Wheel loader

Abstract

To provide a wheel loader capable of accurately and easily performing loading work with an arbitrary loading weight by accurately calculating the loaded load of a bucket during the loading work.SOLUTION: A wheel loader 1 comprises a load calculation device 32 calculates thrust force of a lift cylinder 7 and a bucket cylinder 8 from the measured values of a lift pressure sensor 25 and a bucket pressure sensor 26, and calculates the load of a bucket 3 based on the calculated thrust. The load calculation device 32 calculates the loaded load of the bucket 3 during the loading work based on the difference value obtained by subtracting the thrust force of the lift cylinder 7 and the thrust force of the bucket cylinder 8 when the same operation as during the loading work is performed with the bucket 3 in an empty state from the thrust force of the lift cylinder 7 and the thrust force of the bucket cylinder 8 during the loading work in which the bucket 3 is loaded and the dump operation and the lift operation are performed.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a wheel loader.

Background Art

[0002] When loading work is performed from a wheel loader to a loading machine such as a dump truck, in order to observe the loading limit of the loading machine, loading with an appropriate loading weight is required. Some wheel loaders are provided with a device for calculating the loading weight in the bucket (for example, Patent Document 1).

[0003] The wheel loader described in Patent Document 1 calculates the no-load moment, which is the moment around the hinge pin connecting the lift arm and the vehicle body in the no-load state of the bucket, and calculates the load moment, which is the moment around the hinge pin in the loaded state of the bucket. The wheel loader described in Patent Document 1 calculates the loading weight of the bucket by dividing the difference between the no-load moment and the load moment by the horizontal distance between the center of gravity position of the bucket and the hinge pin.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the wheel loader described in Patent Document 1, when the bucket rotates and the center of gravity position changes as in the loading operation, the calculation error of the loading load becomes large. It is difficult to apply the wheel loader described in Patent Document 1 when calculating the loading load of the bucket during the loading operation. In order to comply with the loading limit of the machine to be loaded, the wheel loader may sometimes have to load only a part of the load in the bucket onto the machine to be loaded with the correct loading weight. To load only a part of the load in the bucket onto the machine to be loaded with the correct loading weight, the skill of a skilled operator is required.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a wheel loader capable of accurately and easily performing a loading operation with an arbitrary loading weight by accurately calculating the loading load of a bucket during the loading operation.

Means for Solving the Problems

[0007] In order to solve the above problems, the wheel loader of the present invention includes a lift arm rotatably connected to a vehicle body, a lift cylinder that performs a lift-up operation of rotating the lift arm upward and a lift-down operation of rotating the lift arm downward, a bucket rotatably connected to the lift arm, a bucket cylinder that performs a tilt operation of rotating the bucket upward and a dump operation of rotating the bucket downward, a lift pressure sensor that measures the pressure of the lift cylinder, a bucket pressure sensor that measures the pressure of the bucket cylinder, a load calculation device that calculates the thrust of the lift cylinder and the thrust of the bucket cylinder from the measured values of the lift pressure sensor and the bucket pressure sensor respectively, and calculates the loading load of the bucket based on the calculated thrust of the lift cylinder and the thrust of the bucket cylinder. The load calculation device calculates the loading load during the loading operation based on the difference values obtained by subtracting the thrust of the lift cylinder and the thrust of the bucket cylinder when the same operations as those during the loading operation are performed with the bucket in an empty load state from the thrust of the lift cylinder and the thrust of the bucket cylinder during the loading operation with the bucket in a loaded state.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a wheel loader capable of accurately and easily performing a loading operation with an arbitrary loading weight by accurately calculating the loading load of the bucket during the loading operation. Problems, configurations, and effects other than those described above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. For components denoted by the same reference numerals in each embodiment, unless otherwise specified, they have the same functions in each embodiment and the description thereof will be omitted.

[0011] FIG. 1 is a diagram showing the configuration of the wheel loader 1 of the present embodiment. FIG. 2 is a diagram for explaining the lift angle and the bell crank angle.

[0012] The wheel loader 1 is a construction machine that performs a loading operation of loading the load such as earth and sand excavated by the bucket 3 onto a loading machine such as a dump truck. Wheels 4 capable of traveling on uneven ground and sloping ground are provided at the lower parts of the front body 11 and the rear body 12 of the wheel loader 1. A cab 5 is provided on the upper part of the rear body 12 of the wheel loader 1. An operating device operated by an operator is provided in the cab 5. The operating device is, for example, a steering wheel for operating the steering angle of the wheels 4, an operating lever for operating the rotation of the lift arm 2 and the bucket 3, a semi-automatic loading button 28 (Fig. 3) which is a switch for causing the wheel loader 1 to perform the loading operation semi-automatically, a target loading weight input unit 27 (Fig. 3) for inputting a target value of the loading weight onto the loading machine (hereinafter also referred to as "target loading weight"), and the like. An engine room 6 is provided at the rear part of the rear body 12 behind the cab 5. An engine 21, a hydraulic main pump 22, and the like are provided in the engine room 6.

[0013] A pair of left and right lift arms 2 extending forward from the front part of the front body 11 are rotatably connected to the front body 11 of the wheel loader 1 in the vertical direction. The middle part of the lift arm 2 and the front body 11 are connected by a lift cylinder 7. When pressure oil is supplied to the cap chamber (bottom chamber) of the lift cylinder 7, the stroke of the rod 7a extends and the lift arm 2 rotates upward (hereinafter also referred to as "lift-up operation"). When pressure oil (hydraulic oil) is supplied to the rod chamber of the lift cylinder 7, the stroke of the rod 7a retracts and the lift arm 2 rotates downward (hereinafter also referred to as "lift-down operation").

