Work Machine and Method for Controlling Work Machine

This application is a U.S. National stage application of International Application No. PCT/JP2023/026577, filed on Jul. 20, 2023. This U.S. National stage application claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2022-141377, filed in Japan on Sep. 6, 2022, the entire contents of which are hereby incorporated herein by reference.

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

A work machine includes a vehicle body, a work implement, and an actuator. The actuator is, for example, a hydraulic cylinder. The actuator is driven in response to an operation by an operator, thereby causing the work implement to move. For example, a motor grader includes a blade as the work implement. The motor grader includes a tandem drive and a frame as the vehicle body. The blade is supported by the frame. The frame supports a front wheel so that the front wheel is rotatable. The tandem drive supports a rear wheel. The operator operates an operating lever of the work implement, thereby causing the blade to move up and down.

In the aforementioned motor grader, the posture of the frame changes when the front wheel travels over an undulation, resulting in a change in height of the blade. A technique that addresses this problem is disclosed in Japanese Patent Publication No. 2001-193095. In Japanese Patent Publication No. 2001-193095, a controller calculates a change in height of the blade from a relative rotation angle between the frame and the tandem drive. The controller causes the blade to move up and down according to the change in height of the blade. As a result, the blade is maintained at a predetermined height.

However, in the motor grader of Japanese Patent Publication No. 2001-193095, when the posture of the entire vehicle body including the tandem drive changes, the height direction of the blade with respect to the vehicle body also changes. For example, when the tandem drive is tilted from a horizontal surface, the height of the blade calculated by the controller takes a value different from the actual height of the blade. Therefore, it is difficult to accurately maintain the blade at a predetermined height with respect to the ground. An object of the present disclosure is to accurately maintain a work implement at a target height even when a work machine travels on a ground with undulations.

One aspect of the present disclosure is a work machine that includes a vehicle body, a work implement, an actuator, and a controller. The work implement is supported so as to be movable with respect to the vehicle body. The actuator is connected to the work implement. The actuator causes the work implement to move. The controller performs an automatic control for controlling the actuator so that a height of the work implement in a gravity direction is maintained even when a posture of the vehicle body changes. The controller determines whether the work machine is in a non-working state in which the work machine does not perform work with the work implement. The controller stops the automatic control when the work machine is in the non-working state.

Another aspect of the present disclosure is a method for controlling a work machine. The work machine includes a vehicle body, a work implement, and an actuator. The work implement is supported so as to be movable with respect to the vehicle body. The actuator is connected to the work implement. The actuator causes the work implement to move. The method includes performing an automatic control for controlling the actuator so that a height of the work implement in a gravity direction is maintained even when a posture of the vehicle changes, determining whether the work machine is in a non-working state in which the work machine does not perform work with the work implement, and stopping the automatic control when the work machine is in the non-working state.

According to the present disclosure, the height of the work implement in the gravity direction is maintained by the automatic control even when the posture of the vehicle body changes. Therefore, even when the work machine travels on the ground with undulations, the height of the work implement is accurately maintained. Further, the automatic control is stopped when the work machine is in the non-working state in which the work machine does not perform work with the work implement. As a result, it is possible to reduce an unintended movement of the work implement while the work machine is not performing work.

An embodiment of the present disclosure will be described below with reference to the drawings.is a side view of a work machineaccording to the embodiment.is a perspective view of a front part of the work machine. The work machineaccording to the present embodiment is a motor grader. As illustrated in, the work machineincludes a vehicle bodyand a work implement. The work implementis supported so as to be movable with respect to the vehicle body. The vehicle bodyincludes a vehicle body frame, a tandem drive, front wheels, and rear wheelsA andB.

The vehicle body framesupports the front wheelsand the work implement. The vehicle body frameincludes a front frameand a rear frame. The rear frameis connected to the front frame. The front frameis configured to articulate to the left and right with respect to the rear frame. In the following description, the front, rear, left, and right directions means the front, rear, left, and right directions of the vehicle bodywhile the articulation angle is zero, that is, while the front frameand the rear frameare straight.

A caband a power compartmentare disposed on the rear frame. An unillustrated operator's seat is disposed in the cab. A drive system which will be described below is disposed in the power compartment. The front frameextends forward from the rear frame. The front wheelsare attached to the front frame.

