Asphalt finisher

Abstract

An asphalt finisher including a screed to level paving material includes a telescopic screed cylinder to move a side frame by extending and retracting upon supply of hydraulic oil, a switching valve capable of being switched between an open state and a closed state, a sensor to detect information concerning a current position of the side frame, and a controller to control a drive of the switching valve, wherein the controller calculates a side frame target path, which specifies a trajectory of the side frame along the laying direction, calculates an extension and retraction speed of the telescopic screed cylinder based on a deviation between the side frame target path and the current position of the side frame detected by the sensor, and controls the telescopic screed cylinder by switching the switching valve between the open state and the closed state based on the extension and retraction speed.

Description

RELATED APPLICATION

[0001] The present application is based on and claims priority to Japanese patent application no. 2024-227610 filed on December 24, 2024, with the Japan Patent Office, the entire contents of which are hereby incorporated by reference.TECHNICAL FIELD

[0002] The disclosures herein relate to asphalt finishers.BACKGROUND

[0003] In recent years, asphalt finishers have been developed that automatically control a width of a screed according to a road surface on which paving material is leveled. If automatic control of a telescopic screed cylinder is performed at the same extension and retraction speed at which the width of the screed is manually controlled, the extension and retraction speed may be too high. In this case, adjustment accuracy when aligning the width of the screed with a target position may decrease. Conversely, if the extension and retraction speed of the telescopic screed cylinder of the asphalt finisher is reduced in order to increase control accuracy, operation of the asphalt finisher becomes slow when it is manually operated.

[0004] Therefore, it is conceivable to make the extension and retraction speed of the width of the screed variable. For example, a related art discloses an asphalt finisher in which a detection sensor provided on a screed detects a laying boundary relative to a paved surface, and when an outer end of a widener is displaced to one side relative to the laying boundary, displacement is corrected by adjusting the extension and retraction speed of the widener.SUMMARY

[0005] An asphalt finisher including a screed configured to level paving material while moving in a laying direction of the paving material, includes a telescopic screed cylinder configured to move a side frame, which defines a leveling limit of the screed, by extending and retracting upon supply of hydraulic oil, a switching valve capable of being switched between an open state where the hydraulic oil is supplied to the telescopic screed cylinder, and a closed state where supply of the hydraulic oil is stopped, a sensor configured to detect information concerning a current position of the side frame, and a controller configured to control a drive of the switching valve, wherein the controller is configured to calculate a side frame target path, which specifies a trajectory of the side frame along the laying direction, calculate an extension and retraction speed of the telescopic screed cylinder based on a deviation between the side frame target path and the current position of the side frame detected by the sensor, and control the telescopic screed cylinder by switching the switching valve between the open state and the closed state based on the extension and retraction speed.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is a side view illustrating an asphalt finisher according to the present embodiment;

[0007] FIG. 2 is a plan view illustrating the asphalt finisher;

[0008] FIG. 3 is a block diagram illustrating an example configuration of an automatic steering system;

[0009] FIG. 4 is a plan view illustrating a construction site in which the asphalt finisher passes along a straight portion, a curved portion, and another straight portion of a road to be constructed;

[0010] FIG. 5 is a drawing illustrating a hydraulic circuit for a right telescopic screed cylinder;

[0011] FIG. 6A is a drawing illustrating a supply state of hydraulic oil controlled by a switching valve;

[0012] FIG. 6B is a graph illustrating the extension and retraction speed of a telescopic screed cylinder with a duty ratio when hydraulic oil is supplied;

[0013] FIG. 7A is a plan view illustrating an operation of extending a right side frame by the right telescopic screed cylinder;

[0014] FIG. 7B is a drawing illustrating an operation of the switching valve when controlling the extension and retraction speed of the right telescopic screed cylinder;

[0015] FIG. 7C is a drawing illustrating an operation of the switching valve when controlling the extension and retraction speed of a right telescopic screed cylinder according to a modification; and

[0016] FIG. 8 is a flowchart illustrating a method for controlling the telescopic screed cylinder.DETAILED DESCRIPTION

[0017] In a technology described in PTL 1, since displacement is determined by a detection sensor provided on a screed, only a current position of the detection sensor (or its immediate vicinity) can be recognized. In this case, it is difficult to accurately adjust a width of the screed with respect to an actual target position at an appropriate speed.

[0018] The present disclosure provides an asphalt finisher capable of accurately adjusting the width of a screed by extending and retracting a screed extending cylinder at an appropriate extension and retraction speed.

[0019] In the following, an embodiment of the present invention will be described with reference to the accompanying drawings. In the drawings, the same constituent elements are denoted with the same reference numerals, and redundant description thereabout may be omitted.

[0020] FIG. 1 is a side view illustrating an asphalt finisher 100 according to the present embodiment. FIG. 2 is a plan view illustrating the asphalt finisher 100. The asphalt finisher 100 according to the present embodiment is a wheel type asphalt finisher, and mainly includes a tractor 1, a hopper 2, and a screed 3. Hereinafter, a direction of the hopper 2 when viewed from the tractor 1 (+X direction) is referred to as a forward direction, and the direction of the screed 3 when viewed from the tractor 1 (-X direction) is referred to as a rearward direction.

