Work machine, system including work machine, and method for controlling work machine

Abstract

The present invention makes it possible to avoid falling of loads from a work apparatus while a work machine is traveling. A work machine according to the present invention comprises: a vehicle body; a work apparatus that is attached to the vehicle body and has a bucket at the tip thereof; and a controller that commands the operations of the work apparatus. The controller operates the bucket to reduce the load mass in the bucket so that the load mass approaches a target load mass, which is a target value of the load mass. When the controller determines that the reduction of the load mass is completed, the controller operates the bucket in a tilt direction.

Description

Work machine, system including work machine, and method for controlling work machine

[0001] The present disclosure relates to a work machine, a system including a work machine, and a method for controlling a work machine.

[0002] U.S. Patent Application Publication No. 2017 / 0002542 (Patent Document 1) describes shaking the work tool to spill any loose material within the work tool onto the material pile, thereby preventing the loose material from spilling along a path from the material pile to a dump location.

[0003] US Patent Application Publication No. 2017 / 0002542

[0004] In order to maximize the amount of load that can be loaded from the work machine onto the transport machine, it is necessary to prevent the load from spilling from the work machine when the work machine travels toward the transport machine.

[0005] The present disclosure proposes a work machine, a system including the work machine, and a control method for the work machine that can prevent a load from spilling from the work machine when the work machine is traveling.

[0006] A work machine according to one aspect of the present disclosure includes a vehicle body, a work implement attached to the vehicle body and having a bucket at its tip, and a controller that commands operation of the work implement. The controller operates the bucket to reduce the load mass in the bucket so that the load mass approaches a target load mass, which is a target value for the load mass. When the controller determines that the load mass has been reduced, it operates the bucket in a tilt direction.

[0007] A system according to one aspect of the present disclosure includes a work machine. The work machine includes a vehicle body and a work implement attached to the vehicle body and having a bucket at its tip. The system also includes a controller that commands operation of the work implement. The controller operates the bucket to reduce the load mass in the bucket so that the load mass approaches a target load mass, which is a target value for the load mass. When the controller determines that the load mass has been reduced, it operates the bucket in a tilt direction.

[0008] A method for controlling a work machine according to one aspect of the present disclosure includes the following steps: a first step of operating the bucket at the tip of the work machine to reduce the mass of a load in the bucket so that the load mass approaches a target load mass, which is a target value; and a second step of operating the bucket in the tilt direction when it is determined that the load mass has been reduced.

[0009] According to the present disclosure, it is possible to prevent loads from spilling from the work machine when the work machine is traveling.

[0010] 1 is a side view of a wheel loader. FIG. 2 is a diagram for explaining dimensions of each part of the work machine and the balance of four moments. FIG. 3 is a schematic diagram for explaining tipping off after excavation work by the wheel loader. FIG. 4 is a functional block diagram showing the functional configuration of the wheel loader. FIG. 5 is a flow chart for explaining the processing flow of auto tipping off control. FIG. 6 is a flow chart showing the processing flow for calculating a target soil volume. FIG. 7 is a schematic diagram showing an overview of auto tipping off according to an embodiment. FIG. 8 is a schematic diagram showing the processing content in the control of Step 1. FIG. 9 is a schematic diagram showing the processing content in the control of Step 2. FIG. 10 is a graph showing the bucket speed in Step 2. FIG. 11 is a schematic diagram showing the processing content in the control of Step 3. FIG. 12 is a graph showing the rate of decrease in load mass in Step 3. FIG. 13 is a graph showing the bucket speed during auto tipping off execution. FIG. 14 is a flow chart for explaining the processing flow of full tilt control. FIG. 15 is a flow chart for explaining another example of the processing flow of auto tipping off control.

[0011] Hereinafter, the embodiments will be described with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated. In the drawings, configurations may be omitted or simplified for the sake of convenience. It is also intended from the beginning that any configurations may be extracted from the embodiments and arbitrarily combined.

[0012] <Configuration of Work Machine> As an example of a work machine according to the embodiment, the configuration of a wheel loader 1 will be described using Figure 1. The work machine in the embodiment is not limited to the wheel loader 1. The work machine may be any work machine equipped with a work implement having a bucket at the tip, and may be a backhoe, a loading shovel, or the like.

[0013] Figure 1 is a side view of a wheel loader 1 as an example of a work machine according to an embodiment. As shown in Figure 1, the wheel loader 1 has a body frame 2, a work implement 3, a traveling device 4, and a cab 5. The wheel loader 1 further has a controller 50 (Figure 4) that commands the operation of the work implement 3, which will be described later.

[0014] The vehicle frame 2 and cab 5 make up the vehicle body (machine body 9) of the wheel loader 1. Inside the cab 5, there are arranged a seat for the operator, operation devices, a monitor, etc. The operation devices include operation levers for traveling (forward and backward), operation levers for the work implement 3, input devices, etc. The work implement 3 and traveling device 4 are attached to the machine body 9 of the wheel loader 1. The work implement 3 is arranged in front of the machine body 9, and a counterweight 6 is provided at the rearmost end of the machine body 9.

[0015] The vehicle body frame 2 includes a front frame 11 and a rear frame 12. A steering cylinder 13 is attached to the front frame 11 and the rear frame 12. The steering cylinder 13 is a hydraulic cylinder. The steering cylinder 13 expands and contracts using hydraulic oil from a steering pump (not shown). The expansion and contraction of the steering cylinder 13 allows the front frame 11 and the rear frame 12 to swing left and right relative to each other. This allows the traveling direction of the wheel loader 1 to be changed left and right.

[0016] In this specification, the direction in which the wheel loader 1 travels straight ahead is referred to as the fore-and-aft direction of the wheel loader 1. In the fore-and-aft direction of the wheel loader 1, the side on which the work implement 3 is arranged relative to the body frame 2 is referred to as the front direction, and the side opposite the front direction is referred to as the rear direction. The left-and-right direction of the wheel loader 1 is the direction perpendicular to the fore-and-aft direction in a plan view. Looking forward, the right and left sides of the left-and-right direction are the right direction and the left direction, respectively. The up-and-down direction of the wheel loader 1 is the direction perpendicular to the plane defined by the fore-and-aft direction and the left-and-right direction. In the up-and-down direction, the side with the ground facing the ground is referred to as the bottom side, and the side with the sky facing the top side.

[0017] The traveling device 4 includes traveling wheels 4a, 4b. Each of the traveling wheels 4a, 4b is a wheel and has a tire made of rubber. The traveling wheel (front wheel) 4a is rotatably attached to the front frame 11. The traveling wheel (rear wheel) 4b is rotatably attached to the rear frame 12. The wheel loader 1 can be self-propelled by the traveling wheels 4a, 4b being rotationally driven.

[0018] The work implement 3 is used to perform work such as excavation, and is attached to a front frame 11. The work implement 3 includes a bucket 14, a boom 15, a bell crank 16, and a tilt rod 17.

[0019] The base end of the boom 15 is rotatably attached to the front frame 11 by a boom foot pin 21. This rotatably attaches the boom 15 to the machine body 9. The bucket 14 is rotatably attached to the tip of the boom 15 by a bucket pin 22. The bucket 14 is disposed at the tip of the work implement 3. The work implement 3 has the bucket 14 at its tip. The bucket 14 is a work tool used for excavation and loading. The cutting edge 14a is the tip of the bucket 14. The back surface 14b is part of the outer surface of the bucket 14 that extends rearward from the cutting edge 14a. The back surface 14b is formed as a flat surface.

[0020] The boom cylinder 18 drives the boom 15. One end of the boom cylinder 18 is rotatably attached to the front frame 11 of the machine body 9 by a pin 23. In this way, the boom cylinder 18 is rotatably attached to the machine body 9. The other end of the boom cylinder 18 is rotatably attached to the boom 15 by a pin 24.

[0021] The boom cylinder 18 is, for example, a hydraulic cylinder. The boom cylinder 18 extends and retracts using hydraulic fluid from a work equipment pump (not shown). This drives the boom 15, and the bucket 14 attached to the tip of the boom 15 moves up and down.

[0022] The boom cylinder 18 is attached to the machine body 9 through a tube 18a (cylinder tube) and to the boom 15. The boom cylinder 18 applies a thrust F of the boom cylinder 18 to the tube 18a. cyl The boom cylinder 18 has a rod 18b (piston rod) that is moved by hydraulic pressure (see FIG. 2). The rod 18b has a piston 18c. The piston 18c moves within the tube 18a due to hydraulic pressure, thereby changing the stroke length of the boom cylinder 18.

[0023] Bell crank 16 is rotatably supported on boom 15 by a support pin 29. Bell crank 16 has a first end located on one side of support pin 29 and a second end located on the opposite side of support pin 29 from the first end. The first end of bell crank 16 is connected to bucket 14 via tilt rod 17. The second end of bell crank 16 is connected to front frame 11 of machine body 9 via bucket cylinder 19.

[0024] One end of the tilt rod 17 is rotatably attached to a first end of the bell crank 16 by a pin 27. The other end of the tilt rod 17 is rotatably attached to the bucket 14 by a pin 28.

[0025] The bucket cylinder 19 drives the bucket 14 relative to the boom 15. The bucket cylinder 19 has one end and another end opposite the one end. One end of the bucket cylinder 19 is rotatably attached to the front frame 11 of the machine body 9 by a pin 25. The other end of the bucket cylinder 19 is rotatably attached to a second end of the bell crank 16 by a pin 26.