[0014] A bucket 3 is rotatably connected to the tip of a lift arm 2. A bell crank 9 is connected to the bucket 3 via a bucket link 10. The bell crank 9 is connected to a bucket cylinder 8 that extends forward from the front part of a front body 11. The bell crank 9 connects the bucket 3 and the bucket cylinder 8 via the bucket link 10 and transmits the thrust of the bucket cylinder 8 to the bucket 3. When pressure oil is supplied to the cap chamber (bottom chamber) of the bucket cylinder 8, the stroke of a rod 8a extends and the bucket 3 rotates upward (hereinafter also referred to as a "tilt operation"). When pressure oil is supplied to the rod chamber of the bucket cylinder 8, the stroke of the rod 8a retracts and the bucket 3 rotates downward (hereinafter also referred to as a "dump operation"). The lift arm 2 and the bucket 3 constitute a working device of a wheel loader 1.

[0015] A lift angle sensor 13 is provided between the lift arm 2 and the front body 11. The lift angle sensor 13 measures a lift angle (θl) formed by the lift arm 2 with respect to the front body 11. The lift angle can be defined as an angle at which a line segment connecting a hinge pin 2a that connects the base end of the lift arm 2 and the front body 11 and a hinge pin 2b that connects the tip of the lift arm 2 and the bucket 3 rotates around the hinge pin 2a. The lift angle can be defined with the state before rotation of the lift arm 2 with the rod 7a retracted as shown in FIG. 2 as 0 degrees, and the direction in which the lift arm 2 rotates upward as positive.

[0016] A bell crank angle sensor 14 is provided between the lift arm 2 and the bell crank 9. The bell crank angle sensor 14 measures a bell crank angle (θb) formed by the bell crank 9 with respect to the lift arm 2. The bell crank angle can be defined as an angle at which a line segment connecting a hinge pin 8b that connects the rod 8a of the bucket cylinder 8 and the base end of the bell crank 9 and a hinge pin 2c that connects the middle part of the lift arm 2 and the middle part of the bell crank 9 rotates around the hinge pin 2c. The bell crank angle can be defined with the state in which the bell crank 9 stands upright as shown in FIG. 2 as 0 degrees, and the direction in which the bell crank 9 rotates counterclockwise as positive.

[0017] Figure 3 is a block diagram showing the functional configuration of the wheel loader 1 shown in Figure 1. In Figure 3, thin solid lines indicate electrical signal lines, thick solid lines indicate pressure oil lines, and dashed lines indicate pilot lines. Figure 4 is a diagram for explaining the thrust of the lift cylinder 7 calculated by the no-load cylinder thrust calculation unit 35 shown in Figure 3. Figure 5 is a diagram for explaining the thrust of the bucket cylinder 8 calculated by the no-load cylinder thrust calculation unit 35 shown in Figure 3. Figure 6 is a diagram for explaining the tilt angle αt and the dump angle αd.

[0018] The wheel loader 1 includes a lift pressure sensor 25 that measures the pressure of the lift cylinder 7 and a bucket pressure sensor 26 that measures the pressure of the bucket cylinder 8. The lift pressure sensor 25 may be composed of a cap-side sensor 25a that measures the pressure of the cap chamber of the lift cylinder 7 and a rod-side sensor 25b that measures the pressure of the rod chamber of the lift cylinder 7. The measured value of the lift pressure sensor 25 may be the measured values of the cap-side sensor 25a and the rod-side sensor 25b. The bucket pressure sensor 26 may be composed of a cap-side sensor 26a that measures the pressure of the cap chamber of the bucket cylinder 8 and a rod-side sensor 26b that measures the pressure of the rod chamber of the bucket cylinder 8. The measured value of the bucket pressure sensor 26 may be the measured values of the cap-side sensor 26a and the rod-side sensor 26b.

[0019] The wheel loader 1 is configured to include a processor and a memory, and is provided with an arithmetic control unit 30 that realizes various functions of the wheel loader 1. When the operator presses the semi-automatic loading button 28, the arithmetic control unit 30 executes a process of causing the work equipment to perform the loading work semi-automatically (hereinafter also referred to as "semi-automatic loading process"). Specifically, when the semi-automatic loading button 28 is pressed for the first time, the arithmetic control unit 30 automatically performs preparations before starting the loading work. When the semi-automatic loading button 28 is pressed for the second time, the arithmetic control unit 30 automatically starts the loading work. When the loading weight of the load onto the machine to be loaded reaches the target loading weight, the arithmetic control unit 30 automatically ends the loading work. As preparations before starting the loading work, the wheel loader 1 extends the bucket cylinder 8 with the excavated load loaded in the bucket 3 and changes from the full tilt posture with the opening of the bucket 3 facing upward to raise the bucket 3 to a height (hereinafter referred to as "loading start height") at which a predetermined loading work starts according to the height of the machine to be loaded and stops it. Then, when starting the loading work, the wheel loader 1 performs a dump operation and a lift-up operation on the bucket 3 that is in the loaded state, maintains the full tilt posture, and is positioned at the loading start height.

[0020] The arithmetic control unit 30 receives the measured values of the lift pressure sensor 25 and the bucket pressure sensor 26, the measured values of the lift angle sensor 13 and the bell crank angle sensor 14, the target loading weight input to the target loading weight input unit 27, and a signal indicating the pressing of the semi-automatic loading button 28.