[0021] The tractor 1 is a mechanism for moving the asphalt finisher 100. The tractor 1 moves the asphalt finisher 100 by rotating rear wheels 5 using a hydraulic drive motor for rear wheels and rotating front wheels 6 using a hydraulic drive motor for front wheels. The hydraulic drive motor for rear wheels and the hydraulic drive motor for front wheels are rotated by receiving hydraulic oil from a hydraulic pump. One of the rear wheels 5 and the front wheels 6 may be a driven wheel. The asphalt finisher 100 may be a crawler-type asphalt finisher in which the rear wheels 5 and the front wheels 6 are replaced with a left crawler and a right crawler.

[0022] The asphalt finisher 100 includes a controller 50 that is a control part for controlling various configurations. The controller 50 is, for example, a microcomputer including a processor, a memory (volatile storage device, non-volatile storage device, and the like), and an input and output interface, and is mounted on the tractor 1. Each function of the controller 50 is achieved by the processor executing a program stored in a nonvolatile storage device. However, each function of the controller 50 may be achieved not only by software but also by hardware or a combination of hardware and software.

[0023] The hopper 2 is a mechanism for receiving paving material. In the illustrated example, the hopper 2 is installed on the front side of the tractor 1 and is opened and closed in a vehicle width direction (Y-axis direction) by a hopper cylinder. The asphalt finisher 100 usually receives paving material (e.g., asphalt mixture) from a dump body of a dump truck when the hopper 2 is in a fully opened state. A dump truck is an example of a carrying vehicle for carrying the paving material. FIGS. 1 and 2 illustrate the fully opened state of the hopper 2. When the paving material in the hopper 2 decreases, the hopper 2 is closed, and the paving material near the inner wall of the hopper 2 is collected in the central part of the hopper 2. This is so that a conveyor CV in the central part of the hopper 2 can feed the paving material to the rear side of the tractor 1. The paving material fed to the rear side of the tractor 1 is spread in the vehicle width direction on the rear side of the tractor 1 and the front side of the screed 3 by a screw SC. In the illustrated example, the screw SC is in a state in which the extension screw is connected to the right and left sides. In FIGS. 1 and 2, for ease of understanding, the paving material in the hopper 2 is not shown, and the paving material PV spread by the screw SC is shown in a coarse dot pattern, and newly constructed pavement NP leveled by the screed 3 is shown in a fine dot pattern.

[0024] The screed 3 is a mechanism for leveling the paving material PV. The screed 3 according to the embodiment includes a front screed 30 and a rear screed 31. The front screed 30 includes a left front screed 30L and a right front screed 30R. The rear screed 31 is a screed extendable in the vehicle width direction and includes a left rear screed 31L and a right rear screed 31R. The rear screed 31 is extendable in the vehicle width direction by a telescopic screed cylinder 26. Specifically, the left rear screed 31L is extendable in the vehicle width direction by using the left telescopic screed cylinder 26L. The right rear screed 31R is extendable in the vehicle width direction by using the right telescopic screed cylinder 26R. The screed 3 is a floating screed pulled by the tractor 1 and is connected to the tractor 1 via a leveling arm 3A. The leveling arm 3A includes a left leveling arm 3AL arranged on the left side of the tractor 1 and a right leveling arm 3AR arranged on the right side of the tractor 1.

[0025] A mold board 43 is attached to the front part of the screed 3. The mold board 43 adjusts an amount of the paving material PV staying in front of the screed 3. The paving material PV reaches below the screed 3 through a gap between the lower end of the mold board 43 and a roadbed BS.

[0026] A pair of side frames 32 (left side frame 32L and right side frame 32R) for regulating the leveling limit of the paving material PV are attached to both ends in the width direction of the rear screed 31. The left side frame 32L extends at a predetermined length in a front-rear direction at the left end of the rear screed 31. The left side frame 32L is displaced in the vehicle width direction by extension and retraction of the left telescopic screed cylinder 26L. The right side frame 32R extends at a predetermined length in the front-rear direction at the right end of the rear screed 31. The right side frame 32R is displaced in the vehicle width direction by extension and retraction of the right telescopic screed cylinder 26R.

[0027] An information acquisition device 51, a vehicle-mounted display device 52, a steering device 53, and a screed extension and retraction control device 54 are attached to the tractor 1.

[0028] The information acquisition device 51 acquires information about the road to be constructed, and outputs the acquired information to the controller 50. The information about the road to be constructed includes, for example, a width of the road, a change in curvature in a gradual-change section (clothoid section), and a curvature in an arc section. The information acquisition device 51 includes, for example, a front monitoring device 51F, a rear monitoring device 51B, a travel speed sensor 51S, a positioning device 51P, and a communication device 51T.