[0026] The bucket cylinder 19 is, for example, a hydraulic cylinder. The bucket cylinder 19 expands and contracts using hydraulic oil from a work equipment pump (not shown). This drives the bucket 14, which rotates up and down relative to the boom 15 around a bucket pin 22. The bucket cylinder 19 generates a driving force that moves the bucket 14 relative to the boom 15, with the tip of the boom 15 serving as a fulcrum. The direction in which the cutting edge 14a of the bucket 14 rises (moves upward) is called the tilt direction. The direction in which the cutting edge 14a of the bucket 14 lowers (moves downward) is called the dump direction.

[0027] The wheel loader 1 is driven by the thrust F of the boom cylinder 18. cyl and a sensor for detecting information relating to the thrust of the bucket cylinder 19. A thrust is defined as a force that pushes an object in the direction of movement, and the thrust F of the boom cylinder 18 is cyl is a thrust generated by the boom cylinder 18 that rotates the boom 15 relative to the vehicle body. The thrust of the bucket cylinder 19 is a thrust generated by the bucket cylinder 19 that rotates the bucket 14 relative to the boom 15.

[0028] The sensors that detect information related to the thrust of the boom cylinder 18 are, for example, pressure sensors 31b and 31h. Each of the pressure sensors 31b and 31h detects the cylinder pressure of the boom cylinder 18. The pressure sensor 31b detects the bottom pressure of the boom cylinder 18. The pressure sensor 31h detects the head pressure of the boom cylinder 18.

[0029] The head pressure means the pressure on the cylinder rod side relative to the piston of the hydraulic cylinder, and the bottom pressure means the pressure on the tube side relative to the piston.

[0030] The sensors that detect information related to the thrust of the bucket cylinder 19 are, for example, pressure sensors 32b and 32h. Each of the pressure sensors 32b and 32h detects the cylinder pressure of the bucket cylinder 19. The pressure sensor 32b detects the bottom pressure of the bucket cylinder 19. The pressure sensor 32h detects the head pressure of the bucket cylinder 19.

[0031] The wheel loader 1 further has a sensor that detects information relating to the attitude of the work implement 3. The sensor that detects information relating to the attitude of the work implement 3 includes, for example, a sensor that detects information relating to the boom angle and a sensor that detects information relating to the bucket ground angle θ Ｂ The information relating to the attitude of the work implement 3 will be described in detail later (FIG. 2).

[0032] The boom angle is the angle of the boom 15 relative to the front frame 11 of the machine body 9. More specifically, the boom angle is the angle formed between the boom 15 and an imaginary axis extending in the fore-and-aft direction of the vehicle body in a side view of the wheel loader 1 (FIG. 1) (more specifically, an axis that is horizontal when the ground G on which the wheel loader 1 travels is horizontal). The boom reference line P shown in FIG. 1 is a line that passes through the center of the boom foot pin 21 and the center of the bucket pin 22. The boom angle is the angle formed between the boom reference line P and a horizontal line extending forward from the center of the boom foot pin 21.

[0033] The sensor that detects information related to the boom angle is, for example, a potentiometer 33. The potentiometer 33 is attached so as to be concentric with the boom foot pin 21. Instead of the potentiometer 33, a stroke sensor 35 of the boom cylinder 18 may be used as the sensor that detects information related to the boom angle.

[0034] An IMU (Inertial Measurement Unit) 37 or an imaging device (e.g., a camera) 39 may be used as a sensor for detecting information related to the boom angle. The IMU 37 is attached to, for example, the boom 15. The imaging device 39 is attached to the machine body 9 (e.g., the cab 5).

[0035] The bell crank reference line Q shown in FIG. 1 is a line passing through the center of the support pin 29 and the center of the pin 26. The bell crank angle θ2 is the angle between the boom reference line P and the bell crank reference line Q. The bucket ground angle θ Ｂ is the angle of the bucket 14 with respect to the ground G. The bucket back surface extension line E shown in FIG. 1 is a straight line extending from the back surface 14b of the bucket 14 when viewed from the side. The bucket ground angle θ Ｂ is the angle between the ground G and the extension line E of the back surface of the bucket. By detecting the bell crank angle θ2, the bucket ground angle θ Ｂ When the back surface 14b of the bucket 14 is in a position parallel to the ground G, the bucket ground angle θ Ｂ When the bucket 14 is moved in the tilt direction, the bucket ground angle θ Ｂ When the bucket 14 is moved in the dump direction, the bucket ground angle θ Ｂ is taken as negative.

[0036] Bucket ground angle θ Ｂ The sensor that detects the information about the bucket angle θ is, for example, a potentiometer 34. The potentiometer 34 is attached so as to be concentric with the support pin 29. Ｂ As a sensor for detecting information relating to the above, a stroke sensor 36 of the bucket cylinder 19 may be used instead of the potentiometer 34 .

[0037] Bucket ground angle θ Ｂ The IMU 38 or the imaging device 39 may be used as a sensor for detecting information relating to the tilt rod 17. The IMU 38 is attached to the tilt rod 17, for example.

[0038] The potentiometers 33, 34, stroke sensors 35, 36, IMUs 37, 38, and imaging device 39 may be used as sensors that detect information related to the position of the center of gravity GC1 of the work implement 3. The potentiometers 33, 34, stroke sensors 35, 36, IMUs 37, 38, and imaging device 39 may be used as sensors that detect information related to the position of the center of gravity GC2 of the load in the bucket 14.

[0039] The wheel loader 1 may further include an angle sensor 40. The angle sensor 40 detects the tilt angle (pitch angle) of the machine body 9 with respect to a direction perpendicular to the direction of gravity, which serves as a reference (horizontal plane). For example, an IMU attached to the machine body 9 may be used as this angle sensor 40. The angle sensor 40 may be attached to any of the front frame 11, rear frame 12, and cab 5, as long as it is attached to the machine body 9.

[0040] <Calculation of Load Mass> FIG. 2 is a diagram for explaining the dimensions of each part of the work implement 3 and the balance of the four moments.

[0041] The above-mentioned "information relating to the attitude of the work implement 3" refers to the dimensions Rl2 and Rb5 shown in Fig. 2. The dimension Rl2 is the dimension between the boom foot pin 21 and the pin 23, and is the dimension in the direction perpendicular to the extension direction of the boom cylinder 18. The dimension Rb5 is the dimension between the boom foot pin 21 and the pin 26, and is the dimension in the direction perpendicular to the extension direction of the bucket cylinder 19.

[0042] The above-mentioned "information relating to the position of the center of gravity GC1 of the work implement 3" is the dimension RI3. The dimension RI3 is the dimension between the center of gravity GC1 and the boom foot pin 21, and is the dimension along the fore-and-aft direction of the wheel loader 1. When the ground G ( FIG. 1 ) on which the wheel loader 1 is placed is horizontal, the dimension RI3 is the dimension along the horizontal direction between the center of gravity GC1 and the boom foot pin 21.

[0043] The above-mentioned "information relating to the position of the center of gravity GC2 of the load in the bucket 14" is the dimension RI1. The dimension RI1 is the dimension between the center of gravity GC2 and the boom foot pin 21, and is the dimension along the fore-and-aft direction of the wheel loader 1. When the ground G on which the wheel loader 1 is placed is horizontal, the dimension RI1 is the dimension along the horizontal direction between the center of gravity GC2 and the boom foot pin 21.

[0044] The dimension Rb1 is the dimension between the center of gravity GC2 of the load and the pin 22, and is the dimension along the fore-and-aft direction of the wheel loader 1. When the ground G on which the wheel loader 1 is placed is horizontal, the dimension Rb1 is the dimension along the horizontal direction between the center of gravity GC2 of the load and the pin 22.

[0045] Dimension Rb2 is the dimension between pin 22 and pin 27, and is the dimension in the direction perpendicular to the extension direction of tilt rod 17. Dimension Rb3 is the dimension between pin 27 and support pin 29, and is the dimension in the direction perpendicular to the extension direction of tilt rod 17. Dimension Rb4 is the dimension between pin 26 and support pin 29, and is the dimension in the direction perpendicular to the extension direction of bucket cylinder 19.

[0046] The dimension Rb6 is the dimension between the center of gravity GC3 of the bucket 14 and the pin 22, and is the dimension along the front-to-rear direction of the wheel loader 1. When the ground G on which the wheel loader 1 is placed is horizontal, the dimension Rb6 is the dimension along the horizontal direction between the center of gravity GC3 of the bucket 14 and the pin 22.

[0047] The values ​​of Rli (i = 1 to 3) and Rbj (j = 1 to 6) are calculated by the controller 50 (Figure 4) based on the design dimensions of each member constituting the work implement 3, the boom angle, and the bell crank angle θ2.

[0048] In the following, the balance of the four moments will be used to calculate the load mass W, which is the mass of the excavation target scooped into the bucket 14 during the excavation work. load Referring to FIG. 2, the moment a due to the weight F1 of the cargo is calculated. Wload is expressed by the following equation (1).

[0049]

[0050] In equation (1), g is the acceleration due to gravity. The same applies to equations (2) and (4) described below.

[0051] Moment b due to the weight F2 of the work machine 3 Wload is calculated by multiplying the weight F2 of the work machine 3 by R13 (FIG. 2). Wload is expressed by the following equation (2).

[0052]

[0053] Mass W of the entire work machine 3 we is the sum of the masses of the bucket 14, boom 15, bell crank 16, and tilt rod 17 that constitute the work implement 3.

