WORK MACHINE, METHOD OF AND SYSTEM FOR CONTROLLING WORK MACHINE

Abstract

A work machine includes a vehicle body, a work implement including a blade, a plurality of actuators connected to the work implement, an operating device operable to change the posture of the blade, a sensor that detects a current posture of the blade, and a controller. The work implement is movably connected to the vehicle body. The plurality of actuators change a posture of the blade with respect to the vehicle body. The controller obtains the current posture of the blade. The controller determines target stroke lengths for the actuators, respectively, such that the blade is moved in a blade normal line direction from the current posture by a combination of stroke motions of the actuators depending on an operation to the operating device. The blade normal line direction is perpendicular to a lengthwise direction of the blade. The controller controls the actuators based on the target stroke lengths.

Claims

1. A work machine comprising: a vehicle body; a work implement including a blade, the work implement being movably connected to the vehicle body; a plurality of actuators connected to the work implement, the plurality of actuators being configured to change a posture of the blade with respect to the vehicle body; an operating device operable to change the posture of the blade; a sensor configured to detect a current posture of the blade; and a controller configured to obtain the current posture of the blade, determine target stroke lengths for the plurality of actuators, respectively, such that the blade is moved in a blade normal line direction from the current posture by a combination of stroke motions of the plurality of actuators depending on an operation to the operating device, the blade normal line direction being perpendicular to a lengthwise direction of the blade, and control the plurality of actuators based on the target stroke lengths.

2. The work machine according to claim 1, wherein the controller is configured to select one from at least a first mode and a second mode as a control mode for the blade depending on the operation to the operating device, control the plurality of actuators in the first mode such that the blade is moved in a vertical direction depending on the operation to the operating device, the vertical direction being parallel to a gravitational direction, and control the plurality of actuators in the second mode such that the blade is moved in the blade normal line direction depending on the operation to the operating device.

3. The work machine according to claim 2, wherein the controller is configured to select one from at least the first mode and the second mode depending on the current posture of the blade as the control mode for the blade depending on the operation to the operating device.

4. The work machine according to claim 3, wherein the controller is configured to determine which of a normal posture and a bank cutting posture is taken by the blade as the current posture, the blade having a roll angle larger when taking the bank cutting posture than when taking the normal posture, select the first mode as the control mode for the blade when the current posture of the blade is the normal posture, and select the second mode as the control mode for the blade when the current posture of the blade is the bank cutting posture.

5. The work machine according to claim 4, wherein the sensor is configured to detect the roll angle of the blade with respect to either a ground or the vehicle body, and the controller is configured to determine which of the normal posture and the bank cutting posture is taken by the blade based on the roll angle.

6. The work machine according to claim 4, wherein the vehicle body includes a front frame extending in a back-and-forth direction of the vehicle body, the work implement includes a lifter bracket rotatably connected to the front frame, the blade is supported by the front frame through the lifter bracket, the sensor is configured to detect a rotational angle of the lifter bracket with respect to the front frame, and the controller is configured to determine which of the normal posture and the bank cutting posture is taken by the blade based on the rotational angle of the lifter bracket.

7. The work machine according to claim 2, wherein the operating device includes a left lift operating member, and the controller is configured to control the plurality of actuators in the first mode such that a left end of the blade is moved in the vertical direction depending on the operation to the left lift operating member, and control the plurality of actuators in the second mode such that the left end of the blade is moved in the blade normal line direction depending on the operation to the left lift operating member.

8. The work machine according to claim 2, wherein the operating device includes a right lift operating member, and the controller is configured to control the plurality of actuators in the first mode such that a right end of the blade is moved in the vertical direction depending on the operation to the right lift operating member, and control the plurality of actuators in the second mode such that the right end of the blade is moved in the blade normal line direction depending on the operation to the right lift operating member.

9. A method of controlling a work machine, the work machine including a vehicle body, a work implement, and a plurality of actuators, the work implement including a blade, the work implement being movably connected to the vehicle body, the plurality of actuators being connected to the work implement, the plurality of actuators being configured to change a posture of the blade with respect to the vehicle body, the method comprising: obtaining a current posture of the blade; obtaining a signal indicating an operation to the operating device; determining target stroke lengths for the plurality of actuators, respectively, such that the blade is moved in a blade normal line direction from the current posture by a combination of stroke motions of the plurality of actuators depending on the operation to the operating device, the blade normal line direction being perpendicular to a lengthwise direction of the blade; and controlling the plurality of actuators based on the target stroke lengths.

10. The method according to claim 9, further comprising: selecting one from at least a first mode and a second mode as a control mode for the blade depending on the operation to the operating device; controlling the plurality of actuators in the first mode such that the blade is moved in a vertical direction depending on the operation to the operating device, the vertical direction being parallel to a gravitational direction; and controlling the plurality of actuators in the second mode such that the blade is moved in the blade normal line direction depending on the operation to the operating device.

11. The method according to claim 10, further comprising: selecting one from at least the first mode and the second mode depending on the current posture of the blade as the control mode for the blade depending on the operation to the operating device.

12. The method according to claim 11, further comprising: determining which of a normal posture and a bank cutting posture is taken by the blade as the current posture, the blade having a roll angle larger when taking the bank cutting posture than when taking the normal posture; selecting the first mode as the control mode for the blade when the current posture of the blade is the normal posture; and selecting the second mode as the control mode for the blade when the current posture of the blade is the bank cutting posture.

13. The method according to claim 12, further comprising: detecting the roll angle of the blade with respect to either a ground or the vehicle body; and determining which of the normal posture and the bank cutting posture is taken by the blade based on the roll angle.

14. The method according to claim 12, wherein the vehicle body includes a front frame extending in a back-and-forth direction of the vehicle body, the work implement includes a lifter bracket rotatably connected to the front frame, the blade is supported by the front frame through the lifter bracket, and the method further comprises: detecting a rotational angle of the lifter bracket with respect to the front frame; and determining which of the normal posture and the bank cutting posture is taken by the blade based on the rotational angle of the lifter bracket.

15. The method according to claim 10, wherein the operating device includes a left lift operating member, and the method further comprises: controlling the plurality of actuators in the first mode such that a left end of the blade is moved in the vertical direction depending on the operation to the left lift operating member; and controlling the plurality of actuators in the second mode such that the left end of the blade is moved in the blade normal line direction depending on the operation to the left lift operating member.

