machine remote operation system comprising: an operating device arranged outside the work machine, and the work machine control system set forth in any one of (Supplementary Note 14) to (Supplementary Note 25). (Supplementary Note 28) A work machine control method, comprising: a controller acquiring an operation signal for switching the direction of travel of the work machine, determining whether the operation signal satisfies the acquired operating condition while the work machine is descending a slope with an inclination angle equal to or greater than an angle threshold, and prohibiting output of a forward / reverse switch command to switch the direction of travel if it is determined that the operating condition is satisfied.

[0178] 1...working machine, 2...body, 2F...front frame, 2R...rear frame, 3...articulating mechanism, 4...cab, 5...wheels, 5F...front wheels, 5R...rear wheels, 6...working machine, 7...operating device, 7A...traveling system operating device, 7B...working machine operating device, 8...display device, 9...remote controller, 10...operating seat, 11...articulating cylinder, 12...boom, 13...bucket, 13A...blade tip, 13B...opening, 13C...bottom, 14...bell run 15...bucket link, 16...bracket, 17...bracket, 18...boom cylinder, 19...bucket cylinder, 20...engine, 21...power take-off, 22...power transmission device, 23...brake device, 24A...steering pump, 24B...work implement pump, 25...inclination sensor, 26...vehicle speed sensor, 27...load sensor, 28...work implement attitude sensor, 28A...boom angle sensor, 28B...bucket angle sensor, 29...camera, 30...on-vehicle controller, 31...processor, 32...main memory, 33...storage, 34...input / output interface, 35...communication interface, 37...steering control valve, 38...boom control valve, 39...bucket control valve, 71...accelerator pedal, 72...brake pedal, 73...steering wheel, 74...forward / reverse switch lever, 75...boom lever, 76...bucket lever, 77...speed stage setting device, 100...control system, 101...sensor device Data acquisition unit, 102...operation signal acquisition unit, 103...condition determination unit, 104...travel control unit, 105...work machine control unit, 106...threshold setting unit, 107...transmission unit, 200...remote operation system, 201...work site, 202...remote operation room, 203...communication system, 700...operation device, AXa...rotation axis (first rotation axis), AXb...rotation axis (second rotation axis), AXc...rotation axis, AXd...rotation axis, AXe...rotation axis, AXf...rotation axis, CXf...rotation axis, CXr...rotation axis.

Claims

1. A control system for a work machine comprising a controller, which acquires an operation signal for switching the direction of travel of a work machine, determines whether the operation signal satisfies the acquired operating condition while the work machine is traveling at a speed equal to or greater than a first speed threshold, and prohibits the output of a forward / reverse switch command for switching the direction of travel if it is determined that the operating condition is satisfied.

2. A work machine control system as set forth in claim 1, wherein, when it is determined that the operating conditions are satisfied, the controller outputs a brake command to reduce the travel speed of the work machine, and then outputs the forward / reverse switch command.

3. A work machine control system according to claim 2, wherein the controller outputs the forward / reverse switch command after the travel speed of the work machine has decreased to or below a second speed threshold value that is lower than the first speed threshold value due to the brake command.

4. A work machine control system according to claim 3, wherein the controller stops outputting the brake command after the travel speed of the work machine drops below a second speed threshold.

5. A control system for a work machine as described in claim 1, wherein the work machine has a working implement including a boom rotatably connected to the body of the work machine around a first rotation axis, and a bucket rotatably connected to the boom around a second rotation axis, and the operating conditions include a predetermined attitude in which the second rotation axis is positioned below the first rotation axis, the bottom surface of the bucket is inclined upward toward the front, and the bucket is off the ground.

6. A work machine control system according to claim 1, wherein the controller changes the first speed threshold based on detection data from a load sensor that detects the load state of a work implement provided on the work machine.

7. A work machine control system according to claim 6, wherein the load sensor includes a weight sensor that detects the weight of the work machine.

8. A work machine control system as described in claim 6, wherein the controller determines whether the work machine is in a loaded state or an unloaded state based on detection data from the load sensor, and sets a first speed threshold when the work machine is in the loaded state to be smaller than the first speed threshold when the work machine is in the unloaded state.

9. A work machine control system according to claim 3, wherein the controller changes the second speed threshold based on detection data from a load sensor that detects the load state of a work implement provided on the work machine.