[0021] The arithmetic control unit 30 includes a load arithmetic unit 32 that calculates the loading weight of the bucket 3 based on the above measured values and the signal from the semi-automatic loading button 28, and a control unit 31 that controls the operations of the lift cylinder 7 and the bucket cylinder 8 based on the loading weight of the bucket 3, the target loading weight, and the signal from the semi-automatic loading button 28.

[0022] The control device 31 calculates the target pilot pressures of the lift cylinder 7 and the bucket cylinder 8, and controls the operations of the lift cylinder 7 and the bucket cylinder 8 by outputting a control signal for achieving the target pilot pressure to the pilot valve 24. The pilot valve 24 adjusts the discharge flow rate of the pilot pump according to the target pilot pressure to adjust the pilot pressure, and operates the control valve 23. The control valve 23 opens with an opening degree corresponding to the pilot pressure, and supplies the pressure oil discharged from the main pump 22 driven by the engine 21 to the cap chamber and the rod chamber of the lift cylinder 7, and the cap chamber and the rod chamber of the bucket cylinder 8. Thereby, the strokes of the lift cylinder 7 and the bucket cylinder 8 change, and the operations of the lift arm 2 and the bucket 3 constituting the working device of the wheel loader 1 are controlled.

[0023] The load calculation device 32 calculates the thrusts of the lift cylinder 7 and the bucket cylinder 8 from the measured values of the lift pressure sensor 25 and the bucket pressure sensor 26, and calculates the loading load of the bucket 3 based on the calculated thrusts. In particular, the load calculation device 32 calculates the loading load of the bucket 3 during the loading operation based on the difference value obtained by subtracting the thrusts when the bucket 3 is in the unloaded state and performs the same operation as during the loading operation from the thrusts during the loading operation when the bucket 3 is in the loaded state. The thrust of the lift cylinder 7 can be calculated from the difference between the product of the measured value of the cap side sensor 25a of the lift pressure sensor 25 and the pressure receiving area of the cap chamber and the product of the measured value of the rod side sensor 25b and the pressure receiving area of the rod chamber. The thrust of the bucket cylinder 8 can also be calculated in the same manner as the thrust of the lift cylinder 7.

[0024] The load calculation device 32 includes a pre-loading load calculation unit 33, a loading load calculation unit 34, an unloaded cylinder thrust calculation unit 35, a load correction unit 36, and a load output unit 37.

[0025] When the semi-automatic loading button 28 is pressed for the first time, the pre-loading load calculation unit 33 calculates the loading load of the bucket 3 in the state before the start of the loading operation of the wheel loader 1. The state before the start of the loading operation is the loaded state, and it is the state before performing the dump operation and the lift operation on the bucket 3 that maintains the full tilt posture and is positioned at the loading start height. That is, the state before the start of the loading operation is, for example, the state in which the bucket 3 with the full tilt posture is loaded with the load and is raised to the loading start height and stationary. In the stationary bucket 3, the bucket 3 is positioned at the loading start height while maintaining the full tilt posture by the bucket cylinder 8 with a certain stroke, the center of gravity position of the bucket 3 does not change, and the loading load of the bucket 3 is constant.

[0026] The pre-loading load calculation unit 33 calculates the thrust of the lift cylinder 7 in the state before the start of the loading operation. Then, the pre-loading load calculation unit 33 calculates the difference value obtained by subtracting the thrust calculated when the bucket 3 is in the unloaded state and in the same state as the state before the start of the loading operation from the calculated thrust. Then, the pre-loading load calculation unit 33 calculates the moment acting on the lift arm 2 from the calculated difference value, and divides the calculated moment by the horizontal distance of the lift arm 2. Thereby, the pre-loading load calculation unit 33 can calculate the loading load of the bucket 3 in the state before the start of the loading operation. The thrust of the lift cylinder 7 calculated when the bucket 3 is in the unloaded state and in the same state as the state before the start of the loading operation is calculated and stored in advance by the unloaded cylinder thrust calculation unit 35.

[0027] Note that the pre-loading load calculation unit 33 can calculate the loading load of the bucket 3 in the state before the start of the loading operation using the following method. That is, the pre-loading load calculation unit 33 calculates the loading load of the bucket 3 multiple times while the bucket 3 in the loaded state and maintaining the full tilt posture is being raised to the loading start height, and sets the average value as the loading load of the bucket 3 in the state before the start of the loading operation. Thereby, the pre-loading load calculation unit 33 can reduce the influence of the static friction force of the lift cylinder 7, so that the loading load of the bucket 3 in the state before the start of the loading operation can be calculated more accurately.

[0028] When the semi-automatic loading button 28 is pressed for the second time, the in-loading load calculation unit 34 calculates the loading load of the bucket 3 during the loading operation of the wheel loader 1. The "during the loading operation" means the period when the dumping operation and the lifting operation are being performed on the bucket 3 in the loaded state and maintaining the full tilt posture and located at the loading start height. During the loading operation, the bucket 3 rotates, the center of gravity position of the bucket 3 changes, and the loaded goods are discharged from the bucket 3, so the loading load of the bucket 3 changes. During the loading operation, the lift angle measured by the lift angle sensor 13 and the bell crank angle measured by the bell crank angle sensor 14 change.