[0054] Thrust F of the boom cylinder 18 cyl Moment c due to Wload is expressed by the following equation (3).

[0055]

[0056] In equation (3), η is the hydraulic transmission efficiency of the boom 15. The moment d due to the reaction force F4 of the bucket 14 is Wload is expressed by the following equation (4).

[0057]

[0058] In formula (4), Wg bucket is the mass of the bucket 14. β is an empty load correction coefficient. β is a coefficient for correcting the empty load state when buckets 14 of different masses are attached to the boom 15.

[0059] Moment a due to the weight of the cargo F1 Wload and moment b due to the weight F2 of the work machine 3. Wload and the thrust F of the boom cylinder 18 cyl Moment c due to Wload and moment d due to reaction force F4 of the bucket 14. Wload A balance relation as shown in the following equation (5) holds between

[0060]

[0061] From equation (5), the cargo mass W load The following equation (6) is obtained: load is included in equations (1) and (4).

[0062]

[0063] <Excavation Work, Tipping-Off> The wheel loader 1 of this embodiment performs excavation work by excavating an excavation target such as earth and sand with the bucket 14 and scooping the excavation target into the bucket 14. After the excavation work, the wheel loader 1 calculates the load mass W load 3 is a schematic diagram illustrating tip-off after an excavation operation by the wheel loader 1 according to the embodiment.

[0064] As shown in Fig. 3(A), the wheel loader 1 moves forward toward the excavation target 100 and causes the cutting edge 14a of the bucket 14 to bite into the excavation target 100, and then raises the bucket 14 along the bucket trajectory L and moves the bucket 14 in the tilt direction, as shown by the arrow in Fig. 3(A). In this way, excavation work is performed in which the excavation target 100 is scooped into the bucket 14.

[0065] As shown in Figure 3(B), after the excavation target 100 has been scooped into the bucket 14, the wheel loader 1 moves backward in the load reverse process. As shown in Figure 3(C), the wheel loader 1 raises the boom 15 at a slow speed. As shown in Figure 3(D), the wheel loader 1 moves the bucket 14 in the dump direction while raising the boom 15. The wheel loader 1 drops a portion of the excavation target 100 in the bucket 14 from the bucket 14, reducing the load mass W load and the load mass W in the bucket 14 is reduced. load The tip-off is performed by bringing the load mass closer to the target value, which is the target load mass.

[0066] Load mass W in the bucket 14 load When tip-off is performed until the load mass W is close enough to the target load mass, load It is determined that the bucket 14 has finished decreasing, and as shown in Figure 3(E), the bucket 14 moves in the tilt direction. The bucket 14 moves to a full tilt state. A full tilt state means a state in which the front end of the bucket 14 is raised until the bucket 14 stops at the tilt-side stopper. When the bucket 14 is in a full tilt state, the bucket cylinder 19 is at the stroke end on the extension side. When the bucket 14 is in a full tilt state, the bucket ground angle θＢ takes the maximum positive value.

[0067] Thereafter, the wheel loader 1 performs a loading operation in which the excavation target 100 in the bucket 14 is loaded onto a transport machine such as a dump truck.

[0068] <Functional Configuration> Next, a description will be given of the functional configuration of the wheel loader 1. In particular, the functional blocks of the controller 50 that automatically executes tipping off (auto-tip off) after excavation work in the wheel loader 1 shown in Fig. 1 will be described using Fig. 4.

[0069] Figure 4 is a functional block diagram showing the functional configuration of the wheel loader 1. As shown in Figure 4, the wheel loader 1 comprises a controller 50, an input unit 51, and a display unit 52. The input unit 51 includes an input device such as an operation panel. The operation panel may be configured to include hard keys and / or software keys. The input unit 51 includes an operation lever for the work implement 3. The display unit 52 corresponds to a monitor. The input unit 51 and the display unit 52 are installed inside the cab 5. The display unit 52 may be a touch panel. The display unit 52 may have some of the functions of the input unit 51.

[0070] The controller 50 includes a memory unit 500, a boom cylinder thrust calculation unit 501, a hydraulic transmission efficiency calculation unit 502, a dimension value calculation unit 503, a bucket ground angle calculation unit 505, a target cargo mass calculation unit 508, a cargo mass calculation unit 509, and an automatic tip-off control unit 510. The automatic tip-off control unit 510 includes an auto-tip-off start determination unit 511, an auto-tip-off control unit 512, and an auto-tip-off end determination unit 513.

[0071] The storage unit 500 stores in advance various data input via the input unit 51. The storage unit 500 stores the mass Wg of the bucket 14, bucket and the mass W of the entire work machine 3 we , the empty load correction coefficient β, the work implement design dimension values, the work implement design center of gravity position, and the capacity of the bucket 14 are stored.

[0072] The work machine design dimension values ​​are the design dimension values ​​of each component that constitutes the work machine 3, such as the bucket 14, boom 15, bell crank 16, tilt rod 17, etc. For the boom 15, for example, the work machine design dimension values ​​are the distance between the through hole into which the boom foot pin 21 is inserted and the through hole into which the bucket pin 22 is inserted, the distance between the through hole into which the boom foot pin 21 is inserted and the through hole into which the pin 24 is inserted, etc.

[0073] The work implement design center of gravity position is the theoretical value of the position of the center of gravity GC1 of the work implement 3. The work implement design center of gravity position is the center of gravity position in a coordinate system specific to the work implement 3. The work implement design center of gravity position is indicated as a coordinate value when a specific position of the work implement 3 is set as the origin for the work implement 3. The position of the origin can be set so that the work implement design center of gravity position can be expressed in a two-dimensional coordinate system. For example, the center of the through hole into which the boom foot pin 21 is inserted in a side view of the boom 15 can be set as the specific position (origin).

[0074] The work implement design dimension values ​​are used in the dimension value calculation unit 503. The work implement design center of gravity position and the mass Wg of the bucket 14 bucket and the mass W of the entire work machine 3 we and the empty load correction coefficient β are used in the cargo mass calculation unit 509.

[0075] The boom cylinder thrust calculation unit 501 calculates the thrust F of the boom cylinder 18 described above based on the cylinder pressure detected by the pressure sensors 31b and 31h. cyl Specifically, the boom cylinder thrust calculation unit 501 calculates the thrust F based on the bottom pressure of the boom cylinder 18 acquired from the pressure sensor 31b and the head pressure acquired from the pressure sensor 31h. cyl The boom cylinder thrust calculation unit 501 periodically calculates the thrust F from only the bottom pressure of the boom cylinder 18 that has been acquired. cyl The calculated thrust F cyl The value of is sent to the cargo mass calculation unit 509.

[0076] The hydraulic transmission efficiency calculation unit 502 calculates the hydraulic transmission efficiency η of the boom 15 based on the value of the boom angle detected by the sensor that detects information related to the boom angle described above. More specifically, the hydraulic transmission efficiency calculation unit 502 calculates the amount of change per unit time in the value of the boom angle, and determines the hydraulic transmission efficiency η based on this amount of change. The hydraulic transmission efficiency calculation unit 502 sends the calculated hydraulic transmission efficiency η to the load mass calculation unit 509. The calculated hydraulic transmission efficiency η is substituted into the above-described equation (3).

[0077] As described above, instead of calculating the hydraulic transmission efficiency η each time, a predetermined constant value may be used as the hydraulic transmission efficiency η.

[0078] The dimension value calculation unit 503 calculates the values ​​of the above-mentioned dimensions Rli (i = 1 to 3) and Rbj (j = 1 to 6) using the work machine design dimension values, boom angle, and bell crank angle θ2 stored in the memory unit 500. The dimension value calculation unit 503 periodically calculates the values ​​of the dimensions Rli (i = 1 to 3) and Rbj (j = 1 to 6). The dimension value calculation unit 503 sends the calculation results to the load mass calculation unit 509.

[0079] The bucket ground angle calculation unit 505 calculates the bucket ground angle θ 2 described above using the work machine design dimension values, the boom angle, and the bell crank angle θ 2 stored in the storage unit 500. Ｂ The bucket ground angle calculation unit 505 sends the calculation result to the auto tip-off control unit 512.

[0080] The target load mass calculation unit 508 calculates the target soil volume, which is the target value for the mass of the load to be loaded in the bucket 14 at the end of tip-off, based on the maximum load capacity of the transport machine input via the input unit 51 and the capacity of the bucket 14. The target soil volume corresponds to an example of a "target load mass," which is the target value for the load mass for auto tip-off. The target load mass calculation unit 508 sends the calculation result to the auto tip-off start determination unit 511, the auto tip-off control unit 512, and the auto tip-off end determination unit 513.

[0081] The cargo mass calculation unit 509 calculates each mass Wg bucket , W we , the correction coefficient β, and the thrust Fcyl The cargo mass calculation unit 509 periodically calculates the cargo mass using the above-mentioned formulas (1) to (6) based on the hydraulic transmission efficiency η, the dimensions Rli (i = 1 to 3), and Rbj (j = 1 to 6). The cargo mass calculation unit 509 periodically sends the calculated cargo mass value to the auto tip-off start determination unit 511, the auto tip-off control unit 512, and the auto tip-off end determination unit 513.

[0082] The auto tip-off start determination unit 511, auto tip-off control unit 512, and auto tip-off end determination unit 513 perform auto tip-off control based on operation information of the operating lever for the work implement 3 input via the input unit 51, the calculated target soil volume, and the load mass. The auto tip-off control unit 512 outputs control signals indicating flow rate commands to the boom cylinder 18 and the bucket cylinder 19. The automatic tip-off control unit 510 displays information on the display unit 52.