16. The method according to claim 10, wherein the operating device includes a right lift operating member, and the method further comprises: controlling the plurality of actuators in the first mode such that a right end of the blade is moved in the vertical direction depending on the operation to the right lift operating member; and controlling the plurality of actuators in the second mode such that the right end of the blade is moved in the blade normal line direction depending on the operation to the right lift operating member.

17. A system for controlling a work machine, the work machine including a vehicle body, a work implement, and a plurality of actuators, the work implement including a blade, the work implement being movably connected to the vehicle body, the plurality of actuators being connected to the work implement, the plurality of actuators being configured to change a posture of the blade with respect to the vehicle body, the system comprising: an operating device being operable to change the posture of the blade; and a controller configured to obtain a current posture of the blade, determine target stroke lengths for the plurality of actuators, respectively, such that the blade is moved in a blade normal line direction from the current posture by a combination of stroke motions of the plurality of actuators depending on an operation to the operating device, the blade normal line direction being perpendicular to a lengthwise direction of the blade, and control the plurality of actuators based on the target stroke lengths.

18. The system according to claim 17, wherein the controller is configured to select one from at least a first mode and a second mode as a control mode for the blade depending on the operation to the operating device, control the plurality of actuators in the first mode such that the blade is moved in a vertical direction depending on the operation to the operating device, the vertical direction being parallel to a gravitational direction, and control the plurality of actuators in the second mode such that the blade is moved in the blade normal line direction depending on the operation to the operating device.

19. The system according to claim 18, wherein the controller is configured to select one from at least the first mode and the second mode depending on the current posture of the blade as the control mode for the blade depending on the operation to the operating device.

20. The system according to claim 19, wherein the controller is configured to determine which of a normal posture and a bank cutting posture is taken by the blade as the current posture, the blade having a roll angle larger when taking the bank cutting posture than when taking the normal posture, select the first mode as the control mode for the blade when the current posture of the blade is the normal posture, and select the second mode as the control mode for the blade when the current posture of the blade is the bank cutting posture.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0013] FIG. 1 is a side view of a work machine according to an embodiment.

[0014] FIG. 2 is a perspective view of a front portion of the work machine.

[0015] FIG. 3 is an exploded perspective view of a configuration regarding a lifter bracket and the periphery thereof.

[0016] FIG. 4 is a schematic view of a drive train and a control system in the work machine.

[0017] FIG. 5 is a schematic rear view of the work machine and shows a posture of a work implement.

[0018] FIG. 6 is a schematic plan view of the work machine and shows the posture of the work implement.

[0019] FIG. 7 is a schematic side view of the work machine and shows the posture of the work implement.

[0020] FIG. 8 is a schematic plan view of the work machine and shows the posture of the work implement.

[0021] FIG. 9 is a schematic plan view of the work machine and shows the posture of the work implement.

[0022] FIG. 10 is a table representing correspondences between operating members operated by an operator and actuators driven by operating the operating members.

[0023] FIG. 11 is a rear view of a mathematical model showing the posture of the work implement.

[0024] FIG. 12 is a rear view of the mathematical model showing the posture of the work implement.

[0025] FIG. 13 is a rear view of the mathematical model showing the posture of the work implement.

[0026] FIG. 14 is a flowchart showing a series of processing of an integrated control for changing the posture of the work implement.

[0027] FIG. 15A and FIG. 15B are rear views of the mathematical model showing the postures of the work implement.

[0028] FIG. 16A, FIG. 16B and FIG. 16C are side views of the mathematical model showing the postures of the work implement.

[0029] FIG. 17A, FIG. 17B and FIG. 17C are side views of the mathematical model showing the postures of the work implement.

[0030] FIG. 18 is a front view of the work implement when a blade is in a normal posture.

[0031] FIG. 19 is a front view of the work implement when the blade is in a bank cutting posture.

[0032] FIG. 20 is a flowchart showing a series of processing of the integrated control.

[0033] FIG. 21 is a schematic view of the drive train and the control system in a work machine according to a modification.

[0034] FIG. 22 is a front view of the work implement when the blade is in the bank cutting posture.

DETAILED DESCRIPTION OF EMBODIMENT(S)

[0035] An embodiment of the present invention will be hereinafter explained with reference to drawings. FIG. 1 is a side view of a work machine 1 according to the embodiment. FIG. 2 is a perspective view of a front portion of the work machine 1. As shown in FIG. 1, the work machine 1 includes a vehicle body 2, front wheels 3, rear wheels 4, and a work implement 5. The vehicle body 2 includes a front frame 11, a rear frame 12, a cab 13, and a power chamber 14.

[0036] The rear frame 12 is connected to the front frame 11. Articulation of the front frame 11 with respect to the rear frame 12 is enabled right and left. It should be noted that in the following explanation, front, rear, right, and left directions are defined as meaning front, rear, right, and left directions of the vehicle body 2 oriented at an articulated angle of 0 degrees, i.e., when the front frame 11 and the rear frame 12 are kept straight.

[0037] The cab 13 and the power chamber 14 are disposed on the rear frame 12. An operator seat (not shown in the drawings) is disposed in the cab 13. A drive train (to be described) is disposed in the power chamber 14. The front frame 11 extends forward from the rear frame 12. The front wheels 3 are attached to the front frame 11. The rear wheels 4 are attached to the rear frame 12.

[0038] The work implement 5 is movably connected to the vehicle body 2. The work implement 5 includes a support member 15, a blade 16, and a lifter bracket 29. The support member 15 is movably connected to the vehicle body 2. The support member 15 supports the blade 16. The support member 15 and the blade 16 are supported by the front frame 11 through the lifter bracket 29. The support member 15 includes a drawbar 17 and a circle 18. The drawbar 17 is disposed below the front frame 11.

[0039] As shown in FIG. 2, the drawbar 17 is connected to a pivot support portion 19 of the front frame 11. The pivot support portion 19 is disposed in a front portion of the front frame 11. The drawbar 17 extends rearward from the front portion of the front frame 11. The drawbar 17 is supported to be pivotable with respect to the front frame 11 at least in an up-and-down direction and a right-and-left direction of the vehicle body 2. For example, the pivot support portion 19 includes a ball joint. The drawbar 17 is connected to the front frame 11 through the ball joint, while being turnable.