The tandem driveis connected to the rear frame. The tandem drivesupports the rear wheelsA andB and drives the rear wheelsA andB. The tandem driveincludes a rear axisthat extends in the left-right direction. The tandem drivesupports the rear frameof the vehicle body frameso that the rear frameis swingable about the rear axis. When the front wheelsmove up and down due to undulations of a road surface that is not graded by the work implement, the vehicle body frameswings about the rear axis(see).

The rear wheelsA andB include a pair of first rear wheelsA and a pair of second rear wheelsB. In, only the first rear wheelA at the left side and the second rear wheelB at the left side are illustrated. The second rear wheelsB are disposed behind the first rear wheelsA. The rear axisis disposed between the first rear wheelsA and the second rear wheelsB. The rear axisserves as the center of swing of the vehicle body framewith respect to the tandem drive.

The work implementis movably connected to the vehicle body. The work implementincludes a supporting memberand a blade. The supporting memberis movably connected to the vehicle body. The supporting membersupports the blade. The supporting memberincludes a drawbarand a circle. The drawbarand the circleare disposed below the front frame.

As illustrated in, the drawbaris connected to a shaft support partof the front frame. The shaft support partis disposed at a front part of the front frame. The drawbarextends rearward from the front part of the front frame. The drawbaris supported so as to be swingable at least in the up-down direction and the left-right direction of the vehicle bodywith respect to the front frame. For example, the shaft support partincludes a ball joint. The drawbaris rotatably connected to the front framevia the ball joint.

The circleis connected to a rear part of the drawbar. The circleis supported so as to be rotatable with respect to the drawbar. The bladeis connected to the circle. The bladeis supported by the drawbarvia the circle. The bladeis supported by the circleso as to be rotatable about a tilt shaft. The tilt shaftextends in the left-right direction. The bladeis supported by the circleso as to be slidable in the left-right direction.

The work machineincludes a plurality of actuatorstofor changing the posture of the work implement. The plurality of actuatorstoinclude a plurality of hydraulic cylindersto. The plurality of hydraulic cylinderstoare connected to the work implement. The plurality of hydraulic cylinderstoextend and contract due to hydraulic pressure. The plurality of hydraulic cylinderstoextend and contract, thereby changing the posture of the work implementwith respect to the vehicle body. In the following explanation, the extension and contraction of the hydraulic cylinder is referred to as a “stroke motion”.

Specifically, the plurality of hydraulic cylinderstoinclude a left lift cylinder, a right lift cylinder, a drawbar shift cylinder, a blade tilt cylinder, and a blade shift cylinder. The left lift cylinderand the right lift cylinderare disposed apart from each other in the left-right direction. The left lift cylinderis connected to a left part of the drawbar. The right lift cylinderis connected to a right part of the drawbar. The left lift cylinderand the right lift cylinderare connected so as to be swingable to the left and right with respect to the draw bar.

The left lift cylinderand the right lift cylinderare connected so as to be swingable to the left and right with respect to the front frame. Specifically, the left lift cylinderand the right lift cylinderare connected to the front framevia a lifter bracket. The lifter bracketis connected to the front frame. The lifter bracketsupports the left lift cylinderand the right lift cylinderso that the left lift cylinderand the right lift cylinderare swingable to the left and right. Due to the stroke motions of the left lift cylinderand the right lift cylinder, the drawbarswings up and down about the shaft support part. As a result, the blademoves up and down.

The drawbar shift cylinderis connected to the drawbarand the front frame. The drawbar shift cylinderis connected to the front framevia the lifter bracket. The drawbar shift cylinderis connected so as to be swingable with respect to the front frame. The drawbar shift cylinderis connected so as to be swingable with respect to the drawbar. The drawbar shift cylinderextends diagonally downward from the front frametoward the drawbar. The drawbar shift cylinderextends to the left and right from one side to the opposite side of the front frame. Due to the stroke motion of the drawbar shift cylinder, the drawbarswings to the left and right about the shaft support part.

As illustrated in, the blade tilt cylinderis connected to the circleand the blade. The bladerotates about the tilt shaftdue to the stroke motion of the blade tilt cylinder. As illustrated in, the blade shift cylinderis connected to the circleand the blade. The bladeslides to the left and right with respect to the circledue to the stroke motion of the blade shift cylinder.