[0083] <Control Structure> FIG. 5 is a flowchart for explaining the flow of the auto tip-off control process executed by the controller 50. As shown in FIG.

[0084] In step S1, the excavation work ends. The excavation work may be performed automatically, or the operator may perform the excavation work manually. The controller 50 recognizes that excavation has ended. The controller 50 determines that the excavation operation of the wheel loader 1 has ended based on the operation details of the operating lever for travel (forward / backward movement) and the operating lever for the work implement 3, information about the attitude of the work implement 3, information about the thrust of the boom cylinder 18, information about the thrust of the bucket cylinder 19, and the like.

[0085] In step S2, the wheel loader 1 moves backward with the load. The operator may manually move the wheel loader 1 backward. The controller 50 may also automatically move the wheel loader 1 backward with the load. The controller 50 may send a control signal to the traveling device 4 to move the wheel loader 1 backward, while maintaining the attitude of the work implement 3 and keeping the load loaded in the bucket 14.

[0086] In step S3, the operator operates the tip-off start button. The controller 50 (auto-tip-off start determination unit 511 of the automatic tip-off control unit 510) receives input that the tip-off start button has been pressed. The tip-off start button is a button that is operated by the operator to start auto-tip-off. The input unit 51 includes the tip-off start button. By including the pressing of the tip-off start button as a condition for starting auto-tip-off, it becomes possible to perform tip-off automatically in accordance with the will of the operator who wishes to perform auto-tip-off.

[0087] A physical push button switch may be arranged in the cab 5 as the tip-off start button, and the push button switch may be electrically connected to the controller 50 so that an operator can input an operation of pressing the push button switch into the controller 50. Alternatively, the controller 50 may display the tip-off start button on the display unit 52, which is a touch panel.

[0088] In step S4, the controller 50 (auto tip-off start determination unit 511) recognizes that the dump operation of the bucket 14 has continued for one second. A dump operation refers to the operation of the control lever for the work implement 3 in a direction that moves the bucket 14 in the dump direction. The controller 50 receives input of the operation content of the control lever from the control lever for the work implement 3. The controller 50 determines that the control lever for the work implement 3 has been operated to dump, and that the dump operation has continued for one second.

[0089] When the tip-off start button is pressed in step S3 and the dump operation of the bucket 14 continues for one second in step S4, the controller 50 (auto-tip-off control unit 512 of the automatic tip-off control unit 510) raises the boom 15 in step S5. The controller 50 outputs a control signal to extend the boom cylinder 18. Hydraulic oil flows into the oil chamber on the bottom side of the boom cylinder 18, and the piston 18c moves toward the tip of the tube 18a, thereby extending the boom cylinder 18. As the boom cylinder 18 extends, the boom 15 rises.

[0090] In step S6, the controller 50 (auto tip-off control unit 512) determines whether the post-excavation soil volume, which is the load mass in the bucket 14 after the excavation work, is greater than the target soil volume (target load mass), which is the target value for the load mass in the bucket 14.

[0091] 6 is a flow chart showing the flow of a process for calculating the target soil volume. The controller 50 automatically calculates the target value of the load mass in excavation work from the maximum load capacity of the dump truck and the capacity of the bucket 14.

[0092] In step S101, a loading operation is started in which the cargo in the bucket 14 is loaded onto a dump truck, which is an example of a conveyance machine. The wheel loader 1 is caused to travel forward toward the dump truck, and the bucket 14 is moved onto the bed of the dump truck, and the bucket 14 is then moved in the dumping direction, thereby loading the cargo in the bucket 14 onto the bed of the dump truck. The loading operation may be performed manually by an operator, or may be performed automatically by the controller 50.

[0093] In step S102, the controller 50 acquires the maximum load capacity of the bed of the dump truck that is the target of the loading operation. The operator inputs the maximum load capacity of the dump truck by operating the input unit 51. In response to the operator's input, the controller 50 acquires the maximum load capacity of the dump truck.

[0094] In step S103, the controller 50 determines whether the auto tip-off mode is ON. Based on the operator's operation, it is set whether auto tip-off is executed after the excavation work (auto tip-off mode ON), or whether tip-off is performed manually after the excavation work and auto tip-off is not executed (auto tip-off mode OFF). The operator may set the auto tip-off mode by operating the input unit 51. The setting of the auto tip-off mode may be displayed on the display unit 52.

[0095] If it is determined that the auto tip-off mode is ON (YES in step S103), in step S104, the controller 50 determines whether the remaining amount of cargo that can be loaded onto the bed of the dump truck is smaller than the capacity of the bucket 14. The controller 50 acquires the amount of cargo loaded on the dump truck at the time the loading operation in step S101 is completed and the maximum load capacity of the dump truck.

[0096] The controller 50 calculates the remaining load capacity by subtracting the amount of cargo already loaded on the dump truck from the maximum load capacity of the dump truck. The controller 50 compares the capacity of the bucket 14 stored in the memory unit 500 with the calculated remaining load capacity to determine whether the remaining load capacity is smaller than the capacity of the bucket 14.

[0097] If it is determined that the remaining load capacity is smaller than the capacity of the bucket 14 (YES in step S104), in step S105, the controller 50 sets the weight obtained by adding the margin value N to the remaining load capacity calculated in step S104 as the target soil volume (target load mass), which is the target value for the load mass in the bucket 14 during auto tip-off. The controller 50 sets a larger load mass for tip-off. By loading a larger load into the bucket 14 during excavation work and then discharging the excess load from the bucket 14 during tip-off, the accuracy of the load mass in the bucket 14 at the end of tip-off can be improved.

[0098] If it is determined in step S103 that the auto tip-off mode is OFF (NO in step S103), or if it is determined in step S104 that the capacity of the bucket 14 is equal to or greater than the remaining load capacity (NO in step S104), then in step S106, controller 50 performs a calculation to divide the maximum load capacity of the dump truck by the capacity of the bucket 14. From the result of this calculation, controller 50 calculates an equally distributed excavation amount by equally dividing the maximum load capacity of the dump truck.

[0099] In step S107, the operator inputs a command to start automatic excavation by operating the automatic excavation enable button on the input unit 51. The automatic excavation enable button may be a physical push button switch, or may be displayed on the display unit 52, which is a touch panel. In response to this input, the controller 50 starts automatic excavation of the excavation target by the wheel loader 1. In this way, a series of processes for calculating the target soil volume is carried out.

[0100] Returning to Figure 5, when the determination in step S6 is that the target soil volume is smaller than the post-excavation soil volume, i.e., when the load mass, which is the mass of the excavation target in the bucket 14 after excavation work, is greater than the target value for the load mass in the bucket 14 (target load mass) (YES in step S6), the controller 50 (auto-tip-off control unit 512) starts auto-tip-off in step S7. The controller 50 starts driving the bucket cylinder 19, which moves the bucket 14 in the dumping direction. The operation of raising the boom 15, which was started in step S5, continues during auto-tip-off.

[0101] 7 is a schematic diagram showing an overview of auto tip-off according to an embodiment. In the auto tip-off according to the embodiment, of the three steps of Step 1, Step 2, and Step 3, the processing of Step 1 is executed first, and then either or both of the processing of Step 2 and Step 3 are executed.

[0102] As shown in Figure 7, in the processing of Step 1, control is executed to dump soil roughly in accordance with the target soil volume. In the processing of Step 2, the speed of the bucket 14 is determined based on the instantaneous load, which is the current load mass in the bucket 14, and the target soil volume, which is the target value for the load mass. Specifically, control is executed to move the bucket 14 in the dumping direction at a speed determined by the magnitude of the difference between the instantaneous load and the target soil volume. In the processing of Step 3, control is executed to move the bucket 14 so that the rate at which the instantaneous load, which is the current load mass in the bucket 14, decreases is constant.

[0103] In step S8, the controller 50 (auto tip-off control unit 512) performs control of Step 1. Fig. 8 is a schematic diagram showing the processing content in the control of Step 1.

[0104] As shown in FIG. 8, in the control of Step 1, the load mass and the attitude of the bucket 14 (specifically, the bucket ground angle θ Ｂ ) and the target bucket ground angle θ Ｔ The table T1 shown in FIG. 8 shows an example of the relationship between the load mass and the attitude of the bucket 14. The table T1 is stored in the storage unit 500. For example, the table T1 is used to calculate the relationship between the load mass in the bucket 14 and the attitude of the bucket 14 (bucket ground angle θ) when the load is discharged from the bucket 14 after the load mass in the bucket 14 is maximized. Ｂ ) and can be created by obtaining the

[0105] In the table T1, the horizontal axis represents the soil volume (unit: ton), and the vertical axis represents the bucket ground angle θ Ｂ (unit: deg) As described above, the bucket ground angle θ Ｂ When the bucket angle θ is 0°, the back surface 14b of the bucket 14 is parallel to the ground G. Ｂ is a positive value, the back surface 14b of the bucket 14 is inclined with respect to the ground G so that the closer it is to the cutting edge 14a, the higher it is positioned. Ｂ When the value of is negative, the back surface 14b of the bucket 14 is inclined with respect to the ground surface G so that the back surface 14b is positioned lower as it approaches the cutting edge 14a.

