WORK MACHINE AND METHOD FOR CONTROLLING WORK MACHINE

Abstract

A work machine includes a vehicle body, a lift frame supported so as to be rotatable about a lift axis with respect to the vehicle body, a blade supported so as to be rotatable about a pitch axis with respect to the lift frame, a pitch actuator connected to the blade and the lift frame, and a controller. The pitch actuator is configured to cause the blade to perform a pitch motion about the pitch axis in a forward tilt direction and a backward tilt direction. The controller is configured to acquire a traction force of the vehicle body and control the pitch actuator so as to change a pitch angle of the blade based on the traction force.

Description

BACKGROUND

Field of the Invention

The present invention relates to a work machine and a method for controlling a work machine.

Background Information

In some work machines, a pitch angle of a blade can be adjusted according to an operation by an operator. For example, a work machine in Japanese Unexamined Patent Publication No. H07-252859 is provided with an operating lever for adjusting the pitch angle of the blade. The operating lever is provided with a switch. Upon the operating lever being tilted to the right with the switch on, a hydraulic cylinder is controlled so that the blade is tilted forward (pitch dump). Upon the operating lever being tilted to the left with the switch on, the hydraulic cylinder is controlled so that the blade is tilted backward (pitch back).

SUMMARY

The pitch angle of the blade affects the work efficiency in digging work, leveling work, or the like. An appropriate pitch angle of the blade differs depending on the type of work. For example, when the pitch angle is small, that is, when the blade is tilted backward, the digging resistance is small and the digging performance is desirable, but the amount of soil that spills backward is large and the leveling performance is low. Conversely, when the pitch angle is large, that is, when the blade is tilted forward, the penetration force of the blade in the downward direction is large and the leveling performance is desirable, but the digging resistance is large and the digging performance is low.

In a case where the digging resistance is large during the work such as digging in which the traction force of the work machine is large, the ground contact pressure in the front-back direction of the work machine becomes unbalanced, and thus it is likely to result in an occurrence of slip. The balance of the ground contact pressure can be improved by adjusting the pitch angle of the blade. For instance, reducing the pitch angle increases the amount of soil held by the blade. As a result, similarly to a case where a counterweight is attached to the front portion of the vehicle body, the force that lifts the front portions of crawler belts is reduced, whereby the balance of the ground contact pressure is improved. However, it is not easy for even a skilled operator to manually select an appropriate pitch angle in order to suppress an occurrence of slip. An object of the present disclosure is to make it possible to easily and appropriately adjust a pitch angle of the blade in a work machine in order to suppress the occurrence of slip.

A work machine according to a first aspect of the present disclosure is a work machine including a vehicle body, a lift frame, a blade, a pitch actuator, and a controller. The lift frame is supported so as to be rotatable about a lift axis with respect to the vehicle body. The blade is supported so as to be rotatable about a pitch axis with respect to the lift frame. The pitch actuator is connected to the blade and the lift frame and causes the blade to perform a pitch motion about the pitch axis in a forward tilt direction and a backward tilt direction. The controller acquires a traction force of the vehicle body. The controller controls the pitch actuator so as to change a pitch angle of the blade based on the traction force.

A method according to a second aspect of the present disclosure is a method for controlling a work machine. The work machine includes a vehicle body, a lift frame, a blade, and a pitch actuator. The lift frame is supported so as to be rotatable about a lift axis with respect to the vehicle body. The blade is supported so as to be rotatable about a pitch axis with respect to the lift frame. The pitch actuator is connected to the blade and the lift frame and causes the blade to perform a pitch motion about the pitch axis in a forward tilt direction and a backward tilt direction. The method includes acquiring a traction force of the vehicle body and controlling the pitch actuator so as to change a pitch angle of the blade based on the traction force.

According to the present disclosure, the pitch actuator is controlled so that the pitch angle of the blade is changed based on the traction force of the work machine. As a result, the balance of the ground contact pressure in the front-back direction of the work machine is improved, thereby suppressing the occurrence of slip. Therefore, according to the present disclosure, it is possible to easily and appropriately adjust the pitch angle of the blade in the work machine in order to suppress the occurrence of slip.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of a work machine according to an embodiment.

FIG. 2 is a block diagram illustrating a configuration of a drive system and a control system of the work machine.

FIG. 3 is a schematic view illustrating a lift motion of a blade.