[0029] The front monitoring device 51F acquires information about an external environment in front of the asphalt finisher 100. A camera for monitoring a monitoring range RF in front of the tractor 1 or a LiDAR can be applied to the front monitoring device 51F. The front monitoring device 51F is attached to the central part (e.g., the central part of the front end of a cover for an engine compartment provided on the rear side of the hopper 2) of the tractor 1. However, the front monitoring device 51F may be attached to another part of the asphalt finisher 100. The front monitoring device 51F may include a combination of a plurality of cameras and a plurality of LiDARs. For example, the LiDARs may include a right front LiDAR attached to the right part of the front end of the tractor 1 and a left front LiDAR attached to the left part of the front end of the tractor 1.

[0030] The rear monitoring device 51B acquires information about the external environment behind the asphalt finisher 100. The rear monitoring device 51B may employ a camera or LiDAR for monitoring the monitoring range RB behind the screed 3. The rear monitoring device 51B is attached to a guide rail 1G functioning as a handrail. However, the rear monitoring device 51B may be attached to a lower part of an operator’s seat 1S or to another part of the asphalt finisher 100. Further, the rear monitoring device 51B may be constituted by combining a plurality of cameras and a plurality of LiDARs. For example, the plurality of LiDARs may include a right rear LiDAR attached to the right part of the rear end of the tractor 1 and a left rear LiDAR attached to the left part of the rear end of the tractor 1.

[0031] Further, the information acquisition device 51 may include lateral monitoring devices for monitoring the lateral direction of the asphalt finisher 100. In this case, the lateral monitoring devices include a left lateral monitoring device and a right lateral monitoring device. The left lateral monitoring device is, for example, a camera or LiDAR for monitoring a monitoring range on the left of the tractor 1 and is attached to the left end of the upper surface of the tractor 1. The right lateral monitoring device is, for example, a camera or LiDAR for monitoring a monitoring range on the right of the tractor 1 and is attached to the right end of the upper surface of the tractor 1.

[0032] The camera may be either a monocular camera or a stereo camera, and captures an image of the surroundings to acquire imaging information. The LiDAR measures, for example, a distance between a number of points in the monitoring range and the LiDAR. However, one or both of the front monitoring device 51F and the rear monitoring device 51B are not limited to a camera or a LiDAR, and may be a millimeter-wave radar, a laser radar, a laser scanner, a range image camera, a laser rangefinder, or the like. The same applies to the lateral monitoring device.

[0033] The front monitoring device 51F is desirably configured to be able to detect the monitoring range RF including the roadbed BS and a feature AP outside the roadbed BS. This is for acquiring information about the width of the road to be constructed. The same applies to the monitoring range of the lateral monitoring device. In the illustrated example, the monitoring range RF has a width larger than the width of the roadbed BS. The feature AP is, for example, a pavement form, an L-shaped gutter block, a curb block, or an existing pavement.

[0034] The rear monitoring device 51B is desirably configured to be able to detect the monitoring range RB including the newly constructed pavement NP and the feature AP located outside the newly constructed pavement NP. This is so that information on the width of the newly constructed pavement NP can be acquired. In the illustrated example, the monitoring range RB has a width larger than the width of the newly constructed pavement NP.

[0035] The travel speed sensor 51S detects the travel speed of the asphalt finisher 100. For example, the travel speed sensor 51S is a wheel speed sensor configured to detect angular speed and angle of rotation of the rear wheel 5, so that the travel speed and traveling distance of the asphalt finisher 100 can be determined.

[0036] The positioning device 51P is configured to measure a position of the asphalt finisher 100. For example, the positioning device 51P is a GNSS compass and is configured to measure the position and attitude of the asphalt finisher 100. The GNSS compass as the positioning device 51P includes a left GNSS receiver 51PL attached to a pole PL at the rear end of the left leveling arm 3AL and a right GNSS receiver 51PR attached to the pole PL at the rear end of the right leveling arm 3AR.

[0037] Note that the positioning device 51P may be a total station. In this case, a reflecting prism serving as a target of the total station is attached to the tip of the pole PL. The main body of the total station installed around the asphalt finisher 100 is connected to the controller 50 via wireless communication. That is, the main body of the total station transmits information about the position of the derived target to the controller 50.

[0038] The communication device 51T performs information communication between the asphalt finisher 100 and equipment outside the asphalt finisher 100. In the illustrated example, the communication device 51T is installed in front of the operator’s seat 1S and is configured to execute communication via a mobile communication network, a short-range wireless communication network, a satellite communication network, or the like.

[0039] Further, the information acquisition device 51 may include a steering angle sensor 51R (see FIG. 3) for detecting the steering angle of the asphalt finisher 100 and a screed position sensor 51C (see FIG. 3) for calculating the position of the side frame 32.