The plurality of actuatorstoinclude a rotary actuator. The rotary actuatoris connected to the drawbarand the circle. The rotary actuatorcauses the circleto rotate with respect to the drawbar. As a result, the bladerotates about a rotation axis that extends in the up-down direction.

is a schematic diagram illustrating a drive systemand a control systemof the work machine. As illustrated in, the work machineincludes a drive source, a hydraulic pump, a power transmission device, and a control valve. The drive sourceis, for example, an internal combustion engine. Alternatively, the drive sourcemay be an electric motor or a hybrid of an internal combustion engine and an electric motor. The hydraulic pumpis driven by the drive sourceto discharge hydraulic fluid.

The control valveis connected to the hydraulic pumpand the plurality of hydraulic cylinderstothrough a hydraulic circuit. The control valveincludes a plurality of valves respectively connected to the plurality of hydraulic cylindersto. The control valvecontrols the flow rate of hydraulic fluid supplied from the hydraulic pumpto the plurality of hydraulic cylindersto.

In the present embodiment, the rotary actuatoris a hydraulic motor. The control valveis connected to the hydraulic pumpand the rotary actuatorthrough a hydraulic circuit. The control valvecontrols the flow rate of hydraulic fluid supplied from the hydraulic pumpto the rotary actuator. The rotary actuatormay be an electric motor.

The power transmission devicetransmits the driving force from the drive sourceto the rear wheelsA andB. The power transmission devicemay include a torque converter and/or a plurality of speed change gears. Alternatively, the power transmission devicemay be a transmission such as a hydraulic static transmission (HST) or a hydraulic mechanical transmission (HMT). The work machineincludes a shift operating member. The shift operating memberis operable at a neutral position N, a forward position F, and a reverse position R. The power transmission deviceswitches a travel mode between forward, reverse, and neutral according to the operating position of the shift operating member.

As illustrated in, the work machineincludes an operating deviceand a controller. The operating deviceis operable by an operator for changing the posture of the work implement. The posture of the work implementindicates a position and an orientation of the bladewith respect to the vehicle body.is a schematic rear view of the work machineillustrating the posture of the work implement machine. As illustrated in, the height of a left end portionand the height of a right end portionof the bladeare changed according to an operation of the operating device.

A yaw angle θ, a pitch angle θ, and a roll angle θof the drawbarare changed according to an operation of the operating device.is a schematic plan view of the work machineillustrating the posture of the work implement. As illustrated in, the yaw angle θof the drawbaris a tilt angle of the drawbarin the left-right direction with respect to the front-rear direction of the vehicle body. The yaw angle θof the drawbarmay be a tilt angle of the drawbarin the left-right direction with respect to the front-rear direction of the front frame. The position of the bladein the left-right direction changes according to the yaw angle θof the drawbar.

is a schematic side view of the work machineillustrating the posture of the work implement. As illustrated in, the pitch angle θof the drawbaris a tilt angle of the drawbarin the up-down direction with respect to the front-rear direction of the vehicle body. As illustrated in, the roll angle θof the drawbaris a tilt angle of the drawbarabout a roll axis Al that extends in the front-rear direction of the vehicle body.

According to an operation of the operating device, a rotation angle θof the circle, a tilt angle θof the blade, and a shift amount Wof the bladeare changed.is a schematic plan view of the work machineillustrating the posture of the work implement. As illustrated in, the rotation angle θof the circleis the rotation angle θof the circlewith respect to the front-rear direction of the vehicle body. As illustrated in, the tilt angle θof bladeis a tilt angle of the bladeabout the tilt shaftthat extends in the left-right direction.is a schematic plan view of the work machineillustrating the posture of the work implement. As illustrated in, the shift amount Wof the bladeis an amount by which the bladeslides in the left-right direction with respect to the circle.

The operating deviceincludes a plurality of operating membersto. The plurality of operating memberstoare provided respectively corresponding to the left lift cylinder, the right lift cylinder, the drawbar shift cylinder, the blade tilt cylinder, the blade shift cylinder, and the rotary actuator.

The plurality of operating memberstoinclude a left lift lever, a right lift lever, a drawbar shift lever, a rotation lever, a blade tilt lever, and a blade shift lever. The left lift cylinderextends and contracts according to an operation of the left lift lever. The right lift cylinderextends and contracts according to an operation of the right lift lever.