[0040] The circle 18 is connected to a rear portion of the drawbar 17. The circle 18 is supported to be rotatable with respect to the drawbar 17. The blade 16 is connected to the circle 18. The blade 16 is supported by the drawbar 17 through the circle 18. The blade 16 is supported by the circle 18, while being turnable about a tilt shaft 21. The tilt shaft 21 extends in the right-and-left direction. The blade 16 is supported by the circle 18, while being slidable in the right-and-left direction.

[0041] The work machine 1 includes a plurality of actuators 22 to 27 for changing the posture of the work implement 5. The plural actuators 22 to 27 include a plurality of hydraulic cylinders 22 to 26. The plural hydraulic cylinders 22 to 26 are connected to the work implement 5. The plural hydraulic cylinders 22 to 26 are expanded and contracted by hydraulic pressure. The plural hydraulic cylinders 22 to 26 are expanded and contracted to change the posture of the work implement 5 with respect to the vehicle body 2. In the following explanation, expansion and contraction of the hydraulic cylinders will be referred to as a stroke motion.

[0042] When described in detail, the plural hydraulic cylinders 22 to 26 include a left lift cylinder 22, a right lift cylinder 23, a drawbar shift cylinder 24, a blade tilt cylinder 25, and a blade shift cylinder 26. The left and right lift cylinders 22 and 23 are disposed away from each other in the right-and-left direction. The left lift cylinder 22 is connected to a left portion of the drawbar 17. The right lift cylinder 23 is connected to a right portion of the drawbar 17. The left and right lift cylinders 22 and 23 are connected to be pivotable right and left with respect to the drawbar 17.

[0043] The left and right lift cylinders 22 and 23 are connected to the front frame 11, while being pivotable right and left. When described in detail, the left and right lift cylinders 22 and 23 are connected to the front frame 11 through the lifter bracket 29. The lifter bracket 29 is rotatably connected to the front frame 11. The lifter bracket 29 supports the left and right lift cylinders 22 and 23 such that the left and right lift cylinders 22 and 23 are made pivotable right and left. The drawbar 17 is pivoted up and down about the pivot support portion 19 by the stroke motions of the left and right lift cylinders 22 and 23. Accordingly, the blade 16 is moved up and down.

[0044] The drawbar shift cylinder 24 is connected to the drawbar 17 and the front frame 11. The drawbar shift cylinder 24 is connected to the front frame 11 through the lifter bracket 29. The drawbar shift cylinder 24 is pivotably connected to the front frame 11. The drawbar shift cylinder 24 is pivotably connected to the drawbar 17. The drawbar shift cylinder 24 extends obliquely downward from the front frame 11 toward the drawbar 17. The drawbar shift cylinder 24 extends from one to the other opposite of the right and left lateral sides of the front frame 11. The drawbar 17 is pivoted right and left about the pivot support portion 19 by the stroke motion of the drawbar shift cylinder 24.

[0045] FIG. 3 is an exploded perspective view of a configuration of the lifter bracket 29 and the periphery thereof. As shown in FIG. 3, a lifter guide 30 is fixed to the front frame 11. The lifter guide 30 has an annular shape and is disposed in the surroundings of the front frame 11. The lifter guide 30 is provided with a plurality of lock holes 301. The plural lock holes 301 are disposed to be aligned in the circumferential direction of the lifter guide 30. It should be noted that in FIG. 3, reference sign 301 is assigned to only a part of the plural lock holes 301 without being assigned to the remainder thereof.

[0046] The lifter bracket 29 includes a through hole 291. The through hole 291 is penetrated by the front frame 11. The lifter bracket 29 includes an upper bracket 29a and a lower bracket 29b. Each of the upper and lower brackets 29a and 29b has a semi-annular shape. The upper and lower brackets 29a and 29b are coupled to each other, while the lifter guide 30 is sandwiched therebetween. The left and right lift cylinders 22 and 23 are attached to the upper bracket 29a. The drawbar shift cylinder 24 is attached to the lower bracket 29b.

[0047] As shown in FIG. 2, the lifter bracket 29 includes lock pins 51 and 52. The lock pins 51 and 52 are disposed in opposition to each other on the lifter guide 30. The lock pins 51 and 52 are provided to be movable into and out of the lock holes 301. In a state that the lock pins 51 and 52 are disposed outside the lock holes 301 (hereinafter referred to as an unlocked state), the lifter bracket 29 is made rotatable with respect to the front frame 11. In a state that the lock pins 51 and 52 are disposed inside the lock holes 301 (hereinafter referred to as a locked state), the lifter bracket 29 is made non-rotatable with respect to the front frame 11 and is fixed to the front frame 11. When the left and right lift cylinders 22 and 23 are expanded and contracted in the unlocked state of the lifter bracket 29, the blade 16 is turned about the front frame 11.

[0048] As shown in FIG. 1, the blade tilt cylinder 25 is connected to the circle 18 and the blade 16. The blade 16 is turned about the tilt shaft 21 by the stroke motion of the blade tilt cylinder 25. As shown in FIG. 2, the blade shift cylinder 26 is connected to the circle 18 and the blade 16. The blade 16 is slid right and left with respect to the circle 18 by the stroke motion of the blade shift cylinder 26.

[0049] The plural actuators 22 to 27 include a rotary actuator 27. The rotary actuator 27 is connected to the drawbar 17 and the circle 18. The rotary actuator 27 rotates the circle 18 with respect to the drawbar 17. Accordingly, the blade 16 is revolved about a rotational axis extending in the up-and-down direction.

[0050] FIG. 4 is a schematic view of a drive train 6 and a control system 7 in the work machine 1. As shown in FIG. 4, the work machine 1 includes a drive source 31, a hydraulic pump 32, a power transmission device 33, and a control valve 34. The drive source 31 is, for instance, an internal combustion engine. Alternatively, the drive source 31 may be an electric motor or a hybrid of an internal combustion engine and an electric motor. The hydraulic pump 32 is driven by the drive source 31 to discharges hydraulic fluid.

[0051] The control valve 34 is connected to the hydraulic pump 32 and the plural hydraulic cylinders 22 to 26 through a hydraulic circuit. The control valve 34 includes a plurality of valves connected to the plural hydraulic cylinders 22 to 26, respectively. The control valve 34 controls the flow rate of the hydraulic fluid to be supplied from the hydraulic pump 32 to each of the plural hydraulic cylinders 22 to 26.

[0052] In the present embodiment, the rotary actuator 27 is a hydraulic motor. The control valve 34 is connected to the hydraulic pump 32 and the rotary actuator 27 through the hydraulic circuit. The control valve 34 controls the flow rate of the hydraulic fluid supplied from the hydraulic pump 32 to the rotary actuator 27. It should be noted that the rotary actuator 27 may be an electric motor.

