Control system for work vehicle, control method, and work vehicle

A work vehicle control system includes an actual topography acquisition device, a storage device, and a controller. The actual topography acquisition device acquires actual topography information, which indicates an actual topography of a work target. The storage device stores design topography information, which indicates a final design topography that is a target topography of the work target. The controller acquires the actual topography information from the actual topography acquisition device, and the design topography information from the storage device. The controller determines an intermediate design topography positioned above the actual topography and below the final design topography. The controller generates a command signal to move the work implement based on the intermediate design topography. The intermediate design topography includes a plurality of intermediate design surfaces divided in the traveling direction of the work vehicle. Inclination angles of at least two of the intermediate design surfaces differ from each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National stage application of International Application No. PCT/JP2017/026915, filed on Jul. 25, 2017. This U.S. National stage application claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2016-146383, filed in Japan on Jul. 26, 2016, the entire contents of which are hereby incorporated herein by reference.

BACKGROUND

Field of the Invention

The present invention relates to a control system for a work vehicle, a control method, and a work vehicle.

Background Information

An automatic control for automatically adjusting the position of a work implement has been conventionally proposed for work vehicles such as bulldozers or graders and the like. For example, Japanese Patent Publication No. 5247939 discloses excavation control and leveling control.

Under the excavation control, the position of the blade is automatically adjusted such that the load applied to the blade coincides with a target load. Under the leveling control, the position of the blade is automatically adjusted so that the tip of the blade moves along a design topography which describes a target shape of the excavation target.

SUMMARY

Work conducted by a work vehicle includes filling work as well as excavating work. During filling work, the work vehicle removes soil from a cutting with the work implement. The work vehicle then piles the removed soil in a predetermined position and compacts the piled soil by traveling over the piled soil. As a result for example, the depressed topography is filled in and a flat shape can be formed.

However, it is difficult to perform desirable filling work under the abovementioned automatic controls. For example as indicated inFIG. 20, in the leveling control, the position of the blade is automatically adjusted so that a blade tip200of the blade moves along a design topography100. As a result, when the filling work is performed with the leveling control, a large amount of soil is piled at one time in a position in front of the work vehicle300as illustrated inFIG. 20by the dashed line. In this case, it is difficult to compact the piled soil because the height of the piled soil is too large. As a result, there is a problem that the quality of the finished work is poor.

In addition, when the work vehicle travels over the actual topography having a steep slope, the attitude of the work vehicle may be suddenly changed. For example, the attitude of the work vehicle may change greatly when traveling over the top of the slope or the bottom of the slope. In this case, there is a problem that the quality of the work finish may deteriorate due to a delay in the tracking of the work implement with respect to the sudden change in the attitude. Sufficiently reducing the speed of the work vehicle could be thought of in order to prevent deterioration in the quality when traveling over the top or bottom of the slope. However in such a case, there is a problem that work efficiency is reduced.

An object of the present invention is to provide a control system for a work vehicle, a control method, and a work vehicle that enable filling work to be performed that is efficient and exhibits a quality finish using automatic controls.

A work vehicle control system according to a first aspect is provided with an actual topography acquisition device, a storage device, and a controller. The actual topography acquisition device acquires actual topography information which indicates an actual topography of a work target. The storage device stores design topography information which indicates a final design topography which is a target topography of the work target. The controller acquires the actual topography information from the actual topography acquisition device. The controller acquires the design topography information from the storage device. The controller determines an intermediate design topography that is positioned above the actual topography and below the final design topography. The controller generates a command signal to move the work implement on the basis of the intermediate design topography. The intermediate design topography includes a plurality of intermediate design surfaces that are divided in the traveling direction of the work vehicle. The inclination angles of the intermediate design surfaces differ from each other among at least two intermediate design surfaces.

A control method of the work vehicle according to a second aspect includes the following steps. Actual topography information is acquired in a first step. The actual topography information indicates the actual topography of a work target. Design topography information is acquired in a second step. The design topography information indicates a final design topography which is a target topography of a work target. An intermediate design topography that is positioned above the actual topography and below the final design topography is determined in a third step. A command signal to move the work implement on the basis of the intermediate design topography is generated in a fourth step. The intermediate design topography includes a plurality of intermediate design surfaces that are divided in the traveling direction of the work vehicle. The inclination angles of the intermediate design surfaces differ from each other among at least two intermediate design surfaces.

A work vehicle according to a third aspect is provided with a work implement and a controller. The controller acquires actual topography information. The actual topography information indicates the actual topography of a work target. The controller acquires design topography information. The design topography information indicates a final design topography of the work target. The controller determines an intermediate design topography that is positioned above the actual topography and below the final design topography. The controller generates a command signal for moving the work implement on the basis of the intermediate design topography. The intermediate design topography includes a plurality of intermediate design surfaces that are divided in the traveling direction of the work vehicle. The inclination angles of the intermediate design surfaces differ from each other among at least two intermediate design surfaces.

According to the present invention, the work implement is controlled on the basis of the intermediate design topography which is positioned below the final design topography. As a result, soil can be piled thinly on the actual topography in comparison to a case of moving the work implement along the final design topography. Consequently, the piled up soil can be easily compacted by the work vehicle and the quality of the finish of the work can be improved.