10. A work machine control system as described in claim 9, wherein the controller determines whether the work machine is loaded or unloaded based on the detection data of the load sensor, and sets the second speed threshold when the work machine is loaded to a value smaller than the second speed threshold when the work machine is unloaded.

11. A work machine comprising the work machine control system according to claim 1.

12. A remote operation system for a work machine, comprising: an operation device disposed outside the work machine; and the work machine control system according to claim 1.

13. A control method for a work machine, in which a controller executes the following steps: acquires an operation signal for switching the direction of travel of the work machine; determines whether the operation signal satisfies the acquired operating condition while the work machine is traveling at a traveling speed equal to or greater than a first speed threshold; and prohibits output of a forward / reverse switch command for switching the direction of travel if it is determined that the operating condition is satisfied.

14. A control system for a work machine, comprising: a controller that acquires an operation signal for switching the direction of travel of the work machine; determines whether or not the operation signal satisfies the acquired operating condition when the work machine is descending a slope with an inclination angle equal to or greater than an angle threshold; and prohibits output of a forward / reverse switch command for switching the direction of travel if it is determined that the operating condition is satisfied.

15. A work machine control system as set forth in claim 14, wherein, when it is determined that the operating conditions are satisfied, the controller outputs a brake command to reduce the travel speed of the work machine, and then outputs a forward / reverse switch command to switch the traveling direction.

16. A work machine control system according to claim 15, wherein the operating conditions include the work machine traveling down the slope at a travel speed equal to or greater than a first speed threshold.

17. A work machine control system according to claim 16, wherein the controller outputs the forward / reverse switch command after the travel speed of the work machine has decreased to or below a second speed threshold value that is lower than the first speed threshold value due to the brake command.

18. A control system for a work machine as described in claim 14, wherein the work machine has a work implement including a boom rotatably connected to the body of the work machine around a first pivot axis and a bucket rotatably connected to the boom around a second pivot axis, and front and rear wheels, and when the line connecting the rotation axis of the front wheel and the rotation axis of the rear wheel when the work machine is traveling in a straight line is defined as a prescribed line, the operating conditions include that the first pivot axis and the second pivot axis are each positioned at a position farther from the ground than the prescribed line, the second pivot axis is positioned at a position closer to the prescribed line than the first pivot axis, the bottom surface of the bucket is inclined forward and away from the prescribed line, and the bucket is in a predetermined attitude where it is off the ground.

19. A work machine control system according to claim 16, wherein the controller changes the first speed threshold based on inclination data indicating an inclination angle of a body of the work machine.

20. A work machine control system according to claim 17, wherein the controller changes the second speed threshold based on inclination data indicating an inclination angle of a body of the work machine.

21. A work machine control system according to claim 16, wherein the controller changes the first speed threshold based on detection data from a load sensor that detects the load state of a work implement provided on the work machine.

22. A work machine control system according to claim 21, wherein the load sensor includes a weight sensor that detects the weight of the work machine.

23. A work machine control system as set forth in claim 21, wherein the controller determines whether the work machine is in a loaded state or an unloaded state based on detection data from the load sensor, and sets a first speed threshold when the work machine is in the loaded state to be smaller than the first speed threshold when the work machine is in the unloaded state.

24. A work machine control system according to claim 17, wherein the controller changes the second speed threshold based on detection data from a load sensor that detects the load state of a work implement provided on the work machine.

25. A work machine control system as set forth in claim 24, wherein the controller determines whether the work machine is in a loaded state or an unloaded state based on detection data from the load sensor, and sets the second speed threshold when the work machine is in the loaded state to be smaller than the second speed threshold when the work machine is in the unloaded state.

26. A work machine comprising the work machine control system according to claim 14.

27. A remote operation system for a work machine, comprising: an operation device disposed outside the work machine; and the work machine control system according to claim 14.

28. A control method for a work machine, in which a controller executes the following steps: acquires an operation signal for switching the direction of travel of the work machine; determines whether the operation signal satisfies the acquired operating condition when the work machine is descending a slope with an inclination angle equal to or greater than an angle threshold; and prohibits output of a forward / reverse switch command for switching the direction of travel if it is determined that the operating condition is satisfied.

Images