FIG. 4A, FIG. 4B and FIG. 4C are views illustrating pitch angles of the blade.

FIG. 5 is a schematic view illustrating ground contact pressure of crawler belts of the work machine.

FIG. 6 is a schematic view illustrating a control of a pitch angle in an automatic mode.

FIG. 7 is a graph illustrating an example of pitch angle data.

DETAILED DESCRIPTION OF EMBODIMENT(S)

A work machine according to an embodiment will be described below with reference to the drawings. FIG. 1 is a side view of a work machine 1 according to the embodiment. The work machine 1 according to the present embodiment is a bulldozer. The work machine 1 includes a vehicle body 11 and a work implement 12.

The vehicle body 11 includes an operating cabin 13, an engine compartment 14, and a travel device 15. An operator's seat that is not illustrated is disposed in the operating cabin 13. The engine compartment 14 is disposed in front of the operating cabin 13. The travel device 15 is provided at a lower portion of the vehicle body 11. The travel device 15 includes front wheels 41, rear wheels 42, and crawler belts 16. Only the left crawler belt 16 is illustrated in FIG. 1. The front wheels 41 are disposed in front of the rear wheels 42. The crawler belts 16 are wound around the front wheels 41 and the rear wheels 42. The work machine 1 travels due to the rotation of the crawler belts 16.

The work implement 12 is attached to the vehicle body 11. The work implement 12 includes a lift frame 17, a blade 18, a lift actuator 19, and a pitch actuator 20. The lift frame 17 is supported so as to be rotatable about a lift axis X1 with respect to the vehicle body 11. The lift axis X1 extends in a lateral direction of the vehicle body 11. The lift frame 17 rotates about the lift axis X1, thereby performing a lift motion up and down.

The blade 18 is disposed in front of the vehicle body 11. The blade 18 is supported so as to be rotatable about a pitch axis X2 with respect to the lift frame 17. The pitch axis X2 extends in the lateral direction of the vehicle body 11. The blade 18 rotates about the pitch axis X2, thereby performing a pitch motion in a forward tilt direction and a backward tilt direction. The blade 18 moves up and down as the lift frame 17 moves up and down.

The lift actuator 19 is coupled to the vehicle body 11 and the lift frame 17. The lift actuator 19 is a hydraulic cylinder. Due to the extension and contraction of the lift actuator 19, the lift frame 17 performs the lift motion up and down. The lift actuator 19 contracts, thereby causing the blade 18 to be raised. The lift actuator extends, thereby causing the blade 18 to be lowered.

The pitch actuator 20 is coupled to the lift frame 17 and the blade 18. The pitch actuator 20 is a hydraulic cylinder. Due to the extension and contraction of the pitch actuator 20, the blade 18 performs the pitch motion forward and backward. A portion of the blade 18, for example, its upper end moves forward and backward, thereby causing the blade 18 to perform the pitch motion about the pitch axis X2. The pitch actuator 20 extends, thereby causing the blade 18 to be tilted forward. The pitch actuator 20 contracts, thereby causing the blade 18 to be tilted backward.

FIG. 2 is a block diagram illustrating a configuration of a drive system 2 and a control system 3 of the work machine 1. As illustrated in FIG. 2, the drive system 2 includes an engine 22, a hydraulic pump 23 and a power transmission device 24. The hydraulic pump 23 is driven by the engine 22 to discharge hydraulic fluid. The hydraulic fluid discharged from the hydraulic pump 23 is supplied to the lift actuator 19 and the pitch actuator 20. Although one hydraulic pump is illustrated in FIG. 2, a plurality of hydraulic pumps may be provided.

The power transmission device 24 transmits driving force of the engine 22 to the travel device 15. The power transmission device 24 may be a hydro static transmission (HST), for example. Alternatively, the power transmission device 24 may be, for example, a transmission having a torque converter or a plurality of transmission gears.

The control system 3 includes a controller 26 and a control valve 27. The controller 26 is programmed to control the work machine 1 based on acquired data. The controller 26 includes a storage device 28 and a processor 29. The processor 29 includes a CPU, for example. The storage device 28 includes a memory and an auxiliary storage device, for example. The storage device 28 may be a RAM or a ROM, for example. The storage device 28 may be a semiconductor memory, a hard disk, or the like. The storage device 28 is an example of a non-transitory computer-readable recording medium. The storage device 28 stores computer instructions that are executable by the processor 29 and for controlling the work machine 1.