[0029] The in-loading load calculation unit 34 calculates the thrusts of the lift cylinder 7 and the bucket cylinder 8 according to the lift angle and the bell crank angle that change during the loading operation. Then, the in-loading load calculation unit 34 calculates each difference value obtained by subtracting the thrusts calculated when the bucket 3 is in the unloaded state and performing the same operation as during the loading operation from the calculated thrusts. Then, the in-loading load calculation unit 34 calculates the moment acting on the lift arm 2 from the calculated difference values, and divides the calculated moment by the horizontal distance of the lift arm 2. Thereby, the in-loading load calculation unit 34 can calculate the loading load of the bucket 3 during the loading operation. The thrusts of the lift cylinder 7 and the bucket cylinder 8 calculated when the bucket 3 is in the unloaded state and performing the same operation as during the loading operation are calculated and stored in advance by the cylinder thrust calculation unit 35 for the unloaded state.

[0030] When the bucket 3 is in the no-load state, the cylinder thrust calculation unit 35 during loading operation calculates and stores the thrusts of the lift cylinder 7 and the bucket cylinder 8 according to the lift angle and the bell crank angle that change when the same operation as during the loading operation is performed. Further, the cylinder thrust calculation unit 35 during no-load calculates and stores the thrust of the lift cylinder 7 when the bucket 3 is in the no-load state and is in the same state as before the start of the loading operation. An example of each thrust stored in the cylinder thrust calculation unit 35 during no-load is shown in FIGS. 4 and 5. Each horizontal axis in FIGS. 4 and 5 indicates the bell crank angle. The vertical axis in FIG. 4 indicates the thrust of the lift cylinder 7 in the no-load state. The vertical axis in FIG. 5 indicates the thrust of the bucket cylinder 8 in the no-load state. Each thrust in FIGS. 4 and 5 is drawn as a plurality of graphs according to the lift angle. Thereby, when the lift angle and the bell crank angle are determined, the thrusts of the lift cylinder 7 and the bucket cylinder 8 are uniquely determined. Therefore, the cylinder thrust calculation unit 35 during no-load can specify the thrusts of the lift cylinder 7 and the bucket cylinder 8 when the same operation as during the loading operation is performed in the no-load state or when the same state as before the start of the loading operation is set in the no-load state.

[0031] Note that it is preferable that the cylinder thrust calculation unit 35 during no-load operation calculates the thrusts of the lift cylinder 7 and the bucket cylinder 8 when performing the same operation as during the loading operation in the no-load state using the following method. That is, the cylinder thrust calculation unit 35 during no-load operation raises the bucket 3 in the no-load state and maintaining the full tilt posture to the loading start height, and then while performing the dumping operation, acquires the measured values of the lift pressure sensor 25 and the bucket pressure sensor 26, calculates the respective thrusts from the acquired measured values, and stores them. Next, the cylinder thrust calculation unit 35 during no-load operation performs a lift-up operation by a predetermined lift angle, and while performing the dumping operation, acquires the measured values of the lift pressure sensor 25 and the bucket pressure sensor 26, calculates the respective thrusts from the acquired measured values, and stores them. These are repeated. That is, the cylinder thrust calculation unit 35 during no-load operation acquires the measured values of the lift pressure sensor 25 and the bucket pressure sensor 26 during the dumping operation on the bucket 3 in the no-load state, calculates the respective thrusts from the acquired measured values, and stores them.

[0032] In the lift cylinder 7 and the bucket cylinder 8, even if they stop at the same position when stopped after extension and when stopped after retraction, and the same load is applied, the pressure in the cap chamber and the pressure in the rod chamber may be different due to the influence of the direction of the static friction force. By using the above method, the cylinder thrust calculation unit 35 during no-load operation can make the influence of the static friction force of the lift cylinder 7 and the bucket cylinder 8 the same as during the loading operation. Thereby, the cylinder thrust calculation unit 35 during no-load operation can calculate the thrusts of the lift cylinder 7 and the bucket cylinder 8 more accurately when performing the same operation as during the loading operation in the no-load state. Also, when calculating the thrust of the lift cylinder 7 when the bucket 3 is in the no-load state and in the same state as before the start of the loading operation, the thrust of the lift cylinder 7 can be calculated more accurately by using the above method.

[0033] However, since the calculation by the in-loading load re-calculation unit 34 is performed while the center-of-gravity position of the bucket 3 changes, there is room for improvement in its accuracy compared to the calculation by the pre-loading load re-calculation unit 33 that is performed with the center-of-gravity position of the bucket 3 unchanged.

[0034] Therefore, the load correction unit 36 corrects the loading load of the bucket 3 during the loading operation calculated by the in-loading load re-calculation unit 34 based on the loading load of the bucket 3 in the state before the start of the loading operation calculated by the pre-loading load re-calculation unit 33. Thereby, the load calculation device 32 can calculate the loading load of the bucket 3 during the loading operation more accurately.

[0035] Specifically, the load correction unit 36 corrects the loading load of the bucket 3 during the loading operation based on the ratio between the loading load of the bucket 3 in the state before the start of the loading operation and the loading load of the bucket 3 in the state immediately after the start of the loading operation. The state immediately after the start of the loading operation is the state after starting the dump operation and the lift-up operation with respect to the bucket 3 in the loaded state that maintains the full-tilt posture and is positioned at the loading start height, and before the load is actually discharged from the bucket 3. In the state immediately after the start of the loading operation, the center-of-gravity position of the bucket 3 may change, but the true weight of the load in the bucket 3 in the state immediately after the start of the loading operation is equal to the true weight of the load in the bucket 3 in the state before the start of the loading operation. The loading load of the bucket 3 in the state immediately after the start of the loading operation is calculated by the in-loading load re-calculation unit 34. The load correction unit 36 corrects the loading load of the bucket 3 during the loading operation by multiplying the ratio by the loading load of the bucket 3 during the loading operation. Thereby, the load calculation device 32 can calculate the loading load of the bucket 3 during the loading operation more accurately and easily.