[0106] The curve shown by the solid line in the table T1 represents the bucket ground angle θ Ｂ The curve is a smoothed result of determining the amount of soil in the bucket 14 when each value of is taken. The curve shown by the dashed line in table T1 is a curve obtained by moving the solid curve parallel to the top. The dashed curve indicates the attitude of the bucket 14 in the tilt direction, with a margin taken for the attitude of the bucket 14 when a specific amount of cargo is stored in the bucket 14.

[0107] In the auto tip-off mode, the controller 50 performs a dump operation on the bucket 14. The load in the bucket 14 is dropped from the cutting edge 14a side, reducing the load mass in the bucket 14 and bringing the load mass closer to the calculated target soil volume. The controller 50 determines a specific bucket attitude (target bucket ground angle θ) based on the calculated target soil volume and the dashed line shown in table T1. Ｔ The controller 50 determines the target bucket ground angle θ using the dashed line instead of the solid line shown in table T1. Ｔ The following is established.

[0108] The controller 50 determines the bucket ground angle θ when the target soil volume is accommodated in the bucket 14. Ｂ Bucket ground angle θ Ｂ The target bucket ground angle θ Ｔ The controller 50 determines the bucket ground angle θ when the target soil volume is accommodated in the bucket 14. Ｂ The bucket ground angle θ is greater than Ｂ The target bucket ground angle θ Ｔ The controller 50 determines the bucket ground angle θ when the bucket 14 is in a tilted position relative to the position of the bucket 14 when the target soil volume is accommodated in the bucket 14. Ｂ The target bucket ground angle θ Ｔ The controller 50 determines the bucket ground angle θ when the bucket 14 is tilted back from the attitude when the target soil volume is accommodated in the bucket 14. Ｂ The target bucket ground angle θ Ｔ Here, the tilted back posture is defined as the posture where the bucket ground angle θ Ｂ This means that the posture has a large value.

[0109] The controller 50 operates the bucket 14 in the dump direction toward a specific bucket attitude, and discharges the excavated object in the bucket 14 from the bucket 14. In this way, the controller 50 reduces the load mass in the bucket 14. The controller 50 operates the bucket 14 in the dump direction, and controls the bucket ground angle θＢ The bucket's ground angle θ is aimed at Ｔ Get closer to.

[0110] In Step 1, the controller 50 moves the bucket 14 in the dump direction at a constant speed. The controller 50 determines the speed of the bucket 14 toward a specific bucket attitude based on the target soil volume (target load mass). In table T2 shown in FIG. 8 , the horizontal axis represents the target soil volume (unit: ton) and the vertical axis represents the target bucket flow rate (unit: %). The target bucket flow rate is the flow rate of hydraulic oil supplied to the bucket cylinder 19. Table T2 is stored in the memory unit 500.

[0111] To move the bucket 14 in the tilt direction, the length of the bucket cylinder 19 is increased. Hydraulic oil flows into the oil chamber on the bottom side of the bucket cylinder 19. At this time, the target bucket flow rate is assumed to be a positive value. To move the bucket 14 in the dump direction, the length of the bucket cylinder 19 is decreased. Hydraulic oil flows into the oil chamber on the head side of the bucket cylinder 19. At this time, the target bucket flow rate is assumed to be a negative value.

[0112] Table T2 shows an example of a target bucket flow rate in the control of Step 1 of auto-tip-off. When auto-tip-off is performed, the bucket 14 moves in the dump direction. Therefore, the vertical axis of Table T2 takes on a range of negative values. When the target bucket flow rate is 0%, the amount of hydraulic oil flowing into the head-side oil chamber of the bucket cylinder 19 is zero. When the target bucket flow rate is minus 100%, the amount of hydraulic oil flowing into the head-side oil chamber of the bucket cylinder 19 is at its maximum. The closer the target bucket flow rate is to 0%, the slower the speed of the bucket 14. The closer the target bucket flow rate is to minus 100%, the faster the speed of the bucket 14 moving in the dump direction.

[0113] As shown in table T2, the controller 50 increases the speed of the bucket 14 moving in the dump direction as the target soil volume decreases. When the target soil volume is small, it is necessary to discharge a large amount of the load loaded in the bucket 14, and the target bucket ground angle θ Ｔbecomes a small value. Therefore, the speed of the bucket 14 is increased to discharge the load from the bucket 14 in a shorter time, so that the load mass can be reduced in a short time. On the other hand, if the target soil volume is large, the amount of load discharged from the bucket 14 may be small, so the speed of the bucket 14 is reduced to prevent excessive discharge of the load.

[0114] The target bucket flow rate determined by the target soil volume (target load mass) is converted into a flow rate / voltage to determine the bucket lever voltage. This flow rate / voltage conversion may be performed by the controller 50 or by a vehicle controller mounted on the wheel loader 1. The bucket cylinder 19 is controlled using this determined bucket lever voltage as the control variable for Step 1. In this way, the operation of moving the bucket 14 in the dump direction to reduce the load mass in the bucket 14 is performed automatically.

[0115] Returning to FIG. 5, in step S9, the controller 50 (auto tip-off control unit 512) calculates the current bucket ground angle θ Ｂ and the target bucket ground angle θ Ｔ The current bucket ground angle θ Ｂ The target bucket angle θ Ｔ If so (NO in step S9), the process returns to step S8, and the controller 50 continues the control of step S1.

[0116] Current bucket ground angle θ Ｂ The target bucket angle θ Ｔ (YES in the determination of step S9), the controller 50 ends the control of step 1 and proceeds to the control of step 2 or step 3. Ｂ Based on this, the control of Step 1 is switched to the control of Step 2 or Step 3.

[0117] In step S10, the controller 50 (auto tip-off control unit 512) performs control of Step 2. Fig. 9 is a schematic diagram showing the processing content in the control of Step 2.

[0118] As shown in Figure 9, in the control of Step 2, the controller 50 performs a calculation to determine the difference between the current cargo mass and the target soil volume. The controller 50 determines the difference obtained by subtracting the target soil volume from the current cargo mass as the current cargo mass difference u. The controller 50 calculates the square of the absolute value of the current cargo mass difference u and multiplies it by a proportionality coefficient k2 to convert the cargo mass difference u to a target bucket flow rate. The cargo mass difference u is squared in order to emphasize the difference in cargo mass.

[0119] The square of the absolute value of the load mass difference u is a positive value, and the proportionality coefficient k2 is a negative value, so the target bucket flow rate is a negative value. The target bucket flow rate is a value that determines the speed of the bucket 14 moving in the dumping direction. The target bucket flow rate is converted into a flow rate / voltage to determine the bucket lever voltage. The bucket cylinder 19 is controlled using this determined bucket lever voltage as the control amount in Step 2.

[0120] Figure 10 is a graph showing the speed of the bucket 14 in Step 2. The horizontal axis of the graph shown in Figure 10 represents the current load mass difference u, and the vertical axis represents the speed of the bucket 14 moving in the dump direction. The speed of the bucket 14 in Step 2 is determined by the current load mass and the target load mass (target soil volume). More specifically, the speed of the bucket 14 in Step 2 is determined by the magnitude of the difference between the current load mass and the target load mass.

[0121] As shown in Figure 10, when the current load mass difference u is large, the dumping speed of the bucket 14 is high, and when the current load mass difference u is small, the dumping speed of the bucket 14 is low. The larger the current load mass, the larger the load mass difference u, and the higher the dumping speed of the bucket 14. During the processing of Step 2, the load is discharged from the bucket 14, reducing the load mass and gradually reducing the load mass difference u. As time passes after the control of Step 2 is started, the dumping speed of the bucket 14 gradually decreases.

[0122] Returning to FIG. 5 , in step S11, the controller 50 (auto tip-off control unit 512) compares the current load mass with a predetermined threshold determined by the target soil volume. In this embodiment, the threshold is the target soil volume plus mass α. Mass α is set in advance and stored in the memory unit 500. Mass α is set to a relatively small value. Mass α may be a value less than 0.5 ton, for example. The controller 50 compares the current load mass with (target soil volume + α). The controller 50 determines whether the current load mass is smaller than (target soil volume + α). By setting the target soil volume plus mass α as the threshold, the load in the bucket 14 is prevented from being reduced too much during tip-off.

[0123] If the current cargo mass is equal to or greater than the threshold value (NO in step S11), the process proceeds to step S12. In step S12, the controller 50 (auto tip-off control unit 512) calculates the current bucket ground angle θ Ｂ It is determined whether the bucket ground angle θ is smaller than 0°. Ｂ The attitude of the bucket 14 when the angle θ is 0° corresponds to an example of the "second specific bucket attitude." Ｂ is the bucket ground angle θ when the bucket 14 assumes a specific bucket posture. Ｂ (Aiming bucket ground angle θ Ｔ 8). The bucket ground angle θ when the bucket 14 assumes the second specific bucket position is different from the bucket ground angle θ when the bucket 14 assumes the second specific bucket position. Ｂ is not limited to 0° and may be other angles.

[0124] In the control of Step 2, the bucket 14 moves in the dump direction and approaches a second specific bucket attitude. Ｂ If the current bucket ground angle θ is equal to or greater than 0° (NO in step S12), the process returns to step S10, and the controller 50 continues the control in step 2. ＢIf the bucket ground angle θ is smaller than 0° (YES in the determination of step S12), the controller 50 ends the control of step 2 and proceeds to the control of step 3. Ｂ Based on this, the control is switched from Step 2 to Step 3.