In addition, the inclination angles of the intermediate design surfaces differ from each other among at least two intermediate design surfaces. Therefore, an intermediate design topography that is more gently sloped can be easily generated. As a result, a sudden change in the attitude of the work vehicle can be suppressed. Consequently, unnecessary speed reduction of the work vehicle can be suppressed and work efficiency can be improved.

DETAILED DESCRIPTION OF EMBODIMENT(S)

A work vehicle according to an embodiment shall be explained in detail with reference to the drawings.FIG. 1is a side view of the work vehicle1according to an embodiment. The work vehicle1is a bulldozer according to the present embodiment. The work vehicle1is provided with a vehicle body11, a travel device12, and a work implement13.

The vehicle body11has an operating cabin14and an engine compartment15. An operator's seat that is not illustrated is disposed inside the operating cabin14. The engine compartment15is disposed in front of the operating cabin14. The travel device12is attached to a bottom part of the vehicle body11. The travel device12has a pair of left and right crawler belts16. Only the right crawler belt16is illustrated inFIG. 1. The work vehicle1travels due to the rotation of the crawler belts16.

The work implement13is attached to the vehicle body11. The work implement13has a lift frame17, a blade18, a lift cylinder19, an angle cylinder20, and a tilt cylinder21.

The lift frame17is attached to the vehicle body11in a manner that allows movement up and down centered on an axis X that extends in the vehicle width direction. The lift frame17supports the blade18. The blade18is disposed in front of the vehicle body11. The blade18moves up and down accompanying the up and down motions of the lift frame17.

The lift cylinder19is coupled to the vehicle body11and the lift frame17. Due to the extension and contraction of the lift cylinder19, the lift frame17rotates up and down centered on the axis X.

The angle cylinder20is coupled to the lift frame17and the blade18. Due to the extension and contraction of the angle cylinder20, the blade18rotates around an axis Y that extends in roughly the up-down direction.

The tilt cylinder21is coupled to the lift frame17and the blade18. Due to the extension and contraction of the tilt cylinder21, the blade18rotates around an axis Z that extends in roughly the front-back direction of the vehicle.

FIG. 2is a block diagram illustrating a configuration of a drive system2and a control system3of the work vehicle1. As illustrated inFIG. 2, the drive system2is provided with an engine22, a hydraulic pump23, and a power transmission device24.

The hydraulic pump23is driven by the engine22to discharge operating fluid. The operating fluid discharged from the hydraulic pump23is supplied to the lift cylinder19, the angle cylinder20, and the tilt cylinder21. While only one hydraulic pump23is illustrated inFIG. 2, a plurality of hydraulic pumps may be provided.

The power transmission device24transmits driving power from the engine22to the travel device12. The power transmission device24, for example, may be a hydrostatic transmission (HST). Alternatively, the power transmission device24, for example, may be a transmission having a torque converter or a plurality of speed change gears.

The control system3is provided with an operating device25, a controller26, and a control valve27. The operating device25is a device for operating the work implement13and the travel device12. The operating device25is disposed in the operating cabin4. The operating device25receives operations from an operator for driving the work implement13and the travel device12, and outputs operation signals in accordance with the operations. The operating device25includes, for example, an operating lever, a pedal, and a switch and the like.

The controller26is programmed to control the work vehicle1on the basis of acquired information. The controller26includes, for example, a processor such as a CPU. The controller26acquires operation signals from the operating device25. The controller26controls the control valve27on the basis of the operation signals. The controller26is not limited to one component and may be divided into a plurality of controllers.

The control valve27is a proportional control valve and is controlled by command signals from the controller26. The control valve27is disposed between the hydraulic pump23and hydraulic actuators such as the lift cylinder19, the angle cylinder20, and the tilt cylinder21. The amount of the operating fluid supplied from the hydraulic pump23to the lift cylinder19, the angle cylinder20, and the tilt cylinder21is controlled by the control valve27. The controller26generates a command signal to the control valve27so that the work implement13acts in accordance with the abovementioned operations of the operating device25. As a result, the lift cylinder19, the angle cylinder20, and the tilt cylinder21and the like are controlled in response to the operation amount of the operating device25. The control valve27may be a pressure proportional control valve. Alternatively, the control valve27may be an electromagnetic proportional control valve.

The control system3is provided with a lift cylinder sensor29. The lift cylinder sensor29detects the stroke length (referred to below as “lift cylinder length L”) of the lift cylinder19. As depicted inFIG. 3, the controller26calculates a lift angle θlift of the blade18on the basis of the lift cylinder length L.FIG. 3is a schematic view of a configuration of the work vehicle1.

The origin position of the work implement13is depicted as a chain double-dashed line inFIG. 3. The origin position of the work implement13is the position of the blade18while the tip of the blade18is in contact with the ground surface on a horizontal ground surface. The lift angle θlift is the angle from the origin position of the work implement13.