The control valve 27 is a proportional control valve and is controlled by a command signal from the controller 26. The control valve 27 is disposed between the hydraulic pump 23 and a hydraulic actuator such as the lift actuator 19 and the pitch actuator 20. The control valve 27 controls the flow rate of the hydraulic fluid supplied from the hydraulic pump 23 to the lift actuator 19. The control valve 27 controls the flow rate of the hydraulic fluid supplied from the hydraulic pump 23 to the pitch actuator 20. The control valve 27 may be a pressure proportional control valve. Alternatively, the control valve 27 may be an electromagnetic proportional control valve.

The control system 3 includes an operating device 31 and an input device 32. The operating device 31 includes a lever, for example. Alternatively, the operating device 31 may include a pedal or a switch. An operator can manually operate the travel of the work machine 1 and the motion of the work implement 12 using the operating device 31. The operating device 31 outputs an operation signal indicative of an operation of the operating device 31. The controller 26 receives the operation signal from the operating device 31.

The operating device 31 is configured to operate the lift motion of the blade 18. Specifically, the operating device 31 is configured to operate a raising operation and a lowering operation of the blade 18. When the operator performs the raising operation on the operating device 31, the controller 26 controls the lift actuator 19 so that the blade 18 is raised. When the operator performs the lowering operation on the operating device 31, the controller 26 controls the lift actuator 19 so that the blade 18 is lowered.

FIG. 3 is a schematic view illustrating the lift motion of the work machine 1. In FIG. 3, P1 indicates the highest position of a blade tip P0 of the blade 18. P2 indicates the lowest position of the blade tip P0 of the blade 18. The work machine 1 can cause the blade 18 to perform the lift motion between the highest position P1 and the lowest position P2.

The operating device 31 is configured to operate the pitch motion of the blade 18. Specifically, the operating device 31 is configured to operate a forward tilt operation and a backward tilt operation of the blade 18. When the operator performs the forward tilt operation on the operating device 31, the controller 26 controls the pitch actuator 20 so that the blade 18 is tilted forward. When the operator performs the backward tilt operation on the operating device 31, the controller 26 controls the pitch actuator 20 so that the blade 18 is tilted backward.

FIGS. 4A to 4C are views illustrating pitch angles of the blade 18. As illustrated in FIGS. 4A to 4C, pitch angles θ1 to θ3 of the blade 18 are the angles between the blade tip P0 of the blade 18 and a ground contact surface G1 of the crawler belts 16. FIG. 4B illustrates a pitch angle θ2 of the blade 18 in a normal state. FIG. 4A illustrates a pitch angle θ1 of the blade 18 tilted forward in comparison with the normal state. FIG. 4C illustrates a pitch angle θ3 of the blade 18 tilted backward in comparison with the normal state. The pitch angle increases as the blade 18 is tilted forward. The pitch angle decreases as the blade 18 is tilted backward. That is, the following formula θ1>θ2>θ3 is satisfied.

The operating device 31 may be a hydraulic pilot type device. For example, the operating device 31 may output pilot hydraulic pressure according to the operation of the operating device 31. The control valve 27 is controlled by the pilot hydraulic pressure from the operating device 31, whereby the lift actuator 19 or the pitch actuator 20 may be controlled. The controller 26 may receive a signal indicative of the pilot hydraulic pressure as the operation signal.

The input device 32 includes a touch screen, for example. The input device 32 may include another device such as a switch. The operator can set a control mode of the pitch angle of the blade 18 by the controller 26 using the operating device 31. The control mode of the pitch angle of the blade 18 will be described later in detail.

As illustrated in FIG. 2, the control system 3 includes a vehicle body sensor 34, a frame sensor 35, and a blade sensor 36. The vehicle body sensor 34 is attached to the vehicle body 11. The vehicle body sensor 34 detects a posture of the vehicle body 11. The frame sensor 35 is attached to the lift frame 17. The frame sensor 35 detects a posture of the lift frame 17. The blade sensor 36 is attached to the blade 18. The blade sensor 36 detects a posture of the blade 18.

The vehicle body sensor 34, the frame sensor 35, and the blade sensor 36 are inertial measurement units (IMU). However, the frame sensor 35 and the blade sensor 36 are not limited to the IMU and may be another sensor such as an angle sensor, a cylinder stroke sensor, or the like.