[0036] When the semi-automatic loading button 28 is pressed for the first time, the load output unit 37 outputs the loading load of the bucket 3 in the state before the start of the loading operation calculated by the pre-loading load calculation unit 33 to the control device 31. When the semi-automatic loading button 28 is pressed for the second time, the load output unit 37 outputs the loading load of the bucket 3 during the loading operation corrected by the load correction unit 36 to the control device 31.

[0037] The control device 31 receives the loading load of the bucket 3 output from the load output unit 37, the target loading weight input to the target loading weight input unit 27, and a signal indicating the pressing of the semi-automatic loading button 28. Based on these inputs, the control device 31 controls the operations of the lift cylinder 7 and the bucket cylinder 8.

[0038] When the semi-automatic loading button 28 is pressed for the first time, since the calculation by the pre-loading load calculation unit 33 is started, the control device 31 controls the operation of the bucket cylinder 8 so that a tilting operation to put the bucket 3 in a full tilt posture is performed. Then, the control device 31 controls the operation of the lift cylinder 7 so that a lift-up operation to raise the bucket 3 to the loading start height is performed.

[0039] When the semi-automatic loading button 28 is pressed for the second time, the control device 31 calculates the loading load of the load remaining in the bucket 3 at the end of the loading operation (hereinafter also referred to as "target loading load"). The target loading load of the bucket 3 at the end of the loading operation can be calculated by subtracting the target loading weight input to the target loading weight input unit 27 from the loading load of the bucket 3 in the state before the start of the loading operation calculated by the pre-loading load calculation unit 33. Then, the control device 31 controls the operation of the bucket cylinder 8 so that a dumping operation to rotate the bucket 3 downward is performed while maintaining the loaded state and the full tilt posture and being positioned at the loading start height. At the same time, the control device 31 controls the operation of the lift cylinder 7 so that a lift-up operation to rotate the lift arm 2 upward is performed. At this time, the loading load of the bucket 3 during the loading operation is calculated by the in-loading load calculation unit 34.

[0040] The control device 31 adjusts the target pilot pressure to adjust the speed of the lifting operation so that the lifting operation is performed at a low speed (or a minute speed). As a result, as the frictional force of the lift cylinder 7, the dynamic frictional force becomes constant and dominant, and the static frictional force can be reduced as much as possible. Therefore, the loading weight calculation unit 34 during loading can calculate the loading weight of the bucket 3 during the loading operation more accurately.

[0041] When the loading weight of the bucket 3 during the loading operation reaches the target loading weight, the control device 31 controls the operation of the bucket cylinder 8 so that the dumping operation stops. Then, the control device 31 controls the operation of the bucket cylinder 8 so that a large tilting operation is performed to suppress the discharge of the loaded cargo from the bucket 3, and then a small dumping operation is performed again to such an extent that the loaded cargo is not discharged from the bucket 3. The tilting angle αt (for example, 15 degrees), which is the magnitude of the angle by which the bucket 3 rotates upward in the tilting operation, is larger than the dumping angle αd (for example, 10 degrees), which is the magnitude of the angle by which the bucket 3 rotates downward in the dumping operation, as shown in FIG. 6. The tilting angle αt and the dumping angle αd can be defined based on the direction in which the tip 3a disposed at the lower part of the tip of the bucket 3 extends. Thereafter, the control device 31 controls the operations of the bucket cylinder 8 and the lift cylinder 7 so that the dumping operation and the lifting operation stop. Thereby, the loading operation ends.

[0042] Immediately before the end of the loading operation Dump angle α dThe dumping operation alone is performed because the cylinder thrust calculation unit 35 during no-load calculates the thrusts of the lift cylinder 7 and the bucket cylinder 8 during the dumping operation. The in-loading medium load calculation unit 34 calculates the final loading weight of the bucket 3 during the dumping operation immediately before the end of the loading operation or in the state at the end of the loading operation. Thereby, the in-loading medium load calculation unit 34 can calculate the final loading weight of the bucket 3 by making the operating modes of the lift cylinder 7 and the bucket cylinder 8 the same as those during the calculation by the no-load cylinder thrust calculation unit 35. Therefore, the in-loading medium load calculation unit 34 can calculate the final loading weight of the bucket 3 more accurately.

[0043] FIG. 7 is a diagram showing the transition of each stroke of the lift cylinder 7 and the bucket cylinder 8 during the loading operation.

[0044] The stroke of the lift cylinder 7 increases when the lift-up operation is performed and decreases when the lift-down operation is performed. The stroke of the bucket cylinder 8 increases when the tilt operation is performed and decreases when the dumping operation is performed.