[0125] In step S13, the controller 50 (auto tip-off control unit 512) performs control of Step 3. Fig. 11 is a schematic diagram showing the processing content in the control of Step 3.

[0126] 11 , in the control of Step 3, the controller 50 performs a calculation to determine the difference between the current cargo mass and the previously calculated cargo mass. The controller 50 calculates the difference by subtracting the immediately previous cargo mass from the current cargo mass. The controller 50 then divides the calculated difference by the elapsed time from when the immediately previous cargo mass was acquired to the present, thereby calculating the current rate of decrease of the cargo mass.

[0127] The controller 50 further performs a calculation to determine the difference between the current cargo mass reduction rate and the target cargo mass reduction rate. The target cargo mass reduction rate is set in advance. The controller 50 calculates the difference by subtracting the target cargo mass reduction rate from the current cargo mass reduction rate, and sets the calculated difference as the current speed difference. The controller 50 multiplies the current speed difference by a proportionality coefficient k3 to convert the speed difference into a bucket flow rate. The proportionality coefficient k3 is a positive value.

[0128] A positive current speed difference indicates that the current load mass reduction rate is greater than the target load mass reduction rate, and that the speed at which the load in the bucket 14 is being discharged from the bucket 14 is too high. A negative current speed difference indicates that the current load mass reduction rate is less than the target load mass reduction rate, and that the speed at which the load in the bucket 14 is being discharged from the bucket 14 is too low, or that the load in the bucket 14 has not been discharged from the bucket 14.

[0129] The controller 50 calculates the target bucket flow rate by adding the bucket flow rate determined from the current speed difference to the previously determined target bucket flow rate. Because the bucket 14 is performing a dump operation, the previous target bucket flow rate is a negative value. If the current speed difference is positive, the target bucket flow rate calculated by this calculation will be a negative value with a smaller absolute value than the previous target bucket flow rate. The speed at which the bucket 14 is moved in the dump direction decreases. If the current speed difference is negative, the target bucket flow rate calculated by this calculation will be a negative value with a larger absolute value than the previous target bucket flow rate. The speed at which the bucket 14 is moved in the dump direction increases.

[0130] The target bucket flow rate is converted into a flow rate / voltage to obtain a bucket lever voltage. The obtained bucket lever voltage is used as a control variable in Step 3 to control the bucket cylinder 19.

[0131] Figure 12 is a graph showing the rate of decrease in cargo mass in Step 3. The horizontal axis of the graph shown in Figure 12 represents the elapsed time since control in Step 3 was initiated. The vertical axis of the graph represents cargo mass. In Step 3, the controller 50 operates the bucket 14 so that the rate of decrease in cargo mass becomes constant. The graph shown in Figure 12 is linear, with a constant slope. The amount of decrease in cargo mass per unit time becomes constant after control in Step 3 is initiated.

[0132] Figure 13 is a graph showing the speed of the bucket 14 during execution of auto tip-off. The horizontal axis of the graph shown in Figure 13 represents the elapsed time since the start of auto tip-off. The vertical axis of the graph represents the speed of the bucket 14 moving in the dump direction. Figure 13 shows an example in which Step 1 control is performed from time 0 to time T12, Step 2 control is performed from time T12 to time T23, and Step 3 control is performed from time T23 onwards.

[0133] In the control of Step 1, the controller 50 moves the bucket 14 in the dumping direction at a constant speed. As time passes after the control of Step 2 is started, the dumping speed of the bucket 14 gradually decreases. When the control shifts to Step 3, the dumping speed of the bucket 14 further decreases. The controller 50 makes the speed of the bucket 14 in Step 2 slower than the speed of the bucket 14 in Step 1. The controller 50 makes the speed of the bucket 14 in Step 3 slower than the minimum speed of the bucket 14 in Step 2. The controller 50 makes the speed of the bucket 14 in Step 3 slower than the speed of the bucket 14 in Step 1.

[0134] 5, in step S14, the controller 50 (auto tip-off termination determination unit 513) determines whether the current load mass is less than the target soil mass + α. The determination in step S14 is performed in the same manner as in step S11. If the current load mass is equal to or greater than the threshold value (NO in step S14), the process returns to step S13, and the controller 50 continues the control in step 3.

[0135] If the determination in step S11 or step S14 indicates that the current cargo mass is smaller than the threshold value (YES in step S11 or YES in step S14), controller 50 determines that the cargo mass in bucket 14 has been reduced. Controller 50 ends control of moving bucket 14 in the dump direction. In step S15, controller 50 performs full tilt control, moving bucket 14 in the tilt direction up to the full tilt state. Figure 14 is a flow chart for explaining the flow of processing for full tilt control.

[0136] In step S151, the controller 50 ends tip-off by stopping the movement of the bucket 14 in the dump direction so that the load mass in the bucket 14 does not decrease any further.

[0137] In step S152, the controller 50 holds the boom angle at the end of tip-off. The operation of raising the boom 15, which was started in step S5 shown in Fig. 5, is maintained while the bucket 14 is operated by the control of steps 1, 2, and 3, and continues up to step S152. In step S152, the controller 50 stops the operation of raising the boom 15. Thereafter, the controller 50 does not operate the boom 15. The controller 50 holds the boom angle when the boom 15 was stopped.

[0138] In step S153, controller 50 determines target bell crank angle c. Target bell crank angle c is the bell crank angle θ2 when the bucket 14 is in a fully tilted state. Target bell crank angle c changes depending on the boom angle. A table or graph showing the relationship between the boom angle and target bell crank angle c is stored in memory unit 500. Controller 50 determines target bell crank angle c by applying the boom angle when boom 15 was stopped in the previous step S152 to the relationship between the boom angle and target bell crank angle c.

[0139] In step S154, the controller 50 sets a bucket tilt flow rate. The bucket tilt flow rate is the flow rate of hydraulic oil supplied to the bucket cylinder 19 to move the bucket 14 in the tilt direction. The bucket tilt flow rate is set in the range from 0% to 100%, and the larger the bucket tilt flow rate, the faster the speed of the bucket 14 moving in the tilt direction. In step S154, the controller 50 sets a set value for the bucket tilt flow rate to FR1. The set value FR1 is set to a relatively large value. The set value FR1 is set to a value close to 100%. The set value FR1 may be, for example, a value of 80% or more.

[0140] The controller 50 supplies hydraulic oil to the oil chamber on the bottom side of the bucket cylinder 19 at the bucket tilt flow rate set value FR1, thereby increasing the length of the bucket cylinder 19. This increases the bell crank angle θ2, and the bucket 14 moves in the tilt direction. The bucket 14 moves in the tilt direction at high speed.

[0141] In step S155, controller 50 compares the current bell crank angle θ2 with the angle obtained by subtracting angle β from target bell crank angle c. Angle β is set in advance and stored in memory unit 500. Angle β is set to a relatively small angle. For example, angle β may be an angle less than 10°. Controller 50 compares the current bell crank angle θ2 with angle (c-β). Controller 50 determines whether or not the current bell crank angle θ2 is greater than angle (c-β). The attitude of the bucket 14 when bell crank angle θ2 is angle (c-β) corresponds to an example of a "predetermined bucket attitude."

[0142] If the current bell crank angle θ2 is equal to or less than the angle (c−β) (NO in the determination in step S155), the process returns to step S154, and the process of moving the bucket 14 in the tilt direction in step S154 and the determination in step S155 are repeated.

[0143] If it is determined that the current bell crank angle θ2 has become larger than the angle (c−β) due to continued movement of the bucket 14 in the tilt direction (YES in step S155), then in step S156 the controller 50 changes the set value of the bucket tilt flow rate. In step S156, the controller 50 sets the set value of the bucket tilt flow rate to a value different from FR1. The controller 50 sets the set value of the bucket tilt flow rate to FR2, which is smaller than FR1. The set value FR2 is set to a relatively small value. The set value FR2 is set to a value close to 0%. The set value FR2 may be, for example, a value equal to or less than 15%.

[0144] The controller 50 supplies hydraulic oil to the oil chamber on the bottom side of the bucket cylinder 19 so that the bucket tilt flow rate becomes the set value FR2. The length of the bucket cylinder 19 increases, the bell crank angle θ2 increases, and the bucket 14 moves in the tilt direction. By decreasing the set value of the bucket tilt flow rate, the rate at which the length of the bucket cylinder 19 increases decreases. The speed of the bucket 14 moving in the tilt direction decreases. The bucket 14 moves in the tilt direction at a low speed toward a fully tilted attitude. The controller 50 makes the speed of the bucket 14 after the bell crank angle θ2 becomes greater than the angle (c-β) slower than the speed of the bucket 14 when the bell crank angle θ2 is equal to or less than the angle (c-β).

[0145] In step S157, the controller 50 compares the current bell crank angle θ2 with the target bell crank angle c. The controller 50 determines whether the current bell crank angle θ2 is greater than the target bell crank angle c.

[0146] If the current bell crank angle θ2 is equal to or less than the target bell crank angle c (NO in step S157), the process returns to step S156, and the process of moving the bucket 14 in the tilt direction in step S156 and the determination in step S157 are repeated.

[0147] When it is determined that the current bell crank angle θ2 has reached the target bell crank angle c by continuing the movement of the bucket 14 in the tilt direction (YES in step S157), the controller 50 ends the full tilt control in step S158. Returning to FIG. 5 , in step S16, the controller 50 ends the auto tip-off.