The vehicle body sensor 34 detects an angle in the front-back direction of the vehicle body 11 with respect to the horizontal direction (vehicle pitch angle). The frame sensor 35 detects a rotation angle of the lift frame 17. The blade sensor 36 detects the pitch angle of the blade 18. The vehicle body sensor 34, the frame sensor 35, and the blade sensor 36 output detection signals indicative of the angles detected by the respective sensors.

The control system 3 includes a traction force sensor 37. The traction force sensor 37 detects a traction force of the work machine 1. For example, in a case where the power transmission device 24 is an HST, the traction force sensor 37 is a hydraulic sensor that detects the driving hydraulic pressure of the hydraulic motor of the HST. The controller 26 calculates the traction force of the work machine 1 from the driving hydraulic pressure. Alternatively, in a case where the power transmission device 24 includes a torque converter, the traction force sensor 37 may detect an input rotation speed and an output rotation speed of the torque converter. The controller 26 may calculate the traction force of the work machine 1 from a rotation speed ratio and a torque ratio between the input and output of the torque converter. Alternatively, the controller 26 may calculate the traction force of the work machine 1 from an output torque of the engine 22.

Next, the control mode of the pitch angle of the blade 18 will be explained. The control mode of the pitch angle of the blade 18 includes an automatic mode and a manual mode. The controller 26 switches between the automatic mode and the manual mode according to the operation of the input device 32. The operator can select the automatic mode or the manual mode by operating the input device 32.

In the automatic mode, the controller 26 controls the pitch actuator 20 so as to change the pitch angle of blade 18 based on the traction force of the work machine 1. The controller 26 executes the control of the pitch angle in the automatic mode when a predetermined execution condition is satisfied. The predetermined execution condition includes a first condition and a second condition.

The first condition is that the traction force is greater than or equal to a first threshold. The first threshold is determined based on the magnitude of the traction force when a shoe slip occurs. FIG. 5 is a schematic view illustrating the ground contact pressure of the crawler belts 16 of the work machine 1. In FIG. 5, arrows A1 indicate the ground contact pressure of the crawler belts 16. A arrow F1 indicates the traction force of the work machine 1. When the traction force F1 is greater than or equal to the first threshold, the ground contact pressure A1 is not constant but uneven in the front-back direction of the work machine 1 as illustrated in FIG. 5. In such a state, a shoe slip is likely to occur.

The second condition is that the work machine 1 is not traveling uphill. The controller 26 determines whether the work machine 1 is traveling uphill based on the pitch angle of the vehicle body 11 detected by the vehicle body sensor 34, for example. The controller 26 executes the control of the pitch angle in the automatic mode when the first condition and the second condition are satisfied. The controller 26 does not execute the control of the pitch angle in the automatic mode when either the first condition or the second condition is not satisfied. Therefore, when the controller 26 determines that the work machine 1 is traveling uphill, the controller does not execute the control of the pitch angle in the automatic mode. In the automatic mode, the controller 26 controls the pitch actuator 20 so that the blade 18 is tilted backward as illustrated in FIG. 6. As a result, the ground contact pressure A1 becomes close to being uniform in the front-back direction of the work machine 1 due to the counterweight effect, thereby suppressing the occurrence of shoe slip.

The controller 26 stores pitch angle data. The pitch angle data defines the relation between the traction force F1 and a target pitch angle. The controller 26 refers to the pitch angle data to determine the target pitch angle from the traction force F1. The controller 26 controls the pitch actuator 20 so that the pitch angle of the blade 18 is the target pitch angle.

FIG. 7 is a graph illustrating an example of pitch angle data. In FIG. 7, B1 is the above-mentioned first threshold. B2 is a second threshold and is greater than the first threshold B1. The pitch angle data defines the target pitch angle that decreases according to an increase of the traction force F1 in a range from the first threshold B1 to the second threshold B2 of the traction force F1. Therefore, the controller 26 causes the blade 18 to be tilted backward according to the increase of the traction force F1 in the range from the first threshold B1 to the second threshold B2 under the automatic control. The pitch angle data defines the target pitch angle that is constant at a minimum pitch angle θmin with respect to the traction force F1 greater than or equal to the second threshold B2. The minimum pitch angle θmin is a limit value of the pitch angle of the blade 18 in the backward tilt direction. Therefore, the controller 26 causes the blade 18 to be tilted backward to a limit position in the backward tilt direction when the traction force F1 is greater than or equal to the second threshold B2.