[0040] Further, the information acquisition device 51 may include a monitoring device installed at a construction site or a monitoring device attached to a flying vehicle flying over the asphalt finisher 100. The monitoring device installed at the construction site is, for example, a camera, LiDAR, or the like installed at the tip of a pole installed along the road to be constructed. The monitoring device installed on the flying object is, for example, a camera, LiDAR, or the like installed on a multicopter (drone) or an airship.

[0041] The vehicle-mounted display device 52 displays information about the asphalt finisher 100. The vehicle-mounted display device 52 according to the present embodiment is a liquid crystal display installed in front of the operator’s seat 1S. However, the vehicle-mounted display device 52 may be installed at the left end or the right end of the screed 3.

[0042] The steering device 53 is a device for steering the asphalt finisher 100. The steering device 53 according to the embodiment extends and retracts a front wheel steering cylinder installed near the front axle. Specifically, the steering device 53 includes a steering electromagnetic control valve for controlling a flow rate of the hydraulic oil flowing from the hydraulic pump to the front wheel steering cylinder and the flow rate of the hydraulic oil discharged from the front wheel steering cylinder. The steering electromagnetic control valve controls the flow in and out of the hydraulic oil in the front wheel steering cylinder in accordance with rotation of a steering wheel SH which is an operating device. The steering electromagnetic control valve is configured to control the flow in and out of the hydraulic oil in the front wheel steering cylinder in accordance with a control command from the controller 50, independently of the rotation of the steering wheel SH. That is, the controller 50 can automatically control the steering of the asphalt finisher 100 independently of whether or not the steering wheel SH is operated by an operator.

[0043] When the asphalt finisher 100 is a crawler type asphalt finisher, the steering device 53 is configured to separately control a pair of left and right crawlers. Specifically, the steering device 53 includes a left electromagnetic control valve for controlling the flow rate of the hydraulic oil flowing from the hydraulic pump to the left traveling hydraulic motor for rotating the left crawler, and a right electromagnetic control valve for controlling the flow rate of the hydraulic oil flowing from the hydraulic pump to the right traveling hydraulic motor for rotating the right crawler. The left electromagnetic control valve controls the flow in and out of the hydraulic oil in the left traveling hydraulic motor in accordance with an operation amount (inclination angle) of a left operation lever, which is an operation device for operating the left crawler. The left electromagnetic control valve is configured to control the flow in and out of the hydraulic oil in the left traveling hydraulic motor in response to a control command from the controller 50, regardless of whether or not the operator operates the left operation lever. Similarly, the right electromagnetic control valve controls the flow in and out of the hydraulic oil in the right traveling hydraulic motor in accordance with an operation amount (inclination angle) of a right operation lever, which is an operation device for operating the right crawler. The right electromagnetic control valve is configured to control the flow in and out of the hydraulic oil in the right traveling hydraulic motor in response to a control command from the controller 50, regardless of whether or not the operator operates the right operation lever.

[0044] The screed extension and retraction control device 54 controls the telescopic screed cylinder 26 to extend and retract the rear screed 31. Specifically, the screed 3 includes a control valve unit 33 for controlling the flow rate of the hydraulic oil flowing from the hydraulic pump to the telescopic screed cylinder 26 and the flow rate of the hydraulic oil discharged from the telescopic screed cylinder 26. The screed extension and retraction control device 54 controls the drive of the control valve unit 33.

[0045] The screed extension and retraction control device 54 controls the flow of hydraulic oil into and out of the telescopic screed cylinder 26 according to ON and OFF operations of a screed extension and retraction switch (not shown) serving as an operating device. The screed extension and retraction control device 54 is configured to control the flow in and out of the hydraulic oil to and from the telescopic screed cylinder 26 in response to a control command from the controller 50, independently of the operation of the screed extension and retraction switch. That is, the controller 50 can automatically control the extension and retraction amount of the rear screed 31 independently of the operation of the screed extension and retraction switch by the operator. The control of the telescopic screed cylinder 26 will be described later in detail.

[0046] The control valve unit 33 includes a left control valve unit 33L and a right control valve unit 33R and separately controls extension and retraction of the left rear screed 31L and the right rear screed 31R under the control of the screed extension and retraction control device 54. Specifically, the left control valve unit 33L controls flow of hydraulic oil into and out of the left telescopic screed cylinder 26L from and to the hydraulic pump in response to the operation of a left screed extension and retraction switch (not shown) serving as an operating device. The left control valve unit 33L controls flow of hydraulic oil into and out of the left telescopic screed cylinder 26L from and to the hydraulic pump in response to a control command from the controller 50, regardless of whether or not the left screed extension and retraction switch is operated. The same applies to the right electromagnetic control valve.

[0047] Next, a configuration example of the automatic steering system DS mounted on the asphalt finisher 100 will be described with reference to FIG. 3. FIG. 3 is a block diagram illustrating an example configuration of the automatic steering system DS.

[0048] The automatic steering system DS mainly includes the controller 50, the front monitoring device 51F, the rear monitoring device 51B, the travel speed sensor 51S, the positioning device 51P, the steering angle sensor 51R, the screed position sensor 51C, the communication device 51T, the vehicle-mounted display device 52, the steering device 53, the screed extension and retraction control device 54, and the like.