As illustrated inFIG. 2, the control system3is provided with a position detection device31. The position detection device31detects the position of the work vehicle1. The position detection device31is provided with a GNSS receiver32and an IMU33. The GNSS receiver32is disposed on the operating cabin14. The GNSS receiver32is, for example, an antenna for a global positioning system (GPS). The GNSS receiver32receives vehicle position information which indicates the position of the work vehicle1. The controller26acquires the vehicle position information from the GNSS receiver32.

The IMU33is an inertial measurement unit. The IMU33acquires vehicle inclination angle information. The vehicle inclination angle information includes the angle (pitch angle) relative to horizontal in the vehicle front-back direction and the angle (roll angle) relative to horizontal in the vehicle lateral direction. The IMU33transmits the vehicle inclination angle information to the controller26. The controller26acquires the vehicle inclination angle information from the IMU33.

The controller26computes a blade tip position P1from the lift cylinder length L, the vehicle position information, and the vehicle inclination angle information. As illustrated inFIG. 3, the controller26calculates global coordinates of the GNSS receiver32on the basis of the vehicle position information. The controller26calculates the lift angle θlift on the basis of the lift cylinder length L. The controller26calculates local coordinates of the blade tip position P1with respect to the GNSS receiver32on the basis of the lift angle θlift and vehicle dimension information. The vehicle dimension information is stored in the storage device28and indicates the position of the work implement13with respect to the GNSS receiver32. The controller26calculates the global coordinates of the blade tip position P1on the basis of the global coordinates of the GNSS receiver32, the local coordinates of the blade tip position P1, and the vehicle inclination angle information. The controller26acquires the global coordinates of the blade tip position P1as blade tip position information.

As illustrated inFIG. 2, the control system3is provided with a soil amount acquisition device34. The soil amount acquisition device34acquires soil amount information which indicates the amount of soil held by the work implement13. The soil amount acquisition device34generates a soil amount signal which indicates the soil amount information and sends the soil amount signal to the controller26. In the present embodiment, the soil amount information indicates the tractive force of the work vehicle1. The controller26calculates the held soil amount from the tractive force of the work vehicle1. For example, in the work vehicle1provided with the HST, the soil amount acquisition device34is a sensor for detecting the hydraulic pressure (driving hydraulic pressure) supplied to the hydraulic motor of the HST. In this case, the controller26calculates the tractive force from the driving hydraulic pressure and calculates the held soil amount from the calculated tractive force.

Alternatively, the soil amount acquisition device34may be a survey device that detects changes in the actual topography. In this case, the controller26may calculate the held soil amount from a change in the actual topography. Alternatively, the soil amount acquisition device34may be a camera that acquires image information of the soil carried by the work implement13. In this case, the controller26may calculate the held soil amount from the image information.

The control system3is provided with a storage device28. The storage device28includes, for example, a memory and an auxiliary storage device. The storage device28may be a RAM or a ROM, for example. The storage device28may be a semiconductor memory or a hard disk and the like.

The storage device28stores design topography information. The design topography information indicates the position and the shape of a final design topography. The final design topography indicates a target topography of a work target at the work site. The controller26acquires actual topography information. The actual topography information indicates the position and shape of the actual topography of the work target at the work site. The controller26automatically controls the work implement13on the basis of the actual topography information, the design topography information, and the blade tip position information.

Automatic control of the work implement13during filling work and executed by the controller26will be explained below.FIG. 4depicts an example of a final design topography60and an actual topography50positioned below the final design topography60. During filling work, the work vehicle1piles up and compacts the soil on top of the actual topography50positioned below the final design topography60, whereby the work target is formed so as to become the final design topography60.

The controller26acquires actual topography information which indicates the actual topography50. For example, the controller26acquires position information which indicates the locus of the blade tip position P1as the actual topography information. Therefore, the position detection device31functions as an actual topography acquisition device for acquiring the actual topography information.

Alternatively, the controller26may calculate the position of the bottom surface of the crawler belt16from the vehicle position information and the vehicle dimension information, and may acquire the position information which indicates the locus of the bottom surface of the crawler belt16as the actual topography information. Alternatively, the actual topography information may be generated from survey data measured by a survey device outside of the work vehicle1. Alternatively, the actual topography50may be imaged by a camera and the actual topography information may be generated from image data acquired by the camera.

As illustrated inFIG. 4, the final design topography60is horizontal and flat in the present embodiment. However, a portion or all of the final design topography60may be inclined. InFIG. 4, the height of the final design topography in the range from −d2to 0 is the same as the height of the actual topography50.

The controller26determines an intermediate design topography70that is positioned between the actual topography50and the final design topography60. InFIG. 4, a plurality of the intermediate design topographies70are indicated by dashed lines; however, only a portion thereof is given the reference numeral “70.” As illustrated inFIG. 4, the intermediate design topography70is positioned above the actual topography50and below the final design topography60. The controller26determines the intermediate design topography70on the basis of the actual topography information, the design topography information, and the soil amount information.

The intermediate design topography70is set to the position of a predetermined distance D1above the actual topography50. The controller26determines the next intermediate design topography70at the position of the predetermined distance D1above the updated actual topography50each time the actual topography50is updated. As a result, the plurality of intermediate design topographies70which are stacked on the actual topography50are generated as illustrated inFIG. 4. The processing for determining the intermediate design topography70is explained in detail below.