[0053] The power transmission device 33 transmits a drive force generated by the drive source 31 to the rear wheels 4. The power transmission device 33 may include a torque converter and/or a plurality of shifting gears. Alternatively, the power transmission device 33 may be any suitable transmission such as an HST (Hydraulic Static Transmission) or an HMT (Hydraulic Mechanical Transmission).

[0054] As shown in FIG. 4, the work machine 1 includes an operating device 35 and a controller 36. The operating device 35 is operable by an operator to change the posture of the work implement 5. The posture of the work implement 5 is defined by a plurality of parameters. The plural parameters indicate the position and the orientation of the blade 16 with respect to the vehicle body 2. FIG. 5 is a schematic rear view of the work machine 1 and shows the posture of the work implement 5. As shown in FIG. 5, the plural parameters include the height of a left end 161 of the blade 16 and the height of a right end 162 of the blade 16.

[0055] The plural parameters include a yaw angle 1, a pitch angle 2, and a roll angle 3 of the drawbar 17. FIG. 6 is a schematic plan view of the work machine 1 and shows the posture of the work implement 5. As shown in FIG. 6, the yaw angle 1 of the drawbar 17 is a right-and-left directional inclination angle of the drawbar 17 with respect to the back-and-forth direction of the vehicle body 2. It should be noted that the yaw angle 1 of the drawbar 17 may be a right-and-left directional inclination angle of the drawbar 17 with respect to the back-and-forth direction of the front frame 11. The right-and-left directional position of the blade 16 is changed depending on the yaw angle 1 of the drawbar 17.

[0056] FIG. 7 is a schematic side view of the work machine 1 and shows the posture of the work implement 5. As shown in FIG. 7, the pitch angle 2 of the drawbar 17 is an up-and-down directional inclination angle of the drawbar 17 with respect to the back-and-forth direction of the vehicle body 2. As shown in FIG. 5, the roll angle 3 of the drawbar 17 is an inclination angle of the drawbar 17 about a roll axis A1 extending in the back-and-forth direction of the vehicle body 2.

[0057] The plural parameters include a rotational angle 4 of the circle 18, a tilt angle 5 of the blade 16, and a shift amount W1 of the blade 16. FIG. 8 is a schematic plan view of the work machine 1 and shows the posture of the work implement 5. As shown in FIG. 8, the rotational angle 4 of the circle 18 is the rotational angle 4 of the circle 18 with respect to the back-and-forth direction of the vehicle body 2. As shown in FIG. 7, the tilt angle 5 of the blade 16 is an inclination angle of the blade 16 about the tilt shaft 21 extending in the right-and-left direction. FIG. 9 is a schematic plan view of the work machine 1 and shows the posture of the work implement 5. As shown in FIG. 9, the shift amount W1 of the blade 16 is a right-and-left directional slide amount of the blade 16 with respect to the circle 18.

[0058] The operating device 35 is operable by the operator to change the parameters described above. The operating device 35 includes a plurality of operating members 41 to 46. The plural operating members 41 to 46 are provided in correspondence to the height of the left end 161 of the blade 16, the height of the right end 162 of the blade 16, the yaw angle 1 of the drawbar 17, the rotational angle 4 of the circle 18, the tilt angle 5 of the blade 16, and the shift amount W1 of the blade 16, respectively, amongst the plural parameters described above.

[0059] The plural operating members 41 to 46 include a left lift lever 41, a right lift lever 42, a drawbar shift lever 43, a rotational lever 44, a blade tilt lever 45, and a blade shift lever 46. The left lift lever 41 is operated to change the height of the left end 161 of the blade 16. The right lift lever 42 is operated to change the height of the right end 162 of the blade 16.

[0060] The drawbar shift lever 43 is operated to change the yaw angle 1 of the drawbar 17. The rotational lever 44 is operated to change the rotational angle 4 of the circle 18. The blade tilt lever 45 is operated to change the tilt angle 5 of the blade 16. The blade shift lever 46 is operated to change the shift amount W1 of the blade 16. The plural operating members 41 to 46 output signals indicating operations made by the operator for the operating members 41 to 46, respectively.

[0061] Besides, the operating device 35 includes a lifter lock switch 47. The work machine 1 includes a lifter lock actuator 28. The lifter lock switch 47 is operated to switch the lifter bracket 29 between the locked state and the unlocked state. The lifter lock actuator 28 moves the lock pins 51 and 52 into and out of the lock holes 301. The lifter lock actuator 28 is a hydraulic actuator, for instance, and moves the lock pins 51 and 52 into and out of the lock holes 301 by hydraulic pressure. Alternatively, the lifter lock actuator 28 may be an electric actuator. The lifter lock actuator 28 moves the lock pins 51 and 52 into and out of the lock holes 301 in response to operating the lifter lock switch 47.

[0062] The controller 36 controls the drive source 31 and the power transmission device 33 to make the work machine 1 travel. Besides, the controller 36 controls the hydraulic pump 32 and the control valve 34 to make the work implement 5 operate. The controller 36 includes a processor 37 and a storage device 38. The processor 37 is a CPU, for instance, and executes programs for controlling the work machine 1. The storage device 38 includes memories, such as a RAM and a ROM, and an auxiliary storage device, such as an SSD or an HIDD. The storage device 38 stores the programs and data for controlling the work machine 1.

[0063] As shown in FIG. 4, the work machine 1 includes a plurality of sensors S1 to S6 for detecting the posture of the work implement 5. The plural sensors S1 to S6 are, for instance, magnetic sensors. However, the plural sensors S1 to S6 may be another type of sensors such as optical sensors. The plural sensors S1 to S5 detect the stroke lengths of the plural hydraulic cylinders 22 to 26 described above, respectively. The plural sensors S1 to S5 include a left lift sensor S1, a right lift sensor S2, a drawbar shift sensor S3, a blade tilt sensor S4, and a blade shift sensor S5.

[0064] The left lift sensor S1 detects the stroke length of the left lift cylinder 22. The right lift sensor S2 detects the stroke length of the right lift cylinder 23. The drawbar shift sensor S3 detects the stroke length of the drawbar shift cylinder 24. The blade tilt sensor S4 detects the stroke length of the blade tilt cylinder 25. The blade shift sensor S5 detects the stroke length of the blade shift cylinder 26.