[0148] In the determination in step S6, if the target soil volume is equal to or greater than the post-excavation soil volume, that is, if the load mass, which is the mass of the excavation target in the bucket 14 after excavation work, is equal to or less than the target value for the load mass in the bucket 14 (target load mass) (NO in step S6), it is not necessary to perform tip-off and adjust the load mass in the bucket 14. In this case, the process proceeds to step S16, and the controller 50 ends auto tip-off.

[0149] Upon completion of auto tip-off, automatic control of the work implement 3 may be released. When automatic control is released, the work implement 3 operates in accordance with manual operation of the operating lever for the work implement 3 by the operator. Alternatively, after completion of auto tip-off, the controller 50 may automatically perform loading work.

[0150] In the auto tip-off control process shown in Figure 5, the controller 50 proceeds to control of Step 2 after control of Step 1, and then proceeds to control of Step 3 after Step 2, or ends tip-off as is, but this example is not limited to this. Control of Step 2 does not necessarily have to be performed. After control of Step 1, control of Step 2 may be skipped and control of Step 3 may be executed. Processing may proceed directly from control of Step 1 to control of Step 3. Figure 15 is a flow chart for explaining another example of the flow of the auto tip-off control process. Differences between the process shown in Figure 15 and the process shown in Figure 5 will be described below.

[0151] In the process shown in FIG. 15, the current bucket ground angle θ Ｂ The target bucket angle θ Ｔ If the current bucket ground angle θ is equal to or greater than the predetermined value (NO in step S9), the process proceeds to step S21. Ｂ It is determined whether or not the angle .theta..times ...

[0152] In the determination of step S21, the current bucket ground angle θ ＢIf the current bucket ground angle θ is equal to or greater than 0° (NO in step S21), the process returns to step S8, and the controller 50 continues the control in step 1. Ｂ If the angle is smaller than 0° (YES in the determination of step S21), the controller 50 ends the control of step 1 and proceeds to the control of step 3. The process proceeds to step S13 via a connector A, and in step S13, the controller 50 performs the control of step 3.

[0153] Target bucket ground angle θ Ｔ With reference to the dashed line shown in table T1 in FIG. 8, if the target soil volume is 2 tons, the target bucket ground angle θ Ｔ In this case, the bucket 14 is moved in the dump direction to reduce the bucket ground angle θ Ｂ As the bucket ground angle θ decreases, Ｂ The target bucket angle θ Ｔ Before reaching (-20°), the current bucket ground angle θ Ｂ In this case, as shown in Fig. 15, the control of Step 2 in step S10 is not performed, and the process moves directly from the control of Step 1 to the control of Step 3.

[0154] <Functions and Effects> The characteristic configuration and functions and effects of this embodiment are summarized below.

[0155] As shown in FIG. 8, the auto tip-off control unit 512 of the controller 50 controls the load mass and the bucket ground angle θ Ｂ Using table T1 showing the relationship between the target bucket ground angle θ Ｔ The auto tip-off control unit 512 determines the target bucket ground angle θ Ｔ The bucket 14 is moved in the dump direction toward the target.

[0156] This bucket angle θ ＢThe relationship between the load mass in the bucket 14 and the target load mass is determined in advance. A table T1 showing this relationship is stored in the storage unit 500. By applying the target load mass to the table T1, the target bucket ground angle θ Ｔ Determine the target bucket ground angle θ Ｔ The speed at which the bucket 14 is dumped is increased until the bucket 14 reaches the target bucket ground angle θ . By setting a speed-up range where the load in the bucket 14 can be roughly dumped without any adverse effect, the controller 50 can adjust the bucket 14 to the target bucket ground angle θ . Ｔ This shortens the time it takes to move the bucket 14 toward the target position, thereby shortening the time it takes to unload the load from the bucket 14. This allows tip-off to be performed automatically in a short time.

[0157] As shown in FIG. 8, the bucket ground angle θ when the bucket 14 is tilted back from the attitude when the excavation target of the target load mass is accommodated in the bucket 14 is Ｂ The target bucket ground angle θ Ｔ The target bucket ground angle θ Ｔ The speed of the bucket 14 is increased until it reaches the target bucket ground angle θ Ｔ The speed of the bucket 14 is reduced after reaching the predetermined speed. In this way, tip-off can be performed automatically with high accuracy in a short time.

[0158] As shown in Figure 5, the auto tip-off control unit 512 of the controller 50 may operate the bucket 14 in the dump direction when the load mass after the excavation operation is greater than the target load mass. If the load mass after the excavation operation is equal to or less than the target load mass, tip-off, which discharges the load in the bucket 14, may not be performed. The controller 50 determines whether it is necessary to discharge the load in the bucket 14 and adjust the load mass, and if the load mass is the target load mass and no adjustment of the load mass is necessary, it controls not to perform tip-off. This makes it possible to prevent the load in the bucket 14 from being reduced too much.

[0159] As shown in FIG. 13, the auto tip-off control unit 512 of the controller 50 controls the target bucket ground angle θ ＴAlternatively, the bucket 14 may be operated at a constant speed toward the target point. If an attempt is made to set the speed of the bucket 14 based on the load mass calculated while the instantaneous value of the load mass is pulsating, the operation of the bucket 14 may become unstable. By controlling the bucket 14 to operate at a constant speed, the bucket 14 can be operated stably, and the productivity of the excavation and loading work can be stabilized. By setting the speed of the bucket 14 to a sufficiently large constant speed, the controller 50 can adjust the bucket 14 to the target bucket ground angle θ Ｔ Therefore, the time required for moving the object toward the target can be reliably shortened.

[0160] As shown in FIG. 8, the auto tip-off control unit 512 of the controller 50 controls the target bucket ground angle θ Ｔ The speed of the bucket 14 moving toward the target load mass may be determined based on the target load mass. When the target load mass is small, the movement amount of the bucket 14 until the load mass in the bucket 14 reaches the target load mass increases. By controlling the bucket 14 to perform the dump operation at a higher speed when the target load mass is small, it is possible to prevent the time required for tip-off from becoming longer depending on the target load mass.

[0161] As shown in FIGS. 5 and 8 to 10, the auto tip-off control unit 512 of the controller 50 controls the target bucket ground angle θ Ｔ After reaching the target bucket angle θ, the bucket 14 may be continuously moved in the dump direction. Ｔ The bucket 14 is dumped at high speed until it reaches the target bucket ground angle θ Ｔ After reaching the target load mass, the bucket 14 is dumped so as to accurately reduce the load mass to the target load mass. This allows automatic tip-off to be performed with high accuracy in a short time.

[0162] As shown in FIG. 13, the auto tip-off control unit 512 of the controller 50 controls the target bucket ground angle θ Ｔ The speed of the bucket 14 after reaching the target bucket ground angle θ Ｔ The speed of the bucket 14 may be smaller than the speed at which the bucket 14 reaches the target ground angle θ. ＴThe bucket 14 is dumped at high speed until it reaches the target bucket ground angle θ Ｔ After reaching the target load mass, the bucket 14 is dumped at a slower speed, and the load mass is accurately reduced to the target load mass. This allows for automatic tip-off with high accuracy in a short period of time.

[0163] As shown in FIGS. 9 and 10, the auto tip-off control unit 512 of the controller 50 controls the target bucket ground angle θ Ｔ The speed of the bucket 14 after reaching the target load mass may be determined based on the current load mass and the target load mass. By determining the speed of the bucket 14 in this manner, the bucket 14 can be dumped so as to accurately reduce the load mass to the target load mass.

[0164] As shown in FIGS. 9 and 10, the auto tip-off control unit 512 of the controller 50 controls the target bucket ground angle θ Ｔ The speed of the bucket 14 after reaching the target load mass may be determined based on the magnitude of the difference between the current load mass and the target load mass. By reducing the speed of the bucket 14 as the current load mass approaches the target load mass, the bucket 14 can be dumped so as to accurately reduce the load mass to the target load mass.

[0165] As shown in FIGS. 5 and 11, the auto tip-off control unit 512 of the controller 50 calculates the current bucket ground angle θ Ｂ After the bucket ground angle θ becomes smaller than 0°, the bucket 14 may be continuously moved in the dump direction. Ｂ When the bucket ground angle θ is smaller than 0°, the bucket 14 is in a position that actively drops the load in the bucket 14 from the cutting edge 14a. Ｂ After the angle becomes smaller than 0°, the bucket 14 is dumped so as to accurately reduce the load mass to the target load mass. This allows for automatic tip-off with high accuracy.

[0166] As shown in FIG. 13, the auto tip-off control unit 512 of the controller 50 controls the bucket to ground angle θ ＢThe speed of the bucket 14 after the bucket ground angle θ becomes smaller than 0° is defined as Ｂ The speed of the bucket 14 may be slower than that when the bucket ground angle θ is 0° or greater. Ｂ After the angle becomes smaller than 0°, the bucket 14 is dumped at a slower speed, and the load mass is controlled to be accurately reduced to the target load mass. This allows for automatic tip-off with high accuracy.

[0167] As shown in FIG. 15, the auto tip-off control unit 512 of the controller 50 controls the target bucket ground angle θ Ｔ The current bucket ground angle θ Ｂ becomes smaller than 0°, the bucket 14 continues to move in the dump direction, and the bucket ground angle θ Ｂ The speed of the bucket 14 after the bucket ground angle θ becomes smaller than 0° is defined as Ｂ The speed of the bucket 14 may be slower than that when the bucket ground angle θ is 0° or greater. Ｂ is 0° or more, the bucket 14 is dumped at high speed, and the bucket ground angle θ Ｂ After the angle becomes smaller than 0°, the bucket 14 is dumped at a slower speed to accurately reduce the load mass to the target load mass. This allows for automatic tip-off with high accuracy in a short period of time.