[0045] At the start time t0 of the loading operation, the stroke of the lift cylinder 7 is extended to such an extent that the bucket 3 is positioned at the start height of loading. When the loading operation starts, the lift cylinder 7 performs a lifting operation at a constant low speed. The stroke of the lift cylinder 7 increases monotonically. The control device 31 controls the speed of the lifting operation to be a constant speed equal to or higher than the minimum speed required for the stroke of the lift cylinder 7 to increase monotonically. Further, the control device 31 controls the speed of the lifting operation to be a constant speed required for the stroke of the lift cylinder 7 to be equal to or less than the maximum stroke Smax at the end time t3 of the loading operation. The fact that the stroke of the lift cylinder 7 reaches the maximum stroke Smax means that the height of the bucket 3 reaches the highest lift. Thereby, since the control device 31 can increase the stroke of the lift cylinder 7 monotonically from the start to the end of the loading operation, the dynamic frictional force of the lift cylinder 7 during the loading operation can be kept constant. The in-loading load calculation unit 34 can calculate the loading load of the bucket 3 during the loading operation more accurately. Note that the control device 31 may control the speed of the lifting operation based on the difference between the loading load of the bucket 3 in the state before the start of the loading operation and the target loading weight (i.e., the target loading load of the bucket 3 at the end of the loading operation).

[0046] At the start time t0 of the loading operation, the stroke of the bucket cylinder 8 is extended greatly so that the bucket 3 is in a fully tilted posture. When the loading operation starts, the bucket cylinder 8 performs a dumping operation. The stroke of the bucket cylinder 8 decreases monotonically. At the time t1 when the loading load of the bucket 3 during the loading operation reaches the target loading load, the bucket cylinder 8 performs a tilting operation. The stroke of the bucket cylinder 8 increases monotonically. At the time t2 when the tilting operation is performed by the tilting angle αt, the bucket cylinder 8 performs a dumping operation again. The stroke of the bucket cylinder 8 decreases monotonically. At the time t3 when the dumping operation is performed by the dumping angle αd, the bucket cylinder 8 stops the dumping operation.

[0047] When the dumping operation and the lifting operation are stopped and the loading operation is completed, the control device 31 outputs a signal indicating that the loading operation has been completed to the semi-automatic loading button 28. The semi-automatic loading button 28 resets the number of times it has been pressed. The wheel loader 1 can then perform the loading operation semi-automatically again.

[0048] Figure 8 is a flowchart of the semi-automatic loading process.

[0049] When the semi-automatic loading button 28 is pressed for the first time after being reset by the operator, the arithmetic control device 30 starts the semi-automatic loading process shown in Figure 8.

[0050] In step S1, the arithmetic control device 30 controls the operation of the bucket cylinder 8 so that the bucket 3 is tilted to the full tilt position.

[0051] In step S2, the arithmetic control device 30 controls the operation of the lift cylinder 7 so that the bucket 3 is lifted to the loading start height.

[0052] In step S3, the arithmetic control device 30 calculates the loading weight of the bucket 3 multiple times while the bucket 3 in the loaded state and maintaining the full tilt position is being lifted to the loading start height, and calculates the average value. Then, the arithmetic control device 30 sets the calculated average value as the loading weight (Wi) of the bucket 3 in the state before the start of the loading operation. The loading weight (Wi) of the bucket 3 in the state before the start of the loading operation is a constant load as described above and is calculated only from the thrust of the lift cylinder 7.

[0053] In step S4, when the bucket 3 has risen to the loading start height, the arithmetic control device 30 controls the operation of the lift cylinder 7 so that the lifting operation stops.

[0054] In step S5, the arithmetic control unit 30 determines whether or not the target loading weight (Wt) input by the operator to the target loading weight input unit 27 has been input. The arithmetic control unit 30 waits until the target loading weight (Wt) is input, and when it is input, it proceeds to step S6.

[0055] In step S6, the arithmetic control unit 30 determines whether or not the semi-automatic loading button 28 has been pressed for the second time after being reset by the operator. The arithmetic control unit 30 waits until the semi-automatic loading button 28 is pressed, and when it is pressed, it proceeds to step S7.

[0056] In step S7, the arithmetic control unit 30 calculates the target loading load (Wf) of the bucket 3 at the end of the loading operation. The arithmetic control unit 30 can calculate the target loading load (Wf) using the following equation (1). Wf = Wi - Wt …(1)

[0057] In step S8, the arithmetic control unit 30 controls the operation of the bucket cylinder 8 so that the dumping operation starts and controls the operation of the lift cylinder 7 so that the lifting operation starts in order to start the loading operation.

[0058] In step S9, the arithmetic control unit 30 calculates the loading load (Wd) of the bucket 3 in the state immediately after the start of the loading operation. The state immediately after the start of the loading operation is the state immediately after starting the dumping operation and the lifting operation with respect to the bucket 3 in the loaded state, maintaining the full tilt posture and positioned at the loading start height, and before the load is actually discharged from the bucket 3, although the center of gravity position of the bucket 3 may change.

[0059] In step S10, the arithmetic control unit 30 calculates the loading load (W) of the bucket 3 during the loading operation. The loading operation is the period during which the dumping operation and the lifting operation are being performed with respect to the bucket 3 in the loaded state, maintaining the full tilt posture and positioned at the loading start height.

[0060] In step S11, the arithmetic control device 30 corrects the loading weight (W) of the bucket 3 during the loading operation. The arithmetic control device 30 can correct the loading weight (W) of the bucket 3 during the loading operation by using the following formula (2). Let the corrected loading weight of the bucket 3 be W'. W' = W × (Wi / Wd) …(2)

[0061] In step S12, the arithmetic control device 30 determines whether the corrected loading weight (W') of the bucket 3 has reached the target loading weight (Wf). The arithmetic control device 30 can make the determination by using the following formula (3). If formula (3) is not satisfied, it means that the corrected loading weight (W') of the bucket 3 has not reached the target loading weight (Wf), so the arithmetic control device 30 proceeds to step S10. If formula (3) is satisfied, it means that the corrected loading weight (W') of the bucket 3 has reached the target loading weight (Wf), so the arithmetic control device 30 proceeds to step S13. W' ≤ Wf …(3)

[0062] In step S13, the arithmetic control device 30 controls the operation of the bucket cylinder 8 so that the tilting operation is performed by the tilting angle αt.