[0065] The plural sensors S1 to S6 include a rotational sensor S6. The rotational sensor S6 detects the rotational angle 4 of the circle 18. The plural sensors S1 to S6 output signals indicating the detected stroke lengths and rotational angle 4, respectively.

[0066] The controller 36 obtains the posture of the work implement 5 based on the signals transmitted thereto from the plural sensors S1 to S6. In other words, the controller 36 calculates current values of the plural parameters described above based on the signals transmitted thereto from the plural sensors S1 to S6. As described above, the controller 36 controls the plural actuators 22 to 27 in response to operating the plural operating members 41 to 46 to execute an integrated control for changing the posture of the work implement 5.

[0067] The integrated control will be hereinafter explained in detail. It should be noted that in the following explanation, the posture of the work implement 5 means the posture of the work implement 5 with respect to the front frame 11. Alternatively, the posture of the work implement 5 means the posture of the work implement 5 with respect to the vehicle body 2 at an articulation angle of 0 degrees. Control executed by the controller 36 for changing the posture of the work implement 5 will be hereinafter explained.

[0068] FIG. 10 is a table representing correspondences between operating members to be operated by the operator and actuators to be driven by operating the operating members. In the work machine 1, due to the structure of the work implement 5 described above, the plural parameters, indicating the posture of the work implement 5, are changed depending on the operation of one of the actuators. For example, FIGS. 11 and 12 are rear views of a mathematical model M1 showing the posture of the work implement 5. The mathematical model M1 indicates geometric positional relations amongst the constituent elements of the work implement 5 that are moved in conjunction with actuating one of the actuators. Based on the mathematical model M1, the controller 36 calculates the positions and angles of the drawbar 17, the circle 18, and the blade 16 in correspondence to the stroke lengths of the hydraulic cylinders 22 to 26 and the rotational angle 4 of the rotary actuator 27.

[0069] FIG. 11 shows the work implement 5 in the initial state thereof. FIG. 12 shows the work implement 5 in which the left lift cylinder 22 is contracted from the initial state thereof. In FIG. 12, other than the left lift cylinder 22, the remaining actuators are kept in the initial states thereof. As shown in FIG. 12, when the left lift cylinder 22 is contracted, the left end 161 of the blade 16 is elevated from a position 161 corresponding to the initial state of the blade 16. However, the right end 162 of the blade 16 is lowered from a position 162 corresponding to the initial state of the blade 16. Besides, the blade 16 is moved leftward from a position in the initial state thereof. In other words, not only the height of the left end 161 of the blade 16 but also both the height of the right end 162 of the blade 16 and the yaw angle 1 of the drawbar 17 are changed depending on the stroke motion of the left lift cylinder 22.

[0070] Therefore, when only the left lift cylinder 22 is actuated in response to operating the left lift lever 41, not only the height of the left end 161 of the blade 16 but also both the height of the right end 162 of the blade 16 and the right-and-left directional position of the drawbar 17 are undesirably changed. In view of this, when the left lift lever 41 is being operated, the controller 36 controls the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24 such that, as shown in FIG. 13, the height of the left end 161 of the blade 16 is changed depending on the operation of the left lift lever 41, while the height of the right end 162 of the blade 16 and the yaw angle 1 of the drawbar 17 are kept constant.

[0071] For example, when the left lift lever 41 is operated to elevate the left end 161 of the blade 16, the controller 36 contracts the left lift cylinder 22. Accordingly, the left end 161 of the blade 16 is elevated. Besides, the controller 36 contracts the right lift cylinder 23. Accordingly, the right end 162 of the blade 16 is inhibited from being lowered. Furthermore, the controller 36 contracts the drawbar shift cylinder 24. Accordingly, the yaw angle 1 of the blade 16 is inhibited from being changed. Consequently, the left end 161 of the blade 16 is elevated in a vertical direction. The vertical direction refers to a direction parallel to a gravitational direction.

[0072] When described in detail, FIG. 14 is a flowchart showing a series of processing of the integrated control for the work implement 5 to be executed by the controller 36. As shown in FIG. 14, in step S101, the controller 36 obtains the current posture of the work implement 5. The controller 36 obtains the current stroke lengths of the hydraulic cylinders 22 to 26 and the current rotational angle 4 of the circle 18 based on the signals transmitted thereto from the plural sensors S1 to S6. The controller 36 calculates the plural parameters described above, indicating the posture of the work implement 5, based on the current stroke lengths of the hydraulic cylinders 22 to 26 and the current rotational angle 4 of the circle 18.

[0073] In step S102, the controller 36 obtains the operation to the operating device 35. The controller 36 receives, from any of the plural operating members 41 to 46 described above, a signal that indicates the operation to the operating member.

[0074] In step S103, the controller 36 determines a target posture. The controller 36 determines the target posture depending on the operation to the operating member. For example, when the left lift lever 41 is being operated, the controller 36 determines both the pitch angle 2 and the roll angle 3 of the drawbar 17 as the target posture such that the height of the left end 161 of the blade 16 become a height corresponding to the operation to the left lift lever 41, while the height of the right end 162 of the blade 16 and the right-and-left directional position of the drawbar 17 are kept constant. It should be noted that the yaw angle 1 of the drawbar 17 is kept in a value corresponding to the initial state of the drawbar 17.

[0075] In step S104, the controller 36 determines a target stroke length. The controller 36 calculates the target stroke lengths for the hydraulic cylinders 22 to 26, respectively, such that the target posture can be taken by the work implement 5. In the example described above, the controller 36 calculates a first target stroke length of the left lift cylinder 22, a second target stroke length of the right lift cylinder 23, and a third target stroke length of the drawbar shift cylinder 24 that realize the pitch angle 2 and the roll angle 3 of the drawbar 17 that indicate the target posture described above.

[0076] In step S105, the controller 36 calculates stroke differences. Each stroke difference refers to a difference between the target stroke length and the current stroke length. In the example described above, the controller 36 determines a difference between the current stroke length and the first target stroke length of the left lift cylinder 22 as a first stroke difference. The controller 36 determines a difference between the current stroke length and the second target stroke length of the right lift cylinder 23 as a second stroke difference. The controller 36 determines a difference between the current stroke length and the third target stroke length of the drawbar shift cylinder 24 as a third stroke difference.