In the manual mode, the controller 26 controls the pitch actuator 20 so as to change the pitch angle of the blade 18 according to the operation of the operating device 31. Also, when the operation device 31 is not operated, the controller 26 controls the pitch actuator 20 so as to maintain the pitch angle of the blade 18. For example, when the operation device 31 is not operated, the controller 26 controls the pitch actuator 20 so as to maintain the pitch angle of the blade 18 even if there is a leakage of the hydraulic fluid at the control valve 27.

In the work machine 1 according to the present embodiment described above, the pitch actuator 20 is controlled so as to change the pitch angle of the blade 18 based on the traction force F1 of the work machine 1. As a result, the balance of the ground contact pressure A1 in the front-back direction of the work machine 1 is improved, thereby suppressing the occurrence of shoe slip.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned embodiment and various modifications can be made without departing from the gist of the invention.

The work machine 1 is not limited to a bulldozer and may be another vehicle such as a wheel loader, a motor grader, or the like. The controller 26 may have a plurality of controllers separate from each other. The processes by the controller 26 are not limited to those of the above-mentioned embodiment and may be changed. A portion of the processes in the automatic mode or the manual mode described above may be omitted. Alternatively, a portion of the processes described above may be changed.

The lift actuator 19 and the pitch actuator 20 are not limited to hydraulic cylinders. The lift actuator 19 and the pitch actuator 20 may be another actuator such as an electric motor, for example.

According to the present disclosure, it is possible to easily and appropriately adjust the pitch angle of the blade in the work machine in order to suppress an occurrence of slip.

Claims

1. A work machine comprising: a vehicle body;a lift frame supported so as to be rotatable about a lift axis with respect to the vehicle body;a blade supported so as to be rotatable about a pitch axis with respect to the lift frame;a pitch actuator connected to the blade and the lift frame, the pitch actuator being configured to cause the blade to perform a pitch motion about the pitch axis in a forward tilt direction and a backward tilt direction; anda controller configured to acquire a traction force of the vehicle body andcontrol the pitch actuator so as to change a pitch angle of the blade based on the traction force.

2. The work machine according to claim 1, wherein the controller is configured to determine whether the traction force is greater than or equal to a first threshold, andcontrol the pitch actuator so that the blade is tilted backward upon determining that the traction force is greater than or equal to the first threshold.

3. The work machine according to claim 2, wherein the controller is configured to control the pitch actuator so that the blade is tilted backward as the traction force increases.

4. The work machine according to claim 2, wherein the controller is configured to determine whether the traction force is greater than or equal to a second threshold that is greater than the first threshold, andcontrol the pitch actuator so that the blade is tilted backward to a limit position in the backward tilt direction when the traction force is greater than or equal to the second threshold.

5. The work machine according to claim 1, wherein the controller is configured to determine whether the work machine is traveling uphill, andcontrol the pitch actuator so as to change the pitch angle of the blade based on the traction force upon determining that the work machine is not traveling uphill.

6. A method for controlling a work machine including a vehicle body, a lift frame supported so as to be rotatable about a lift axis with respect to the vehicle body, a blade supported so as to be rotatable about a pitch axis with respect to the lift frame, and a pitch actuator connected to the blade and the lift frame, the pitch actuator being configured to cause the blade to perform a pitch motion about the pitch axis in a forward tilt direction and a backward tilt direction, the method for controlling the work machine comprising: acquiring a traction force of the vehicle body; andcontrolling the pitch actuator so as to change a pitch angle of the blade based on the traction force.

7. The method according to claim 6, further comprising: determining whether the traction force is greater than or equal to a first threshold; andcontrolling the pitch actuator so that the blade is tilted backward upon determining that the traction force is greater than or equal to the first threshold.

8. The method according to claim 7, further comprising: controlling the pitch actuator so that the blade is tilted backward as the traction force increases.

9. The method according to claim 7, further comprising: determining whether the traction force is greater than or equal to a second threshold that is greater than the first threshold; andcontrolling the pitch actuator so that the blade is tilted backward to a limit position in the backward tilt direction when the traction force is greater than or equal to the second threshold.

10. The method according to claim 6, further comprising: determining whether the work machine is traveling uphill; andcontrolling the pitch actuator so as to change the pitch angle of the blade based on the traction force upon determining that the work machine is not traveling uphill.