[0063] In step S14, the arithmetic control device 30 controls the operation of the bucket cylinder 8 so that the dumping operation is performed by the dumping angle αd.

[0064] In step S15, the arithmetic control device 30 controls the operation of the bucket cylinder 8 so that the dumping operation stops and controls the operation of the lift cylinder 7 so that the lifting operation stops in order to end the loading operation.

[0065] In step S16, the arithmetic control device 30 calculates the final loading weight of the bucket 3. Then, the arithmetic control device 30 ends the process shown in FIG. 8. Note that the arithmetic control device 30 may perform step S16 between step S14 and step S15.

[0066] As described above, the wheel loader 1 of the present embodiment includes a lift arm 2 rotatably connected to the front body 11, a lift cylinder 7 that performs a lift-up operation of rotating the lift arm 2 upward and a lift-down operation of rotating the lift arm 2 downward, a bucket 3 rotatably connected to the lift arm 2, a bucket cylinder 8 that performs a tilt operation of rotating the bucket 3 upward and a dump operation of rotating the bucket 3 downward, a lift pressure sensor 25 that measures the pressure of the lift cylinder 7, a bucket pressure sensor 26 that measures the pressure of the bucket cylinder 8, and a load calculation device 32 that calculates the thrust of the lift cylinder 7 and the thrust of the bucket cylinder 8 from the measured values of the lift pressure sensor 25 and the bucket pressure sensor 26, respectively, and calculates the loading load of the bucket 3 based on the calculated thrust of the lift cylinder 7 and the thrust of the bucket cylinder 8. The load calculation device 32 calculates the loading load of the bucket 3 during the loading operation based on the difference value obtained by subtracting the thrust of the lift cylinder 7 and the thrust of the bucket cylinder 8 when the same operations as those during the loading operation are performed with the bucket 3 in the empty load state from the thrust of the lift cylinder 7 and the thrust of the bucket cylinder 8 during the loading operation with the bucket 3 in the loaded state and performing the dump operation and the lift-up operation.

[0067] Thereby, even when the center of gravity position of the bucket 3 changes as in the case during the loading operation, the load calculation device 32 can accurately calculate the loading load of the bucket 3. When the wheel loader 1 loads only a part of the load in the bucket 3 onto the machine to be loaded, it can be loaded with an accurate loading weight without the skilled skill of the operator. Therefore, the wheel loader 1 of the present embodiment can accurately and easily perform the loading operation with an arbitrary loading weight.

[0068] Furthermore, the wheel loader 1 of the present embodiment further includes a bell crank 9 that connects the bucket 3 and the bucket cylinder 8 and transmits the thrust of the bucket cylinder 8 to the bucket 3, a lift angle sensor 13 that measures the lift angle formed by the lift arm 2 with respect to the front body 11, and a bell crank angle sensor 14 that measures the bell crank angle formed by the bell crank 9 with respect to the lift arm 2. The load calculation device 32 has an unloaded cylinder thrust calculation unit 35 that calculates and stores the thrust of the lift cylinder 7 and the thrust of the bucket cylinder 8 according to the lift angle and the bell crank angle that change when the bucket 3 is in an unloaded state and performs the same operation as during the loading operation. The load calculation device 32 calculates the thrust of the lift cylinder 7 and the thrust of the bucket cylinder 8 according to the lift angle and the bell crank angle that change during the loading operation with the bucket 3 in a loaded state, and calculates the above difference value by subtracting the thrust of the lift cylinder 7 and the thrust of the bucket cylinder 8 stored in the unloaded cylinder thrust calculation unit 35 from the calculated thrust of the lift cylinder 7 and the thrust of the bucket cylinder 8, respectively. Based on the calculated difference value, the load calculation device 32 has a loading load calculation unit 34 that calculates the loading load of the bucket 3 during the loading operation.

[0069] As a result, the states of the lift cylinder 7 and the bucket cylinder 8 when calculating the respective thrusts in the unloaded state of the bucket 3 are the same as the states of the lift cylinder 7 and the bucket cylinder 8 when calculating the respective thrusts during the loading operation. Therefore, the load calculation device 32 can appropriately calculate the respective thrusts in the unloaded state of the bucket 3, so that the loading load of the bucket 3 during the loading operation can be accurately calculated. Thus, the wheel loader 1 of the present embodiment can perform the loading operation with an arbitrary loading weight more accurately and easily.

[0070] [Others] Note that the present invention is not limited to the above-described embodiments and includes various modifications. For example, the above embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Also, part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, for part of the configuration of each embodiment, addition, deletion, or replacement with other configurations is possible.

[0071] In addition, each of the above configurations, functions, processing units, processing means, etc. may be realized by hardware, for example, by designing part or all of them using an integrated circuit. Also, each of the above configurations, functions, etc. may be realized by software by a processor interpreting and executing a program for realizing each function. Information such as a program, tape, file, etc. for realizing each function can be placed in a memory, a recording device such as a hard disk, SSD (solid state drive), or a recording medium such as an IC card, SD card, DVD.

[0072] Also, control lines and information lines show those considered necessary for explanation, and not necessarily all control lines and information lines are shown on the product. In fact, it may be considered that almost all configurations are interconnected.