The controller26controls the work implement13on the basis of intermediate topography information which indicates the intermediate design topography70and blade tip position information which indicates the blade tip position P1. Specifically, the controller26generates command signals for the work implement13so as to move the blade tip position P1of the work implement13along the intermediate design topography70.

FIG. 5is a flow chart depicting automatic control processing of the work implement13during filling work. As illustrated inFIG. 5, the controller26acquires the current position information in step S101. As illustrated inFIG. 6, the controller26acquires the height Hm_−1 of an intermediate design surface70_−1 that is one position before the previously determined reference position P0, and a pitch angle θm_−1 of the intermediate design surface70_−1.

However, during the initial state of the filling work, the controller26acquires the actual surface50_−1 which is one surface before the reference position P0in place of the height Hm_−1 of the intermediate design topography70_−1 that is one position before the previously determined reference position P0. During the initial state of the filling work, the controller26acquires the pitch angle of the actual surface50_−1 which is one surface before the reference position P0in place of the pitch angle θm_−1 of the intermediate design topography70_−1 that is one position before the previously determined reference position P0. The initial state of the filling work can be a state when the work vehicle is switched, for example, from reverse travel to forward travel.

In step S102, the controller26acquires the actual topography information. As illustrated inFIG. 6, the actual topography50includes a plurality of actual surfaces50_1to50_10which are divided by a predetermined interval d1from the predetermined reference position P0in the traveling direction of the work vehicle1. The reference position P0is the position where the actual topography50starts to slope downward from the final design topography60in the traveling direction of the work vehicle1. In other words, the reference position P0is the position where the height of actual topography50starts to become smaller than the height of the final design topography60in the traveling direction of the work vehicle1. Alternatively, the reference position P0is a position in front of the work vehicle1by a predetermined distance. Alternatively, the reference position P0is the current position of the blade tip position P1of the work vehicle1. Alternatively, the reference position P0may be a position at the top of the slope of the actual topography50. InFIG. 6, the vertical axis indicates the height of the topography and the horizontal axis indicates the distance from the reference position P0.

The actual topography information includes the position information of the actual surfaces50_1to50_10for each predetermined interval d1from the reference position P0in the traveling direction of the work vehicle1. That is, the actual topography information includes the position information of the actual surfaces50_1to50_10from the reference position P0as far forward as the predetermined distance d10.

As illustrated inFIG. 6, the controller26acquires the heights Ha_1to Ha_10of the actual surfaces50_1to50_10as the actual topography information. In the present embodiment, the actual surfaces acquired as the actual topography information include up to ten actual surfaces; however, the number of actual surfaces may be more than ten or less than ten.

In step S103, the controller26acquires the design topography information. As illustrated inFIG. 6, the final design topography60includes a plurality of final design surfaces60_1to60_10. Therefore, the design topography information includes the position information of the final design surfaces60_1to60_10at each predetermined interval d1in the traveling direction of the work vehicle1. That is, the design topography information includes the position information of the final design surfaces60_1to60_10from the reference position P0as far forward as the predetermined distance d10.

As illustrated inFIG. 6, the controller26acquires the heights Hf_1to Hf_10of the final design surfaces60_1to60_10as the design topography information. In the present embodiment, the number of final design surfaces acquired as the design topography information includes up to ten final design surfaces; however, the number of final design surfaces may be more than ten or less than ten.

In step S104, the controller26acquires the soil amount information. In this case, the controller26acquires the current held soil amount Vs_0. The held soil amount Vs_0is represented, for example, as a ratio with respect to the capacity of the blade18.

In step S105, the controller26determines the intermediate design topography70. The controller26determines the intermediate design topography70from the actual topography information, the design topography information, the soil amount information, and the current position information. The processing for determining the intermediate design topography70is explained in detail below.

FIG. 7is a flow chart depicting processing for determining the intermediate design topography70. In step S201, the controller26determines a bottom height Hbottom. In this case, the controller26determines the bottom height Hbottom so that the bottom soil amount coincides with the held soil amount.

As illustrated inFIG. 8, the bottom soil amount represents the amount of soil piled below the bottom height Hbottom and above the actual surface50. For example, the controller26calculates the bottom height Hbottom from the product of the total of bottom lengths Lb_4to Lb_10and the predetermined distance d1, and from the held soil amount. The bottom lengths Lb_4to Lb_10represent the distance from the actual topography50upwards to the bottom height Hbottom.

In step S202, the controller26determines a first upper limit height Hup1. The first upper limit height Hup1defines an upper limit of the height of the intermediate design topography70. However, the intermediate design topography70may be determined to be positioned above the first upper limit height Hup1in response to other conditions. The first upper limit height Hup1is defined using the following equation 1.
Hup1=MIN(final design topography,actual topography+D1)  (Equation 1)
Therefore as illustrated inFIG. 9, the first upper limit height Hup1is positioned below the final design topography60and above the actual topography50by a predetermined distance D1. The predetermined distance D1is the thickness of the piled soil to a degree that the piled soil can be appropriately compacted by the work vehicle1traveling one time over the piled soil.