The drawbar shift cylinderextends and contracts according to an operation of the drawbar shift lever. The rotary actuatorrotates according to an operation of the rotation lever. The blade tilt cylinderextends and contracts according to an operation of the blade tilt lever. The blade shift cylinderextends and contracts according to an operation of the blade shift lever. Each of the plurality of operating memberstooutputs a signal indicative of the operation by the operator for each of the operating membersto.

The controllercontrols the drive sourceand the power transmission device, thereby causing the work machineto travel. Further, the controllercontrols the hydraulic pumpand the control valve, thereby causing the work implementto move. The controllerincludes a processorand a storage device. The processoris, for example, a CPU and executes a program for controlling the work machine. The storage deviceincludes a memory such as a RAM or a ROM, and an auxiliary storage devices such as an SSD or an HDD. The storage devicestores programs and data for controlling the work machine.

As illustrated in, the work machineincludes a work implement sensorfor detecting the posture of the work implementdescribed above. The work implement sensorincludes a plurality of sensors Sto S. The plurality of sensors Sto Sare, for example, magnetic sensors. The plurality of sensors Sto Smay be sensors of another type such as an optical sensor. The plurality of sensors Sto Sdetect stroke lengths of the plurality of hydraulic cylinderstodescribed above. The plurality of sensors Sto Sinclude a left lift sensor S, a right lift sensor S, a drawbar shift sensor S, a blade tilt sensor S, and a blade shift sensor S.

The left lift sensor Sdetects a stroke length of the left lift cylinder. The right lift sensor Sdetects a stroke length of the right lift cylinder. The drawbar shift sensor Sdetects a stroke length of the drawbar shift cylinder. The blade tilt sensor Sdetects a stroke length of the blade tilt cylinder. The blade shift sensor Sdetects a stroke length of the blade shift cylinder.

The plurality of sensors Sto Sinclude a rotation sensor S. The rotation sensor Sdetects the rotation angle θof the circle. The plurality of sensors Sto Soutput signals indicative of the stroke lengths and the rotation angle θdetected by the respective sensors. The plurality of sensors Sto Sinclude a left cylinder angle sensor Sand a right cylinder angle sensor S. The left cylinder angle sensor Sdetects a swing angle of the left lift cylinderin the left-right direction with respect to the lifter bracket. The right cylinder angle sensor Sdetects a swing angle of the right lift cylinderin the left-right direction with respect to the lifter bracket. By means of these sensors Sto S, a posture of the drawbarwith respect to the vehicle bodyis detected and a posture of the bladewith respect to the draw baris detected. That is, the posture of the bladewith respect to the vehicle bodyis detected by these sensors Sto S.

The work machineincludes a vehicle body sensorand a vehicle speed sensor. The vehicle speed sensordetects the vehicle speed of the work machine. The vehicle body sensoris, for example, an inertial measurement unit (IMU). The vehicle body sensordetects vehicle body posture data indicative of a posture of the vehicle body. The vehicle body posture data includes a pitch angle and a roll angle of the vehicle body. Note that the vehicle body sensoris not limited to the IMU. The vehicle body sensormay be any means that measures the pitch angle and the roll angle of the vehicle body, and may be an inclinometer, for example.

The vehicle body sensoris attached to the vehicle body frame. Therefore, as illustrated in, a pitch angleof the vehicle bodyis a tilt angle of the vehicle body framein the up-down direction with respect to a horizontal direction. As illustrated in, a roll angleof the vehicle bodyis a tilt angle of the vehicle body framein the left-right direction with respect to the horizontal direction. Note that the vehicle body sensormay be attached to another place on the vehicle bodywhere the position relative to the vehicle body framedoes not change, instead of the vehicle body frame. For example, the vehicle body sensormay be disposed on any of other places excluding the tandem driveor the drawbarwhere the position relative to the vehicle body framechanges.

The controlleracquires work implement posture data indicative of the posture of the work implementwith respect to the vehicle bodybased on a signal from the work implement sensor. The work implement posture data includes the height of the left end portionand the height of the right end portionof the blade, the yaw angle θ, the pitch angle θ, the roll angle θof the drawbar, the rotation angle θof the circle, the tilt angle θof the blade, and the shift amount Wof the bladedescribed above. The controlleracquires the vehicle body posture data based on a signal from the vehicle body sensor. The controllercontrols the plurality of actuatorstoaccording to the operations of the plurality of operating membersto, thereby changing the posture of the work implement.