[0077] In step S106, the controller 36 determines target stroke speeds for the hydraulic cylinders 22 to 26, respectively, such that the target posture can be taken by the work implement 5. The controller 36 determines the target stroke speeds based on the stroke differences of the hydraulic cylinders 22 to 26, respectively. In the example described above, the controller 36 determines a first target stroke speed of the left lift cylinder 22 based on the first stroke difference. The controller 36 determines a second target stroke speed of the right lift cylinder 23 based on the second stroke difference. The controller 36 determines a third target stroke speed of the drawbar shift cylinder 24 based on the third stroke difference.

[0078] In step S107, the controller 36 controls the actuators based on the target stroke speeds, respectively. In the example described above, the controller 36 controls the control valve 34 such that the left lift cylinder 22 is actuated to stroke at the first target stroke speed. The controller 36 controls the control valve 34 such that the right lift cylinder 23 is actuated to stroke at the second target stroke speed. The controller 36 controls the control valve 34 such that the drawbar shift cylinder 24 is actuated to stroke at the third target stroke speed. Accordingly, as shown in FIG. 13, the height of the left end 161 of the blade 16 is vertically changed depending on the operation to the left lift lever 41, while the height of the right end 162 of the blade 16 and the right-and-left directional position of the drawbar 17 are kept constant.

[0079] As described above, when the left lift lever 41 is being operated, the controller 36 enables the work implement 5 to take the target posture depending on the operation to the left lift lever 41by the combination of the stroke motions of the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24. Likewise, when any other operating member is being operated, the controller 36 enables the work implement 5 to take the target posture depending on the operation to the operating member by the combination of the actuations of the plural actuators 22 to 27.

[0080] For example, as shown in FIG. 10, when the right lift lever 42 is being operated, the controller 36 actuate the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24. When the right lift cylinder 23 is actuated to stroke in a comparable manner to the left lift cylinder 22, not only the height of the right end 162 of the blade 16 but also both the height of the left end 161 of the blade 16 and the right-and-left directional position of the drawbar 17 are changed depending on the stroke motion of the right lift cylinder 23.

[0081] Because of this, when the right lift lever 42 is being operated, the controller 36 determines both the pitch angle 2 and the roll angle 3 of the drawbar 17 as the target posture such that the right end 162 of the blade 16 is vertically moved and is set at a height depending on the operation to the right lift lever 42, while the height of the left end 161 of the blade 16 and the yaw angle 1 of the drawbar 17 are kept constant. Then, the controller 36 enables the work implement 5 to take the target posture depending on the operation to the right lift lever 42 by the combination of the stroke motions of the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24.

[0082] When the drawbar shift lever 43 is being operated, the controller 36 actuates the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24. FIG. 15A shows a state of the work implement 5 in a well-known motor grader, in which the drawbar shift cylinder 24 is actuated to stroke from the initial state thereof. As shown in FIG. 15A, when the drawbar shift cylinder 24 is actuated to stroke in the well-known motor grader, not only the height of the left end 161 of the blade 16 but also the height of the right end 162 of the blade 16 is changed depending on the stroke motion of the drawbar shift cylinder 24. Besides, the yaw angle 1 of the drawbar 17 is changed depending on the stroke motion of the drawbar shift cylinder 24.

[0083] Because of this, in the work machine 1 according to the present embodiment, when the drawbar shift lever 43 is being operated, as shown in FIG. 15B, the controller 36 determines both the pitch angle 2 and the roll angle 3 of the drawbar 17 as the target posture such that the yaw angle 1 of the drawbar 17 is set depending on the operation to the drawbar shift lever 43, while the height of the left end 161 of the blade 16 and the height of the right end 162 of the blade 16 are kept constant. Besides, the controller 36 enables the work implement 5 to take the target posture depending on the operation to the drawbar shift lever 43 by the combination of the stroke motions of the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24.

[0084] When the rotational lever 44 is being operated, the controller 36 actuates the left lift cylinder 22, the right lift cylinder 23, the drawbar shift cylinder 24, and the rotary actuator 27. FIG. 16A is a side view of the work implement 5 in the initial state thereof. FIG. 16B shows a state of the work implement 5 in the well-known motor grader, in which the circle 18 has been rotated from the initial state thereof. As shown in FIG. 16B, when the circle 18 is rotated by the rotary actuator 27 in the well-known motor grader, not only the height of the left end 161 of the blade 16 but also the height of the right end 162 of the blade 16 is changed depending on the rotation of the circle 18. Besides, the rotational angle 4 of the circle 18 is changed depending on the rotation of the circle 18.

[0085] Because of this, in the work machine 1 according to the present embodiment, when the rotational lever 44 is being operated, as shown in FIG. 16C, the controller 36 determines the yaw angle 1, the pitch angle 2, and the roll angle 3 of the drawbar 17 as the target posture such that the rotational angle 4 of the circle 18 is set depending on the operation to the rotational lever 44, while the height of the left end 161 of the blade 16 and the height of the right end 162 of the blade 16 are kept constant. Besides, the controller 36 enables the work implement 5 to take the target posture depending on the operation to the rotational lever 44 by the combination of the stroke motion of the left lift cylinder 22, the stroke motion of the right lift cylinder 23, the stroke motion of the drawbar shift cylinder 24, and the rotary motion of the rotary actuator 27.

[0086] When the blade tilt lever 45 is being operated, the controller 36 actuates the left lift cylinder 22, the right lift cylinder 23, the drawbar shift cylinder 24, and the blade tilt cylinder 25. FIG. 17A is a side view of the work implement 5 in the initial state thereof. FIG. 17B shows a state of the work implement 5 in the well-known motor grader, in which the blade tilt cylinder 25 has been actuated to stroke from the initial state thereof. As shown in FIG. 17B, when the blade tilt cylinder 25 is actuated to stroke in the well-known motor grader, the height of the blade 16 is changed as well depending on the stroke motion of the blade tilt cylinder 25. Besides, the tilt angle 5 of the blade 16 is changed depending on the stroke motion of the blade tilt cylinder 25.

[0087] Because of this, in the work machine 1 according to the present embodiment, when the blade tilt lever 45 is being operated, as shown in FIG. 17C, the controller 36 determines the yaw angle 1, the pitch angle 2, and the roll angle 3 of the drawbar 17 as the target posture such that the tilt angle 5 of the blade 16 is set depending on the operation to the blade tilt lever 45, while the height of the blade 16 is kept constant. Besides, the controller 36 enables the work implement 5 to take the target posture depending on the operation to the blade tilt lever 45 by the combination of the stroke motions of the left lift cylinder 22, the right lift cylinder 23, the drawbar shift cylinder 24, and the blade tilt cylinder 25.