In step S203, the controller26determines a first lower limit height Hlow1. The first lower limit height Hlow1defines a lower limit of the height of the intermediate design topography70. However, the intermediate design topography70may be determined to be positioned below the first lower limit height Hlow1in response to other conditions. The first lower limit height Hlow1is defined using the following equation 2.
Hlow1=MIN(final design topography,MAX(actual topography,bottom))  (Equation 2)
Therefore as illustrated inFIG. 9, when the actual topography50is positioned below the final design topography60and above the abovementioned bottom height Hbottom, the first lower limit height Hlow1coincides with the actual topography50. Additionally, when the bottom height Hbottom is positioned below the final design topography60and above the actual topography50, the first lower limit height Hlow1coincides with the bottom height Hbottom.

In step S204, the controller26determines a second upper limit height Hup2. The second upper limit height Hup2defines an upper limit of the height of the intermediate design topography70. The second upper limit height Hup2is defined using the following equation 3.
Hup2=MIN(final design topography,MAX(actual topography+D2,bottom))  (Equation 3)
Therefore as illustrated inFIG. 9, the second upper limit height Hup2is positioned below the final design topography60and above the actual topography50by a predetermined distance D2. The predetermined distance D2is larger than the predetermined distance D1.

In step S205, the controller26determines a second lower limit height Hlow2. The second lower limit height Hlow2defines a lower limit of the height of the intermediate design topography70. The second lower limit height Hlow2is defined using the following equation 4.
Hlow2=MIN(final design topography−D3,MAX(actual topography−D3,bottom))   (Equation 4)
Therefore as illustrated inFIG. 9, the second lower limit height Hlow2is positioned below the final design topography60by a predetermined distance D3. The second lower limit height Hlow2is positioned below the first lower limit height Hlow1by the predetermined distance D3.

In step S206, the controller26determines the pitch angle of intermediate design topography. As illustrated inFIG. 4, the intermediate design topography70includes the plurality of intermediate design surfaces70_1to70_10, which are connected end-to-end and each configured to span the predetermined interval d1in the traveling direction of the work vehicle. The controller26determines the pitch angle for each of the plurality of intermediate design surfaces70_1to70_10. The intermediate design topography70illustrated inFIG. 4has different pitch angles for the respective intermediate design surfaces70_1to70_4. In this case, the intermediate design topography70has a shape that is bent at a plurality of locations as illustrated inFIG. 4.

FIG. 10is a flow chart depicting processing for determining the pitch angles of the intermediate design topography70. The controller26determines the pitch angle of the intermediate design surface70_1that is one position ahead the reference position P0by using the processing illustrated inFIG. 10.

In step S301, the controller26determines a first upper limit angle θup1as illustrated inFIG. 10. The first upper limit angle θup1defines an upper limit of the pitch angle of the intermediate design topography70. However, the pitch angle of the intermediate design topography70may be larger than the first upper limit angle θup1in response to other conditions.

As illustrated inFIG. 11, the first upper limit angle θup1is the pitch angle of the intermediate design surface70_1so that the intermediate design surface70_1does not exceed the first upper limit height Hup1up to the distance d10when the pitch angle of the intermediate design topography70is set to the degree (previous degree−A1) for each interval d1. The first upper limit angle θup1is determined as indicated below.

When the pitch angle of the intermediate design topography70is set as the degree (previous degree−A1) at each interval d1, the pitch angle θn of the intermediate design surface70_1is determined using the following equation 5 such that the nth ahead intermediate design surface70_nis equal to or less than the first upper limit height Hup1.
θn=(Hup1_n−Hm_−1+A1*(n*(n−1)/2))/n(Equation 5)

Hup1_n(e.g., Hup1_1, Hup1_2, etc.) is the first upper limit height Hup1at the nth ahead intermediate design surface70_n. Hm_−1 is the height of the intermediate design surface70_−1 which is one position behind the reference position P0. A1is a predetermined constant. On values are determined from n=1 to 10 using equation 5, and the minimum θn value is selected as the first upper limit angle θup1. InFIG. 11, the minimum θn value from n=1 to 10 becomes the pitch angle θ2that does not exceed the first upper limit height Hup1at the distance d2in front of the reference position P0. In this case, θ2is selected as the first upper limit angle θup1.

However, when the selected first upper limit angle θup1is larger than a predetermined change upper limit θlimit1, the change upper limit θlimit1is selected as the first upper limit angle θup1. The change upper limit θlimit1is a threshold for limiting the change in the pitch angle from the previous pitch angle to +A1or less.

In the present embodiment, while the pitch angle is determined on the basis of the intermediate design surfaces70_1to70_10as far as ten positions in front of the reference position P0, the number of intermediate design surfaces used in the computation of the pitch angle is not limited to ten and may be more than ten or less than ten.