Explanation of Reference Numerals

[0073] 1... Wheel loader, 2... Lift arm, 3... Bucket, 7... Lift cylinder, 8... Bucket cylinder, 9... Bell crank, 11... Front body (vehicle body), 12... Rear body, 13... Lift angle sensor, 14... Bell crank angle sensor, 25... Lift pressure sensor, 26... Bucket pressure sensor, 31... Control device, 32... Load calculation device, 33... Pre-loading load calculation unit, 34... During-loading load calculation unit, 35... Cylinder thrust calculation unit during no-load, 36... Load correction unit

Claims

1. A lift arm pivotally connected to the vehicle body, A lift cylinder that performs a lift-up operation of pivoting the lift arm upward and a lift-down operation of pivoting the lift arm downward, A bucket pivotally connected to the lift arm, A bucket cylinder that performs a tilt operation of pivoting the bucket upward and a dump operation of pivoting the bucket downward, A lift pressure sensor that measures the pressure of the lift cylinder, A bucket pressure sensor that measures the pressure of the bucket cylinder, A load calculation device that calculates the thrust of the lift cylinder and the thrust of the bucket cylinder from the measured values of the lift pressure sensor and the bucket pressure sensor respectively, and calculates the loading load of the bucket based on the calculated thrust of the lift cylinder and the thrust of the bucket cylinder. The load calculation device, in a loaded state where a load is loaded on the bucket, maintains a full-tilt posture with the opening of the bucket facing upward, and is in the middle of performing the dump operation and the lift-up operation on the bucket located at a predetermined loading start height. From the thrust of the lift cylinder and the thrust of the bucket cylinder during the loading operation, when the bucket is in an empty load state, maintaining the full-tilt posture, and performing the dump operation and the lift-up operation on the bucket located at the loading start height, based on the difference value obtained by subtracting the thrust of the lift cylinder and the thrust of the bucket cylinder respectively, calculates the loading load during the loading operation. A wheel loader characterized by the above.

2. A bell crank that connects the bucket and the bucket cylinder and transmits the thrust of the bucket cylinder to the bucket, A lift angle sensor that measures the lift angle formed by the lift arm with respect to the vehicle body, further comprising a bell crank angle sensor that measures a bell crank angle formed by the bell crank with respect to the lift arm. The load calculation device With the bucket in the empty load state, maintaining the fully tilted posture, when performing the dump operation and the lift-up operation on the bucket positioned at the loading start height, calculates and stores the thrust of the lift cylinder and the thrust of the bucket cylinder respectively according to the lift angle and the bell crank angle that change, an empty load cylinder thrust calculation unit; calculates the thrust of the lift cylinder and the thrust of the bucket cylinder respectively according to the lift angle and the bell crank angle that change during the loading operation, and subtracts the thrust of the lift cylinder and the thrust of the bucket cylinder stored in the empty load cylinder thrust calculation unit from the calculated thrust of the lift cylinder and the thrust of the bucket cylinder respectively to calculate the difference value, and calculates the loaded load during the loading operation based on the calculated difference value, a loading in-process load calculation unit. The wheel loader according to claim 1, characterized in that.

3. The load calculation device With the bucket in the loaded state, maintaining the fully tilted posture, calculates the thrust of the lift cylinder in the state before the start of the loading operation which is a state of being stationary at the loading start height, and based on the difference value obtained by subtracting the thrust of the lift cylinder stored in the empty load cylinder thrust calculation unit from the calculated thrust of the lift cylinder, calculates the loaded load in the state before the start of the loading operation, a pre-loading load calculation unit; further comprising a load correction unit that corrects the loaded load during the loading operation based on the loaded load in the state before the start of the loading operation. The wheel loader according to claim 2, characterized in that.

4. The loading-in-process load calculation unit calculates the load during loading in a state where the bucket is in the loaded state, maintaining the fully tilted posture and starting the dump operation and the lift operation with respect to the bucket positioned at the loading start height, and before the load is discharged from the bucket, i.e., immediately after the start of the loading operation. The load correction unit corrects the load during the loading operation based on the ratio between the load during loading before the start of the loading operation and the load during loading immediately after the start of the loading operation. The wheel loader according to claim 3, characterized in that.

5. During the dump operation on the bucket in the unloaded state, the no-load cylinder thrust calculation unit acquires the measured values of the lift pressure sensor and the bucket pressure sensor, calculates and stores the thrust of the lift cylinder and the thrust of the bucket cylinder from the acquired measured values. The wheel loader according to claim 3, characterized in that.

6. The wheel loader further includes a control device for controlling the operations of the lift cylinder and the bucket cylinder. When the load during the loading operation reaches the target load indicating the load of the load remaining in the bucket at the end of the loading operation, the control device stops the dump operation and performs the tilt operation. After the tilt operation is performed, the control device performs the dump operation to rotate the bucket at an angle smaller than the angle by which the bucket rotates in the tilt operation and at which the load in the bucket is not discharged, and ends the loading operation by stopping the dump operation and the lift operation. The loading-in-process load calculation unit calculates the load during loading in a state where the bucket is rotated at an angle at which the load is not discharged, which is performed immediately before the end of the loading operation, during the dump operation, or in a state where the dump operation and the lift operation are stopped, i.e., at the end of the loading operation. The wheel loader according to claim 5, characterized in that.

7. The control device controls the speed of the lifting operation during the loading operation to a constant speed such that the stroke of the lift cylinder at the start of the loading operation monotonically increases to a stroke equal to or less than the maximum stroke of the lift cylinder at the end of the loading operation. The wheel loader according to claim 6, characterized in that.

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