[0049] In the example shown in FIG. 3, the controller 50 includes a target calculation part 50a, a steering control part 50b, a side frame target path calculation part 50c, and a screed control part 50d as functional blocks.

[0050] The target calculation part 50a calculates a target used by the steering control part 50b. The target used by the steering control part 50b is, for example, a main target path to be followed by a predetermined point of the asphalt finisher 100. Technically, the target path is a two-dimensional array of a number of target positions. Alternatively, the target used by the steering control part 50b may be a target position to be reached by a predetermined point of the asphalt finisher 100 after an elapse of a predetermined time. The predetermined time is, for example, several hundred milliseconds, several tens of milliseconds, several milliseconds, or several seconds.

[0051] The predetermined point of the asphalt finisher 100 is located on a front-rear axis of the tractor 1 and is preferably set to be located forward of the screed 3. For example, the predetermined point is set at the central part, the central part of the front end, or the central part of the rear end of the tractor 1, the hopper 2, or the screed 3. The asphalt finisher 100 according to the present embodiment sets a predetermined point at the center in the width direction of the screed 3 (front screed 30).

[0052] The target calculation part 50a calculates a main target path to be followed by the predetermined point of the screed 3 based on information about the road to be constructed such as construction data (design data), for example. The main target path is typically calculated before the asphalt finisher 100 starts traveling. Therefore, the main target path may be calculated by a server or the like installed in a management center outside the asphalt finisher 100 and then transmitted to the controller 50 via communication.

[0053] The target calculation part 50a may calculate a main target position as a point to be reached by the predetermined point of the screed 3 after the elapse of a predetermined time. In this case, the main target position is repeatedly calculated at a predetermined control cycle while the asphalt finisher 100 is traveling. For example, when the asphalt finisher 100 is traveling on a straight portion of the road to be constructed, the target calculation part 50a may calculate a center point in the width direction of the road to be constructed located forward by a predetermined distance from the current position of the predetermined point of the screed 3 as the main target position based on information acquired by the front monitoring device 51F. The predetermined distance is, for example, several centimeters to several tens of centimeters. The target calculation part 50a can calculate the main target position without acquiring design data. However, the target calculation part 50a may calculate the main target position based on the design data and information acquired by the front monitoring device 51F. For example, the target calculation part 50a may correct the main target position calculated based on the design data based on information acquired by the front monitoring device 51F. Further, the target calculation part 50a may correct the main target position using information acquired by the rear monitoring device 51B.

[0054] The steering control part 50b automatically controls the steering of the asphalt finisher 100 as an operation support of the operator.

[0055] The steering control part 50b outputs a control command to the steering device 53 so that the set predetermined point of the screed 3 follows the main target path calculated by the target calculation part 50a. Specifically, the steering control part 50b calculates the current position of the predetermined point of the screed 3 based on the output of the positioning device 51P. Then, for example, when it is determined that the predetermined point deviates rightward from the main target path, the steering control part 50b outputs a control command to the steering device 53 so that the tractor 1 moves leftward. Similarly, when it is determined that the predetermined point deviates leftward from the main target path, the steering control part 50b outputs a control command to the steering device 53 so that the asphalt finisher 100 moves rightward.

[0056] Alternatively, the steering control part 50b may output a control command to the steering device 53 so that the predetermined point of the screed 3 aligns with the target position calculated by the target calculation part 50a. In this case, the steering control part 50b may derive the current position of the predetermined point of the screed 3 based on the output of the positioning device 51P or may derive the current position of the predetermined point of the screed 3 based on the output of at least one of the rear monitoring device 51B and the front monitoring device 51F.

[0057] Next, a function for moving the asphalt finisher 100 along the target path will be described with reference to FIG. 4. FIG. 4 is a plan view illustrating a construction site in which the asphalt finisher 100 passes along a straight portion SP1, a curved portion LC (left curve), and another straight portion SP2 of a road RD to be constructed. In FIG. 4, the asphalt finisher 100 at a first point in time, which is a time when construction is started, is indicated by reference numeral 100a. The asphalt finisher 100 at a second point in time, after a predetermined time elapses from the first point in time, is indicated by reference numeral 100b. Similarly, the asphalt finisher 100 at a third point in time, after a predetermined time elapses from the second point in time, is indicated by reference numeral 100c, the asphalt finisher 100 at a fourth point in time, after a predetermined time elapses from the third point in time, is indicated by reference numeral 100d, and the asphalt finisher 100 at a fifth point in time, after a predetermined time elapses from the fourth point in time, is indicated by reference numeral 100e. For the sake of clarity, FIG. 4 shows the tractor 1, the front screed 30, the left rear screed 31L, and the right rear screed 31R of the asphalt finisher 100 in a simplified manner.