[0088] It should be noted that, when the blade shift lever 46 is being operated, the controller 36 controls the blade shift cylinder 26 such that the blade 16 is shifted by an amount depending on the operation to the blade shift lever 46.

[0089] In the work machine 1 according to the present embodiment explained above, the target posture of the work implement 5 is determined depending on the operation to the operating device 35. The target stroke lengths of the plural hydraulic cylinders 22 to 26 and the rotational angle 4 of the rotary actuator 27 are determined such that the work implement 5 takes the target posture by the combination of the stroke motions of the plural hydraulic cylinders 22 to 26. Then, based on the target stroke lengths and rotational angle 4 herein determined, the plural hydraulic cylinders 22 to 26 and the rotary actuator 27 are controlled, respectively. Thus, by operating the operating device 35 simply and easily, the stroke motions of the plural hydraulic cylinders 22 to 26 and the rotary motion of the rotary actuator 27 are combined, whereby the work implement 5 is caused to take the target posture. Because of this, operating the work implement 5 is made easy in the work machine 1.

[0090] For example, when the operator operates only the left lift lever 41, the height of the left end 161 of the blade 16 is changed, while the height of the right end 162 of the blade 16 and the right-and-left directional position of the drawbar 17 are kept constant. When the operator operates only the right lift lever 42, the height of the right end 162 of the blade 16 is changed, while the height of the left end 161 of the blade 16 and the right-and-left directional position of the drawbar 17 are kept constant.

[0091] When the operator operates only the drawbar shift lever 43, the yaw angle 1 of the drawbar 17 is changed, while the height of the left end 161 of the blade 16 and the height of the right end 162 of the blade 16 are kept constant. When the operator operates only the rotational lever 44, the rotational angle 4 of the circle 18 is changed, while the height of the left end 161 of the blade 16 and the height of the right end 162 of the blade 16 are kept constant. When the operator operates only the blade tilt lever 45, the tilt angle 5 of the blade 16 is changed, while the height of the left end 161 of the blade 16 and the height of the right end 162 of the blade 16 are kept constant.

[0092] The integrated control explained above is executed when the blade 16 takes a normal posture. Integrated control to be explained next is executed when the blade 16 takes a bank cutting posture. FIG. 18 is a front view of the work implement 5 when the blade 16 takes the normal posture. FIG. 19 is a front view of the work implement 5 when the blade 16 takes the bank cutting posture. In FIGS. 18 and 19, the position of the vehicle body 2 is depicted with dashed two-dotted line. As shown in FIGS. 18 and 19, when taking the bank cutting posture, the blade 16 has a larger roll angle 6 than when taking the normal posture.

[0093] For example, in a work for forming a slope in a terrain, the operator causes the work implement 5 to take the bank cutting posture. As shown in FIG. 19, when taking the bank cutting posture, the blade 16 is kept tilting with respect to a horizontal direction enough to almost reach a vertical direction. In this state, the blade 16 is caused to excavate the terrain, whereby the slope is formed therein.

[0094] For example, the operator changes the posture of the blade 16 from the normal posture to the bank cutting posture as follows. First, the operator operates the lifter lock switch 47 to move the lock pins 51 and 52 out of the lock holes 301, whereby the lifter bracket 29 is turned to the unlocked state. The operator operates the left and right lift levers 41 and 42 to rotate the blade 16 together with the lifter bracket 29 about the front frame 11. The operator stops rotating the blade 16 at a position that the bank cutting posture is taken by the blade 16; then the operator operates the lifter lock switch 47 to move the lock pins 51 and 52 into the lock holes 301, whereby the lifter bracket 29 is turned to the locked state. Accordingly, the blade 16 is kept in the bank cutting posture.

[0095] When the work implement 5 takes such an extreme posture as the bank cutting posture, if the aforementioned integrated control for the normal posture is executed, there is a possibility that operational feeding of the operator is deteriorated due to deviation between operating the operating device 35 and the actuation of the blade 16. For example, in the work for forming a slope in a terrain, chances are that the operator moves the blade 16 in a direction oriented perpendicular to the slope to press the blade 16 onto the slope. In this case, under the aforementioned integrated control for the normal posture, when the operator operates the left and right lift levers 41 and 42 simultaneously, the blade 16 is undesirably moved not in the direction oriented perpendicular to the slope but in the vertical direction. Because of this, the operator is required to operate not only the left and right lift levers 41 and 42 but also another lever simultaneously, whereby the operational feeding of the operator is rather deteriorated undesirably. In view of this, as explained below, when the blade 16 takes the bank cutting posture, the controller 36 executes the integrated control in a different control mode from the aforementioned integrated control executed when the blade 16 takes the normal posture.

[0096] FIG. 20 is a flowchart showing a series of processing of the integrated control executed by the controller 36. As shown in FIG. 20, in step S201, the controller 36 obtains the current posture of the blade 16. The controller 36 obtains the current posture of the blade 16 based on the roll angle 6 of the blade 16. The roll angle 6 of the blade 16 is set as, for instance, a tilt angle of the blade 16 with respect to the ground 100. Alternatively, the roll angle 6 of the blade 16 may be set as a tilt angle of the blade 16 with respect to the vehicle body 2. The controller 36 obtains the roll angle 6 of the blade 16 based on, for instance, the roll angle 3 of the drawbar 17 described above.

[0097] In step S202, the controller 36 determines whether or not the current posture of the blade 16 is the bank cutting posture. The controller 36 determines whether or not the posture of the blade 16 is the bank cutting posture based on the roll angle 6 of the blade 16. The controller 36 determines that the current posture of the blade 16 is the bank cutting posture, for instance, when the roll angle 6 of the blade 16 is greater than a predetermined threshold. The controller 36 determines that the current posture of the blade 16 is not the bank cutting posture but the normal posture when the roll angle 6 of the blade 16 is less than or equal to the predetermined threshold. When the controller 36 determines that the current posture of the blade 16 is the normal posture, the processing proceeds to step S203.

[0098] In step S203, the controller 36 selects a first mode as a mode of the integrated control for the blade 16. In other words, when the current posture of the blade 16 is the normal posture, the controller 36 selects the first mode as a control mode for the blade 16. Then, in step S204, the integrated control is executed in the first mode. In the first mode, the controller 36 executes a series of processing comparable to that of the integrated control described above.