In step S302, the controller26determines a first lower limit angle θlow1. The first lower limit angle θlow1defines a lower limit of the pitch angle of the intermediate design topography70. However, the pitch angle of the intermediate design topography70may be less than the first lower limit angle θlow1in response to other conditions. As illustrated inFIG. 12, the first lower limit angle θlow1is the pitch angle of the intermediate design surface70_1so that the intermediate design surface70_1does not fall below the first lower limit height Hlow1as far forward as the distance d10when the pitch angle of the intermediate design topography70is set to the degree (previous degree−A1) for each interval d1. The first lower limit angle θlow1is determined as indicated below.

When the pitch angle of the intermediate design topography70is set as the degree (previous degree+A1) at each interval d1, one pitch angle θn in front is determined using the following equation 6 such that the nth ahead intermediate design surface70_nis equal to or greater than the first lower limit height Hlow1.
θn=(Hlow1_n−Hm_−1−A1*(n*(n−1)/2))/n(Equation 6)
Hlow1_nis the first lower limit height Hlow1with respect to the nth ahead intermediate design surface70_n. On values are determined from n=1 to 10 using equation 6, and the maximum of the θn values is selected as the first lower limit angle θlow1. InFIG. 12, the maximum of the θn values from n=1 to 10 becomes the pitch angle θ3that does not exceed the first upper limit height Hup1at the distance d3in front of the reference position P0. In this case, θ3is selected as the first lower limit angle θlow1.

However, when the selected first lower limit angle θlow1is smaller than a predetermined change lower limit θlimit2, the change lower limit θlimit2is selected as the first lower limit angle θlow1. The change lower limit θlimit2is a threshold for limiting a change in the pitch angle from the previous pitch angle to −A1or greater.

In step S303, the controller26determines a second upper limit angle θup2. The second upper limit angle θup2defines an upper limit of the pitch angle of the intermediate design topography70. The second upper limit angle θup2is the pitch angle of the intermediate design surface70_1so that the intermediate design surface70_1does not exceed the second upper limit height Hup2as far forward as the distance d10when the pitch angle of the intermediate design topography70is set to the degree (previous degree−A1) for each interval d1. The second upper limit angle θup2is determined in the same way as the first upper limit angle θup1with the following equation 7.
θn(Hup2_n−Hm_−1+A1*(n*(n−1)/2))/n(Equation 7)
Hup2_nis the second upper limit height Hup2with respect to the nth ahead intermediate design surface70_n. On values are determined from n=1 to 10 using equation 7, and the minimum θn value is selected as the second upper limit angle θup2.

In step S304, the controller26determines a second lower limit angle θlow2. The second lower limit angle θlow2defines a lower limit of the pitch angle of the intermediate design topography70. The second lower limit angle θlow2is the pitch angle of the intermediate design surface one position in front of the reference position P0so as not to fall below the second lower limit height Hlow2second lower limit height Hlow2as far forward as the distance d10when the pitch angle of the intermediate design topography70is set to the degree (previous degree+A2) for each interval d1. The angle A2is larger than the abovementioned angle A1. The second lower limit angle θlow2is defined using the following equation 8 in the same way as the first lower limit angle θlow1.
θn=(Hlow2_n−Hm_−1−A2*(n*(n−1)/2))/n(Equation 8)
Hlow2_nis the second lower limit height Hlow2with respect to the nth ahead intermediate design surface70_n. A2is a predetermined constant. On values are determined from n=1 to 10 using equation 8, and the maximum θn value is selected as the second lower limit angle θlow2.

However, when the selected second lower limit angle θlow2is smaller than a predetermined change lower limit θlimit3, the change lower limit θlimit3is selected as the first lower limit angle θlow1. The change lower limit θlimit3is a threshold for limiting the change in the pitch angle from the previous pitch angle to −A2or greater.

In step S305, the controller26determines a shortest distance angle θs. As illustrated inFIG. 13, the shortest distance angle θs is the pitch angle of the intermediate design topography70that has the shortest intermediate design topography70length between the first upper limit height Hup1and the first lower limit height Hlow1. For example, the shortest distance angle θs is determined using the following equation 9.
θs=MAX(θlow1_1,MIN(θup1_1,MAX(θlow1_2,MIN(θup1_2, . . . MAX(θlow1_n,MIN(θup1_n, . . . MAX(θlow1_10,MIN(θup1_10,θm_−1))) . . . )))  (Equation 9)
As illustrated inFIG. 14, θlow1_n(e.g., θup1_1, θup1_2, . . . θup1_9, etc.) is the pitch angle of a straight line that connects the reference position P0and the nth ahead first lower limit height Hlow1(four in front inFIG. 14). θup1_nis the pitch angle of a straight line that connects the reference position P0and the nth ahead first upper limit height Hup1. θm_−1 is the pitch angle of the intermediate design surface70_−1 which is one position in front of the reference position P0. Equation 9 can be represented as indicated inFIG. 15.

In step S306, the controller26determines whether predetermined pitch angle change conditions are satisfied. The pitch angle change conditions are conditions which indicate that an intermediate design topography70is formed so as to be inclined by an angle −A1or greater. That is, the pitch angle change conditions indicate that a gradually sloped intermediate design topography70has been generated.