[0168] As shown in FIG. 12, the auto tip-off control unit 512 of the controller 50 controls the bucket to ground angle θ Ｂ After the bucket ground angle θ becomes smaller than 0°, the bucket 14 may be operated so that the rate of decrease in the load mass becomes constant. Ｂ When the bucket ground angle θ is less than 0°, the bucket 14 is in a position where the load falls from the cutting edge 14a. Ｂ By decreasing the speed of the bucket 14 as the absolute value of θ increases, the rate at which the load mass decreases can be made constant. In this way, the end of tipping-off can be determined with higher accuracy. The smaller the target load mass, the more accurate tipping-off can be performed automatically with this control.

[0169] 5 and 14 , the auto tip-off control unit 512 of the controller 50 may raise the boom 15 while moving the bucket 14 in the dump direction. By calculating the load mass while the boom 15 is being raised, the load mass can be calculated more accurately.

[0170] 5 and 14, when the auto tip-off control unit 512 of the controller 50 determines that the load mass in the bucket 14 has been reduced, it moves the bucket 14 in the tilt direction. The load mass is reduced by causing the load in the bucket 14 to fall from the cutting edge 14a. During the operation of reducing the load mass, the load in the bucket 14 is biased toward the front (toward the cutting edge 14a). By moving the bucket 14 in the tilt direction once the load mass in the bucket 14 has been reduced, the load in the bucket 14 can be moved rearward, improving the load shape in the bucket 14. This makes it possible to prevent the load from spilling from the bucket 14 when the wheel loader 1 travels after tip-off.

[0171] 5 and 14, the auto tip-off control unit 512 of the controller 50 may perform full tilt control, which moves the bucket 14 in the tilt direction up to the full tilt state. Referring to FIG. 1, when the bucket 14 is in the full tilt state, the bucket ground angle θ Ｂ takes a positive value, the back surface 14b of the bucket 14 is inclined with respect to the ground surface G so as to approach the ground surface G as it moves away from the cutting edge 14a, and the cutting edge 14a of the bucket 14 is positioned above the bucket pin 22. By placing the bucket 14 in a fully tilted state, the load in the bucket 14 can be reliably moved rearward, and the state of the load in the bucket 14 can be improved.

[0172] 14, the auto tip-off control unit 512 of the controller 50 may move the bucket 14 in the tilt direction at at least two different speeds. By moving the bucket 14 in the tilt direction at high speed, it is possible to reliably improve the shape of the load inside the bucket 14. By moving the bucket 14 at a low speed, it is possible to reduce the change in speed when the bucket 14 stops, thereby reducing the impact.

[0173] 14, the auto tip-off control unit 512 of the controller 50 may set the speed of the bucket 14 after the bell crank angle θ2 reaches the angle (c-β) to be slower than the speed of the bucket 14 before the bell crank angle θ2 reaches the angle (c-β). By moving the bucket 14 in the tilt direction at high speed until the bell crank angle θ2 reaches the angle (c-β), it is possible to reliably improve the shape of the load in the bucket 14. By moving the bucket 14 in the tilt direction at low speed after the bell crank angle θ2 reaches the angle (c-β), it is possible to reduce the impact when the bucket 14 stops.

[0174] As shown in FIG. 5 , the auto tip-off control unit 512 of the controller 50 may operate the bucket 14 in the dump direction to reduce the load mass in the bucket 14. By operating the bucket 14 in the dump direction, the load in the bucket 14 falls from the cutting edge 14a, reducing the load mass. Operating the bucket 14 in the dump direction causes the load in the bucket 14 to be biased toward the cutting edge 14a. After the load mass in the bucket 14 has been reduced, operating the bucket 14 in the tilt direction can move the load in the bucket 14 rearward, improving the state of the load in the bucket 14.

[0175] 5, the auto tip-off completion determination unit 513 of the controller 50 may determine that the load mass reduction has finished when the current load mass reaches a threshold value obtained by adding the target soil volume to the mass α. By setting a threshold value, the timing for determining that the load mass reduction has finished can be clarified, and the controller 50 can start the tilting movement of the bucket 14 at the appropriate timing.

[0176] The threshold value for determining that the load mass has been reduced may be any value determined from the target soil volume. The threshold value may be a value different from the target soil volume. The threshold value does not necessarily have to be a constant value. If the threshold value is the target soil volume plus the mass α, the value α may be increased if the rate of reduction of the load mass is high, so that the bucket 14 starts to move in the tilt direction earlier. This makes it possible to prevent the bucket 14 from dumping too much of the load.

[0177] In the auto tip-off embodiment, an example has been described in which the processing of Step 1 is performed, followed by the processing of either or both of Step 2 and Step 3. The processing of Step 1 may be omitted. Simultaneously with the start of auto tip-off, control of Step 2 may be performed to determine the speed of the bucket 14 based on the magnitude of the difference between the current load mass and the target load mass.

[0178] The work machine does not have to be operated by an operator inside the cab 5. The work machine may be remotely controlled by radio from a location away from the work site. By having the controller 50 mounted on the work machine automatically perform tip-off, the effects of response delays that can occur when manually operating from a remote location can be eliminated, enabling highly accurate tip-off.

[0179] <Additional Notes> The above description includes the following additional features.

[0180] (Supplementary Note 1) A work machine comprising: a vehicle body; a work machine attached to the vehicle body and having a bucket at its tip; and a controller that commands the operation of the work machine, wherein the controller operates the bucket to reduce a load mass in the bucket so that the load mass approaches a target load mass that is a target value for the load mass, and when it determines that the load mass has been reduced, operates the bucket in a tilt direction.

[0181] (Supplementary Note 2) The work machine according to Supplementary Note 1, wherein the controller operates the bucket to a full tilt state.

[0182] (Supplementary Note 3) The work machine according to Supplementary Note 1 or Supplementary Note 2, wherein the controller moves the bucket in the tilt direction at at least two different speeds.

[0183] (Supplementary Note 4) The work machine according to Supplementary Note 3, wherein the controller makes the speed of the bucket after the bucket has reached a predetermined bucket attitude slower than the speed of the bucket before the bucket has reached the predetermined bucket attitude.

[0184] (Supplementary Note 5) The work machine according to any one of Supplementary Note 1 to Supplementary Note 4, wherein the controller operates the bucket in a dump direction to reduce the load mass.

[0185] (Supplementary Note 6) The work machine according to any one of Supplementary Note 1 to Supplementary Note 5, wherein the controller determines that the load mass has been reduced when the current load mass reaches a predetermined threshold determined by the target load mass.

[0186] The embodiments disclosed herein are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0187] 1 Wheel loader, 2 Body frame, 3 Work machine, 4 Traveling device, 5 Cab, 9 Machine body, 14 Bucket, 14a Cutting edge, 14b Back, 15 Boom, 16 Bell crank, 18 Boom cylinder, 19 Bucket cylinder, 21 Boom foot pin, 22 Bucket pin, 31b, 31h, 32b, 32h Pressure sensor, 33, 34 Potentiometer, 35, 36 Stroke sensor, 39 Imaging device, 40 Angle sensor, 50 Controller, 51 Input unit, 52 Display unit, 100 Excavation target, 500 Memory unit, 501 Boom cylinder thrust calculation unit, 502 Hydraulic transmission efficiency calculation unit, 503 Dimension value calculation unit, 505 Bucket ground angle calculation unit, 508 Target load mass calculation unit, 509 Load mass calculation unit, 510 Automatic tip-off control unit, 511 Auto tip-off start determination unit, 512 auto tip-off control unit, 513 auto tip-off end determination unit.

Claims

1. A work machine comprising: a vehicle body; a work machine attached to the vehicle body and having a bucket at its tip; and a controller that commands the operation of the work machine, wherein the controller operates the bucket to reduce the load mass in the bucket so that the load mass approaches a target load mass, which is a target value for the load mass, and when it determines that the load mass has been reduced, operates the bucket in a tilt direction.

2. The work machine according to claim 1, wherein the controller operates the bucket to a full tilt state.

3. A work machine according to claim 1 or 2, wherein the controller operates the bucket in the tilt direction at at least two different speeds.

4. The work machine according to claim 3, wherein the controller makes the velocity of the bucket after the predetermined bucket attitude is reached slower than the velocity of the bucket before the predetermined bucket attitude is reached.

5. The work machine according to claim 1 or 2, wherein the controller operates the bucket in a dump direction to reduce the load mass.

6. A work machine as set forth in claim 1 or claim 2, wherein the controller determines that the load mass reduction has been completed when the current load mass reaches a predetermined threshold determined by the target load mass.

7. A system including a work machine comprising a vehicle body and a work implement attached to the vehicle body and having a bucket at its tip; and a controller that commands the operation of the work implement, wherein the controller operates the bucket to reduce the load mass in the bucket so that the load mass approaches a target load mass, which is a target value for the load mass, and operates the bucket in a tilt direction when it determines that the load mass has been reduced.

8. A control method for a work machine, comprising: operating the bucket at the tip of the work machine to reduce the load mass in the bucket so that the load mass approaches a target load mass, which is a target value; and operating the bucket in a tilt direction when it is determined that the load mass has been reduced.

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