[0099] As shown in FIG. 18, under the integrated control in the first mode, the controller 36 controls the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24 such that the blade 16 is moved in a vertical direction H1, H2 depending on the operation to the left and right lift levers 41 and 42. For example, when the operator operates only the left lift lever 41, the controller 36 controls the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24 such that the left end 161 of the blade 16 is moved in the vertical direction H1. When the operator operates only the right lift lever 42, the controller 36 controls the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24 such that the right end 162 of the blade 16 is moved in the vertical direction H2.

[0100] When the operator operates both the left and right lift levers 41 and 42 by an identical amount, the controller 36 controls the plural actuators such that translation (parallel displacement) is made for the entirety of the blade 16 in the vertical direction H1, H2. For example, when the operator operates the left and right lift levers 41 and 42 upward in a comparable manner, the controller 36 controls the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24 such that upward translation is made for the entirety of the blade 16 in the vertical direction H1, H2. When the operator operates the left and right lift levers 41 and 42 downward in a comparable manner, the controller 36 controls the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24 such that downward transmission is made for the entirety of the blade 16 in the vertical direction H1, H2.

[0101] In step S202, when the current posture of the blade 16 is the bank cutting posture, the processing proceeds to step S205. In step S205, the controller 36 selects a second mode as a mode of the integrated control for the blade 16. Then, in step S204, the integrated control is executed in the second mode.

[0102] As shown in FIG. 19, under the integrated control in the second mode, the controller 36 controls the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24 such that the blade 16 is moved in a blade normal line direction H3, H4 depending on the operations to the left and right lift levers 41 and 42. The blade normal line direction H3, H4 refers to a direction oriented perpendicular to the lengthwise direction of the blade 16. For example, when the operator operates only the left lift lever 41, the controller 36 controls the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24 such that the left end 161 of the blade 16 is moved in the blade normal line direction H3. When the operator operates only the right lift lever 42, the controller 36 controls the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24 such that the right end 162 of the blade 16 is moved in the blade normal line direction H4.

[0103] When the operator operates the left and right lift levers 41 and 42 in a comparable manner, the controller 36 controls the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24 such that translation is made for the entirety of the blade 16 in the blade normal line direction H3, H4. For example, when the operator upwardly operates the left and right lift levers 41 and 42 in a comparable manner, the controller 36 controls the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24 such that upward translation is made for the entirety of the blade 16 in the blade normal line direction H3, H4. When the operator downwardly operates the left and right lift levers 41 and 42 in a comparable manner, the controller 36 controls the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24 such that downward translation is made for the entirety of the blade 16 in the blade normal line direction H3, H4.

[0104] In the work machine 1 according to the present embodiment explained above, either the first or second mode is selected depending on the posture of the blade 16. In the first mode, the plural actuators are controlled such that the blade 16 is moved in the vertical direction H1, H2 depending on the operations to the left and right lift levers 41 and 42. In the second mode, the plural actuators are controlled such that the blade 16 is moved in the blade normal line direction H3, H4 depending on the operations to the left and right lift levers 41 and 42. Accordingly, the operation for changing the posture of the work implement 5 is made easy. Besides, even when the blade 16 takes an extreme posture such as the bank cutting posture, deterioration in operational feeling is inhibited.

[0105] One embodiment of the present invention has been explained above. However, the present invention is not limited to the embodiment described above and a variety of changes can be made without departing from the gist of the present invention.

[0106] The work machine 1 is not limited to the motor grader and may be another type of work machine such as a bulldozer. The parameters indicating the posture of the work implement 5 are not limited to those in the embodiment described above and may be changed. The plural operating members 41 to 46 are not limited to those in the embodiment described above and may be changed. For example, the operating members are not limited to levers and may be another type of members such as one or more joysticks, switches, one or more touchscreens, or so forth.

[0107] The sensors for detecting the posture of the work implement 5 are not limited to those in the embodiment described above and may be changed. For example, the sensors may be inertia measurement units (IMUs). The IMUs may be attached to the drawbar 17 and either the front frame 11 or the vehicle body 2, respectively. The posture of the drawbar 17 and that of the front frame 11 may be detected by the IMUs.

[0108] The number of modes for the integrated control is not limited to two and may be greater than two. In other words, one or more modes other than the first and second modes described above may be selectable. The postures taken by the blade 16 are not limited to the normal posture and the bank cutting posture described above and may further include another posture.

[0109] The actuators to be actuated when the left and right lift levers 41 and 42 are operated are not limited to the combination of the left lift cylinder 22, the right lift cylinder 23, and the drawbar shift cylinder 24. For example, the blade shift cylinder 26 may be added to the combination of actuators.

[0110] The posture of the blade 16 may not be determined by the roll angle 6 of the blade 16, and instead, may be determined by another parameter. For example, FIG. 21 is a schematic view of the drive train 6 and the control system 7 in the work machine 1 according to a modification. As shown in FIG. 21, the work machine 1 may include a lifter bracket sensor S7. As shown in FIG. 22, the lifter bracket sensor S7 detects a rotational angle 7 of the lifter bracket 29 with respect to the front frame 11. The rotational angle 7 of the lifter bracket 29 refers to a rotational angle of the lifter bracket 29 from a predetermined reference position with respect to the front frame 11.

[0111] The lifter bracket sensor S7 may be, for instance, a proximity sensor. The lifter bracket sensor S7 may be disposed between the lifter bracket 29 and the front frame 11. Alternatively, the lifter bracket sensors S7 may be disposed between the lock pins 51 and 52 of the lifter bracket 29 and the lock holes 301 of the lifter guide 30. For example, based on to which of the lock holes 301 the lock pins 51 and 52 are fitted, it may be determined whether or not the blade 16 takes the bank cutting posture.

[0112] The controller 36 may determine which of the normal posture and the bank cutting posture is taken by the blade 16 based on the rotational angle 7 of the lifter bracket 29. For example, when the rotational angle 7 of the lifter bracket 29 is greater than a predetermined threshold, the controller 36 may determine that the blade 16 takes the bank cutting posture. When the rotational angle 7 of the lifter bracket 29 is less than or equal to the predetermined threshold, the controller 36 may determine that the blade 16 takes the normal posture.

[0113] According to the present invention, an operation for changing the posture of a work implement is made easy; simultaneously, degradation in operational feeling attributed to the posture of the work implement is inhibited.