[0058] The target calculation part 50a of the controller 50 calculates the main target path TPS to be followed by a predetermined point Q of the screed 3 at the first point in time at the start of construction. In FIG. 4, the predetermined point Q is represented by a triangle, and the main target path TPS is represented by an alternate long and short dash line. For example, the target calculation part 50a derives the main target path TPS based on the left boundary line and the right boundary line of the road RD to be executed with reference to the design data. In FIG. 4, a center line CP of the road RD is shown by a broken line. The main target path TPS may be generated based on a line that divides the area of the road surface leveled by the screed 3 into equal parts on the left and right sides. The area of the road surface is, for example, the area of the road surface leveled when the asphalt finisher 100 advances by a predetermined distance.

[0059] The steering control part 50b of the controller 50 calculates the current position of the predetermined point Q of the screed 3 based on the output of the positioning device 51P. Then, the steering control part 50b operates the asphalt finisher 100 so that the actual position coordinates of the predetermined point Q coincide with one of the position coordinates constituting the main target path TPS. Thus, the steering control part 50b moves the predetermined point Q located at a point Qa at the first point in time to a point Qb at the second point in time, to a point Qc at the third point in time, to a point Qd at the fourth point in time, and to a point Qe at the fifth point in time.

[0060] In the movement of the asphalt finisher 100, the position of the left side frame 32L at the left end portion of the left rear screed 31L is controlled so as to follow the left side frame target path LTP calculated by the controller 50. Similarly, the position of the right side frame 32R at the right end portion of the right rear screed 31R is controlled so as to follow the right side frame target path RTP calculated by the controller 50.

[0061] Therefore, the side frame target path calculation part 50c of the controller 50 shown in FIG. 3 calculates the left side frame target path LTP and the right side frame target path RTP even when the tractor 1 is moved forward so that the predetermined point Q follows the main target path TPS. The left side frame target path LTP is basically calculated as a line corresponding to the left boundary line of the road RD. However, the left side frame target path LTP can be calculated on a line different from the left boundary line depending on capabilities (e.g., the extension and retraction limit and the extension and retraction speed of the screed 3) of the asphalt finisher 100. Similarly, the right side frame target path RTP is basically calculated as a line corresponding to the right boundary line of the road RD. However, the right side frame target path RTP can also be calculated on a line different from the right boundary line according to the capabilities (e.g., the extension and retraction limit and the extension and retraction speed of the screed 3) of the asphalt finisher 100.

[0062] For example, the side frame target path calculation part 50c can calculate the left side frame target path LTP and the right side frame target path RTP based on the construction data acquired in advance and the position of the asphalt finisher 100 determined by the positioning device 51P. In this case, the side frame target path calculation part 50c may calculate the left side frame target path LTP and the right side frame target path RTP before construction. The side frame target path calculation part 50c may also calculate the left side frame target path LTP and the right side frame target path RTP based on detection information detected by the front monitoring device 51F or the lateral monitoring device during construction. For example, the left side frame target path LTP and the right side frame target path RTP are calculated based on information acquired by detecting the left boundary line and the right boundary line several meters ahead of the asphalt finisher 100 by the front monitoring device 51F. Alternatively, the side frame target path calculation part 50c may calculate the left side frame target path LTP and the right side frame target path RTP using construction data, the position of the asphalt finisher 100, and detection information detected by the front monitoring device 51F or the lateral monitoring device.

[0063] The screed control part 50d of the controller 50 outputs a control command to the screed extension and retraction control device 54 based on the left side frame target path LTP and the right side frame target path RTP calculated by the side frame target path calculation part 50c to control the operation of the screed 3. The screed control part 50d outputs a control command so that the left side frame 32L of the left rear screed 31L coincides with the left side frame target path LTP and the right side frame 32R of the right rear screed 31R coincides with the right side frame target path RTP.

[0064] For example, when the left side frame 32L may deviate inward from the left side frame target path LTP, the left side frame 32L is extended to the left. Conversely, when the left side frame 32L may deviate outward from the left side frame target path LTP, the left side frame 32L is shortened to the right. Alternatively, when the right side frame 32R may deviate inward from the right side frame target path RTP, the right side frame 32R is extended to the right. Conversely, when the right side frame 32R may deviate outward from the right side frame target path RTP, the right side frame 32R is shortened to the left. Thus, the construction is performed so that the side frame target path (left side frame target path LTP, right side frame target path RTP) and the width of the newly constructed pavement NP (width of the screed 3) coincide with each other.

[0065] Next, a specific configuration of the control valve unit 33 will be described. FIG. 5 is a drawing illustrating a hydraulic circuit for a right telescopic screed cylinder 26R. Hereinafter, as shown in FIG. 5, the right control valve unit 33R for displacing the position of the right side frame 32R will be described as an example, and a description of the left control valve unit 33L configured similarly to the right control valve unit 33R will be omitted.

[0066] The right control valve unit 33R is installed between a hydraulic pump 25 connected to a hydraulic oil storage tank 24 and a right telescopic screed cylinder 26R. The right control valve unit 33R is connected to a tank 27 for recovering hydraulic oil discharged from the right telescopic screed cylinder 26R. The right control valve unit 33R is provided internally with a switching valve 34 and a check valve 35.