Specifically, the pitch angle change condition includes the following first to third change conditions. The first change condition is that the shortest distance angle θs is an angle −A1or greater. The second change condition is that the shortest distance angle θs is greater than θlow1_1. The third change condition is that θlow1_1is an angle −A1or greater. When all of the first to third conditions are satisfied, the controller26determines that the pitch angle change conditions are satisfied.

The routine advances to step S307if the pitch angle change conditions are not satisfied. In step S307, the controller26determines the shortest distance angle θs derived in step S306as a target pitch angle θt.

The routine advances to step S308if the pitch angle change conditions are satisfied. In step S308, the controller26determines θlow1_1as the target pitch angle θt. θlow1_1is the pitch angle that follows the first lower limit height Hlow1.

In step S309, the controller26determines a command pitch angle. The controller26determines a command pitch angle θc using the following equation 10.
θc=MAX(θlow2,MIN(θup2,MAX(θlow1,MIN(θup1,θt))))  (Equation 10)
The command pitch angle determined as indicated above is determined as the pitch angle of the intermediate design surface70_1in step S206inFIG. 7. As a result, the intermediate design topography70is determined in step S105inFIG. 5. That is, the intermediate design surface70_1that fulfills the abovementioned command pitch angle is determined for the intermediate design topography70at the reference position P0.

As illustrated inFIG. 5, the controller26generates a command signal for the work implement13in step S106. In this case, the controller26generates a command signal for the work implement13so as to move the blade tip position P1of the work implement13along the determined intermediate design topography70. In addition, the controller26generates a command signal for the work implement13so that the blade tip position P1of the work implement13does not go above the final design topography60. The generated command signals are input to the control valve27. Consequently, the work implement13is controlled so that the blade tip position P1of the work implement13moves along the intermediate design topography70.

The processing depicted inFIG. 5,FIG. 7andFIG. 10is repeated and the controller26acquires new actual topography information and updates the actual topography information. For example, the controller26may acquire and update the actual topography information in real time. Alternatively, the controller26may acquire and update the actual topography information when a predetermined action is carried out.

The controller26determines the next intermediate design topography70on the basis of the updated actual topography information. The work vehicle1then moves the work implement13along the intermediate design topography70while traveling forward again, and upon reaching a certain position, the work vehicle1travels backward and returns. The work vehicle1repeats the above actions whereby the soil is repeatedly stacked on the actual topography50. Consequently, the actual topography50is gradually piled up and as a result the final design topography60is formed.

The intermediate design topography70is determined as illustrated inFIG. 4as a result of the above processing. Specifically, the intermediate design topography70is determined so as to conform to the following conditions.

(1) The first condition is that the intermediate design topography70is lower than the first upper limit height Hup1. According to the first condition, the intermediate design topography70can be determined that is stacked on the actual topography50with a thickness within the predetermined distance D1as illustrated inFIG. 4. As a result, the stacked thickness of the piled soil can be held to within D1so long as there are no constraints due to other conditions. As a result, the vehicle does not have to repeatedly travel over the piled soil to compact the piled soil. Consequently, work efficiency can be improved.

(2) The second condition is that the intermediate design topography70is higher than the first lower limit height Hlow1. According to the second condition, scraping away of the actual topography50can be suppressed so long as there are no constraints due to other conditions.

(3) The third condition is that the intermediate design topography70approaches the first lower limit height Hlow1while the pitch angle of the intermediate design topography70at each interval d1is limited to be equal to or less than an angle of (previous angle−A1). According to the third condition, the change dθ of the pitch angle in the downward direction can be limited to be equal to or less than the angle A1. As a result, a sudden change in the attitude of the vehicle body can be prevented and the work can be performed at a high speed. As a result, work efficiency can be improved. In particular, the inclination angle of the intermediate design topography70near the top of the slope is gentler and a change of the attitude of the work vehicle1at the top of the slope can be reduced.

(4) The fourth condition is that the pitch angle intermediate design topography70is greater than the first lower limit angle θlow1. According to the fourth condition, the change dθ of the pitch angle in the upward direction can be limited to be equal to or less than the angle A1. As a result, a sudden change in the attitude of the vehicle body11can be prevented and the work can be performed at a high speed. As a result, work efficiency can be improved. In particular, the inclination angle of the intermediate design topography70near the bottom of the slope can be gentler. Furthermore, scraping away of the actual topography50can be suppressed below the first lower limit height Hlow1when the intermediate design topography70is set below the first lower limit height Hlow1due to modification of the pitch angle.

(5) The fifth condition is that the shortest distance angle θs is selected as the pitch angle of the intermediate design topography70when the shortest distance angle θs is greater than the first lower limit angle θlow1. According to the fifth condition, the bending points of the intermediate design topography70can be reduced each time the stacking is repeated, and the maximum inclination angle of the intermediate design topography70can be gentler as illustrated inFIG. 4. As a result, a gradually smoother intermediate design topography can be generated each time stacking is repeated. That is, the intermediate design topography70is generated such that the sloped intermediate design topography70approaches a linear state each time the stacking is repeated.