Further, the controllerperforms an automatic control of the work implementbased on the aforementioned vehicle body posture data and work implement posture data. The controllercontrols the left lift cylinderand the right lift cylinderso that the work implementis maintained at a target height under the automatic control of the work implement. Processes of the automatic control of the work implementwill be described as below.is a flowchart illustrating the processes of the automatic control of the work implement.

As illustrated in, in step S, the controllerdetermines whether the operating deviceis being operated. The controllermay determine that the operating deviceis no longer operated when an operation input on the operating deviceis not performed for a certain period of time. When at least one of the aforementioned operating memberstois being operated, the controllerdoes not perform the automatic control of the work implement. Therefore, the controllercontrols the plurality of actuatorstoaccording to the operations of the plurality of operating membersto, thereby changing the posture of the work implement. When the operating memberstoare not being operated, the process proceeds to step S.

In step S, the controlleracquires a current posture of the vehicle body. Here, the controlleracquires the current posture of the vehicle bodyfrom the vehicle body posture data. In step S, the controlleracquires a current posture of the work implement. Here, the controlleracquires the current posture of the work implementfrom the work implement posture data.

In step S, the controllercalculates a current height of the work implement. The controllercalculates the height of the work implementbased on the vehicle body posture data and the work implement posture data. For example, the height of the work implementis the height of the left end portionand the height of the right end portionof the blade. Here, the height of the work implementmeans the height in the gravity direction from an origin Otaking the origin Oof the vehicle bodyillustrated inas a reference point. For example, the height of the work implementmeans the height of the work implementin the gravity direction from a horizontal surface including the origin Oof the vehicle body.

As illustrated in, in a case where the work machineperforms work while traveling forward, the origin Oof the vehicle bodyis positioned on the tandem drive. For example, the origin Oof the vehicle bodyis positioned at the center of the rear axisin the left-right direction. In, a Zaxis indicates the gravity direction. An Xaxis indicates the front-rear direction of the vehicle bodythat is perpendicular to the gravity direction. In, a Yaxis indicates the left-right direction of the vehicle bodythat is perpendicular to the gravity direction. The posture of the vehicle bodychanges about the origin Oof the vehicle body. For example, as illustrated in, the pitch angle θof the vehicle bodychanges about the origin O. As illustrated in, the roll angleof the vehicle bodychanges about the origin O.

In step S, the controllerdetermines a target posture of the work implement. The controllercalculates the target posture of the work implementso that the height of the work implementis the target height. Note that the controllerstores, as the target height, the height of the work implementwhen it is determined that the operating deviceis no longer operated. For example, the controllercalculates a target pitch angle and a target roll angle of the drawbarso that the height of the work implementis the target height.

In step S, the controllercontrols at least one of the actuatorstoso that the height of the work implementis the target height. For example, the controllercontrols the lift cylindersandand the drawbar shift cylinderso that the pitch angle θof the drawbaris the target pitch angle and the roll angle θof the drawbaris the target roll angle.

In this case, the controllercontrols the lift cylindersandand the drawbar shift cylinderso that a position of the bladein the left-right position does not change. That is, in the work machine, due to the extension and contraction of the lift cylindersand, not only the height direction of the bladebut also the position of the blade in the left-right changes. Therefore, the controllercontrols the drawbar shift cylinderso as to offset a change in position of the bladein the left-right position due to the extension and contraction of the lift cylindersand. As a result, the height of the work implementis maintained at the target height and the position of the work implementin the left-right direction is maintained.

By repeating the aforementioned processes of steps Sto S, the controllercontrols the actuatorstoso that the work implementis maintained at the target height. When the operating deviceis operated during the automatic control, the controllerends the automatic control (step S).

With the work machineaccording to the present embodiment described above, the work implementis maintained at the target height of the work implementby the automatic control. The target height is the height in the gravity direction from the origin Oof the vehicle body, and the work implementis maintained at the target height of the work implementeven when the posture of the vehicle bodychanges. Therefore, the work implementis accurately maintained at the target height even when the work machinetravels on a ground with undulations.