[0067] The right telescopic screed cylinder 26R is provided with a piston rod 262 for dividing the internal space of a cylinder body 261 into a base-side oil chamber 261a and a rod-side oil chamber 261b. The right rear screed 31R (see FIG. 2) is connected to the piston rod 262. The right telescopic screed cylinder 26R extends the piston rod 262 in a distal end direction by supplying hydraulic oil from the right control valve unit 33R to the base-side oil chamber 261a. As a result, the right side frame 32R of the right rear screed 31R is displaced toward the outside in the width direction of the screed 3. Conversely, the right telescopic screed cylinder 26R shortens the piston rod 262 in the base-side direction by supplying hydraulic oil from the right control valve unit 33R to the rod-side oil chamber 261b. As a result, the right side frame 32R of the right rear screed 31R is displaced toward the inner side in the width direction of the screed 3.

[0068] The switching valve 34 of the right control valve unit 33R has a function of selectively supplying the hydraulic oil to the base-side oil chamber 261a and the rod-side oil chamber 261b of the right telescopic screed cylinder 26R and a function of stopping the supply of the hydraulic oil. One end of the switching valve 34 is connected to the hydraulic pump 25 via a supply line 251 and to the tank 27 via a discharge line 271. The other end of the switching valve 34 is connected to the first check valve 351 of the check valve 35 via a first line 346, and connected to the second check valve 352 via a second line 347.

[0069] The supply line 251, the discharge line 271, the first line 346, and the second line 347 are connected together to the main body of the switching valve 34 so as to communicate with three switching paths based on the position of a spool 341 advancing and retreating in the main body. The three switching paths include a supply stopping part 343 for stopping supply of hydraulic oil to the right telescopic screed cylinder 26R, a base-side supply part 344 for supplying the hydraulic oil to the base-side oil chamber 261a of the right telescopic screed cylinder 26R, and a rod-side supply part 345 for supplying the hydraulic oil to the rod-side oil chamber 261b of the right telescopic screed cylinder 26R.

[0070] The supply stopping part 343 has an internal path for shutting off the supply line 251 and connecting the first line 346 and the second line 347 to the discharge line 271. When the spool 341 is disposed in the supply stopping part 343 by driving an electromagnetic coil 342, the switching valve 34 stops the supply of the hydraulic oil from the hydraulic pump 25 and allows excess pressure in the hydraulic oil to be relieved through the first line 346 and the second line 347. Thus, the supply of the hydraulic oil to the right telescopic screed cylinder 26R is stopped and the position of the piston rod 262 can be maintained.

[0071] The base-side supply part 344 has an internal path connecting the supply line 251 to the first line 346 and connecting the discharge line 271 to the second line 347. When the spool 341 is disposed in the base-side supply part 344 by driving the electromagnetic coil 342, the switching valve 34 can supply the hydraulic oil from the hydraulic pump 25 to the base-side oil chamber 261a and discharge the hydraulic oil from the rod-side oil chamber 261b to the tank 27. Thus, the piston rod 262 of the right telescopic screed cylinder 26R is extended.

[0072] The rod-side supply part 345 has an internal path connecting the supply line 251 to the second line 347 and connecting the discharge line 271 to the first line 346. When the spool 341 is disposed in the rod-side supply part 345 by driving the electromagnetic coil 342, the switching valve 34 can supply the hydraulic oil from the hydraulic pump 25 to the rod-side oil chamber 261b and discharge the hydraulic oil from the base-side oil chamber 261a to the tank 27. Thus, the piston rod 262 of the right telescopic screed cylinder 26R is shortened.

[0073] The electromagnetic coil 342 of the switching valve 34 is connected to the screed extension and retraction control device 54 and moves the spool 341 based on power supplied from the screed extension and retraction control device 54. For example, the switching valve 34 can switch between supplying (open state) and stopping (closed state) the hydraulic oil to the base-side oil chamber 261a of the right telescopic screed cylinder 26R by moving the spool 341 between the supply stopping part 343 and the base-side supply part 344. Further, for example, the switching valve 34 can switch between supplying (open state) and stopping (closed state) the hydraulic oil to the rod-side oil chamber 261b of the right telescopic screed cylinder 26R by moving the spool 341 between the supply stopping part 343 and the rod-side supply part 345.

[0074] In controlling the telescopic screed cylinder 26, the screed extension and retraction control device 54 performs PWM (Pulse Width Modulation) control for switching between supplying (open state) and stopping (closed state) the hydraulic oil by the switching valve 34 at regular intervals. Thus, the switching valve 34 adjusts the flow rate of the hydraulic oil to the right telescopic screed cylinder 26R, and the extension and retraction speed of the right telescopic screed cylinder 26R can be adjusted.