(6) The sixth condition is that θlow1_1along the first lower limit height Hlow1is selected as the pitch angle of the intermediate design topography70when the pitch angle change conditions are satisfied. After a gently inclined surface at the inclination angle A1is formed in front of the work vehicle1on the actual topography50′ as illustrated inFIG. 4as a result of the fifth condition, the filling of the actual topography50′ at the back of the inclined surface can be prioritized.

(7) The seventh condition is that the bottom height Hbottom is determined so that the bottom soil amount coincides with the held soil amount. According to the seventh condition, the controller26changes the predetermined distance D1from the actual topography50to the intermediate design topography70in response to the held soil amount. The stacking thickness of the piled soil can thereby be modified in response to the held soil amount. As a result, the soil remaining on the blade18can be reduced without using the piled soil.

(8) The eighth condition is that the pitch angle intermediate design topography70is less than the second upper limit angle θup2. According to the eighth condition, the maximum stacked thickness can be suppressed to be equal to or less than D2as illustrated inFIG. 4.

When the actual topography is steep due to the pitch angle of the intermediate design topography70being reduced more than the second upper limit angle θup2, the intermediate design surface70is determined so as to scrape away the top of the slope as illustrated inFIG. 4.

(9) The ninth condition is that the pitch angle intermediate design topography70is greater than the second lower limit angle θlow2. Even if the pitch angle is lowered according to the eighth condition, excessive scraping away of the actual topography50is suppressed due to the ninth condition.

As explained above, according to the control system3of the work vehicle1according to the present embodiment, the work implement13is controlled on the basis of the intermediate design topography70that is positioned below the final design topography60. As a result, soil can be piled thinly on the actual topography50in comparison to a case of moving the work implement13along the final design topography60. Consequently, the piled up soil can be easily compacted by the work vehicle1and the quality of the finish of the work can be improved.

In addition, the inclination angles of at least two intermediate design surfaces differ from each other among the plurality of intermediate design surfaces70_1to70_10. Therefore, an intermediate design topography70that is more gently sloped can be easily generated. As a result, a sudden change in the attitude of the work vehicle1can be suppressed. Consequently, unnecessary speed reduction of the work vehicle1can be suppressed and work efficiency can be improved.

Although the embodiment of the present invention has been described so far, the present invention is not limited to the above embodiment and various modifications may be made within the scope of the invention.

The work vehicle is not limited to a bulldozer, and may be another type of work vehicle such as a wheel loader or the like.

The processing for determining the intermediate design topography is not limited to the processing described above and may be modified. For example, a portion of the aforementioned first to ninth conditions may be modified or omitted. Alternatively, a different condition may be added to the first to ninth conditions. For example,FIG. 16illustrates an intermediate design topography70according to a first modified example. As illustrated inFIG. 16, a layered intermediate design topography70may be generated that follows the actual topography50.

In the above embodiment, the actual topography50is inclined so as to drop downward in the forward direction from the reference position P0. However, the actual topography50may be inclined so as to rise up in the forward direction from the reference position P0. For example,FIG. 17illustrates an intermediate design topography70according to a second modified example. As illustrated inFIG. 17, the actual topography50may be inclined so as to rise up in the forward direction from the reference position P0. In this case as well, the controller may determine the intermediate design topography70to be positioned above the actual topography50and below the final design topography60as illustrated inFIG. 17. As a result, the work implement13is automatically controlled so that the blade tip of the work implement13moves to a position in between the actual topography50and the final design topography60and higher than the actual topography50by the predetermined distance D1.

The controller may have a plurality of controllers separated from each other. For example as illustrated inFIG. 18, the controller may include a first controller (remote controller)261disposed outside of the work vehicle1and a second controller (on-board controller)262mounted on the work vehicle1. The first controller261and the second controller262may be able to communicate wirelessly via communication devices38,39. A portion of the abovementioned functions of the controller26may be executed by the first controller261, and the remaining functions may be executed by the second controller262. For example, the processing for determining a virtual design surface70may be performed by the remote controller261. That is, the processing from steps S101to S105illustrated inFIG. 5may be performed by the first controller261. Additionally, the processing (step S106) to output the command signals to the work implement13may be performed by the second controller262.

The work vehicle may be remotely operated. In this case, a portion of the control system may be disposed outside of the work vehicle. For example, the controller may be disposed outside the work vehicle1. The controller may be disposed inside a control center separated from the work site. The operating devices may also be disposed outside of the work vehicle. In this case, the operating cabin may be omitted from the work vehicle. Alternatively, the operating devices may be omitted. The work vehicle may be operated with only the automatic control by the controller without operations by the operating devices.

The actual topography acquisition device is not limited to the abovementioned position detection device31and may be another device. For example, as illustrated inFIG. 19, the actual topography acquisition device may be an interface device37that receives information from external devices. The interface device37may wirelessly receive actual topography information measured by an external measurement device41. Alternatively, the interface device37may be a recording medium reading device and may receive the actual topography information measured by the external measurement device41via a recording medium.

According to the present invention, there are provided a control system for a work vehicle, a control method, and a work vehicle that enable filling work that is efficient and exhibits a quality finish using automatic controls.