[0075] FIG. 6A is a drawing illustrating a supply state of hydraulic oil controlled by the switching valve 34. FIG. 6B is a graph illustrating the extension and retraction speed of the telescopic screed cylinder 26 with a duty ratio when hydraulic oil is supplied. In the PWM control, the screed extension and retraction control device 54 changes the duty ratio, which is the ratio of the time width in the open state to the time width in one cycle based on the target extension and retraction speed of the right telescopic screed cylinder 26R.

[0076] Here, as shown in FIG. 6B, when the duty ratio is 100%, the switching valve 34 is always in the open state. In this case, the switching valve 34 continues in the open state, and the flow rate of the hydraulic oil is supplied to the right telescopic screed cylinder 26R in a maximum state. Therefore, the extension and retraction speed of the right telescopic screed cylinder 26R becomes constant at the limit value when the duty ratio is 100%.

[0077] As shown in FIG. 6A, when the duty ratio is less than 100%, the switching valve 34 repeatedly switches between the open state and the closed state to reduce the flow rate of the hydraulic oil as compared with the case where the duty ratio is 100%. This slows the extension and retraction speed of the telescopic screed cylinder 26. Further, as the duty ratio decreases, the flow rate of the hydraulic oil decreases, and the extension and retraction speed of the telescopic screed cylinder 26 slows. As described above, the extension and retraction speed of the telescopic screed cylinder 26 can be adjusted to an appropriate speed by controlling the open and closed state of the switching valve 34.

[0078] Referring back to FIG. 5, the check valve 35 of the right control valve unit 33R has a function of preventing reverse flow in the flow direction of the hydraulic oil switched by the switching valve 34. The check valve 35 is a double check valve including a first check valve 351 connected to the first line 346 and a second check valve 352 connected to the second line. The first check valve 351 allows the hydraulic oil supplied from the switching valve 34 to the base-side oil chamber 261a to pass through the first check valve 351. The second check valve 352 allows the hydraulic oil supplied from the switching valve 34 to the rod-side oil chamber 261b to pass through the second check valve 352. The first check valve 351 and the second check valve 352 allow leak of the hydraulic oil from the switching valve 34 to flow to the discharge line 271 when the supply of the hydraulic oil is stopped.

[0079] Further, the right telescopic screed cylinder 26R is provided with the screed position sensor 51C for detecting the amount of extension and retraction of the piston rod 262. For example, the screed position sensor 51C is provided inside or outside the cylinder body 261 and detects the amount of extension and retraction of the piston rod 262 that extends and retracts to the outside and transmits the detected amount to the controller 50. The controller 50 can calculate the current position of the right side frame 32R of the screed 3 based on the detected information of the screed position sensor 51C.

[0080] Then, the controller 50 (screed control part 50d) sets the target extension speed of the telescopic screed cylinder 26 based on the deviation (deviation amount) between the right side frame target path RTP and the current position of the right side frame 32R. For example, when the right side frame 32R is deviated from the right side frame target path RTP after a minute time, the target extension speed of the right telescopic screed cylinder 26R corresponding to the deviation amount is calculated.

[0081] At this time, the screed control part 50d preferably calculates the target extension speed by considering the travel speed, steering angle, and control cycle of the asphalt finisher 100. For example, when the travel speed is high, the target extension speed of the right telescopic screed cylinder 26R is corrected to be high in order to reach the target position (the position where the deviation occurs) of the right side frame target path RTP quickly. Conversely, when the travel speed is low, the target extension speed of the right telescopic screed cylinder 26R is corrected to be low in order to reach the target position (the position where the deviation occurs) of the right side frame target path RTP slowly.

[0082] Further, for example, when the steering angle of the tractor 1 deviates from the main target path and moves toward the right side frame target path RTP, a deviation occurs between the right side frame target path RTP and the right side frame 32R. The screed control part 50d calculates the extension speed (shortening speed) of the right telescopic screed cylinder 26R based on this deviation. When the steering angle of the tractor 1 deviates from the main target path and approaches the left side frame target path LTP side, a deviation occurs between the right side frame target path RTP and the right side frame 32R. The screed control part 50d calculates the extension and retraction speed (extension speed) of the right telescopic screed cylinder 26R based on this deviation.

[0083] The control cycle when the screed extension and retraction control device 54 controls the switching valve 34 is not particularly limited, but may be set in units of one second, for example. That is, the extension and retraction speed of the right telescopic screed cylinder 26R may be set by the amount of movement by which the right telescopic screed cylinder 26R extends and retracts per unit time. For example, when the extension and retraction distance in one second is 5 cm at the maximum, the extension and retraction speed of the right telescopic screed cylinder 26R is 5 cm / s.

[0084] The control cycle may be a predetermined constant value or a variable value that varies according to the condition of the asphalt finisher 100. For example, the control cycle may be shortened when the travel speed of the asphalt finisher 100 is high, while the control cycle may be lengthened when the travel speed of the asphalt finisher 100 is low. At this time, the screed control part 50d calculates the extension and retraction speed of the right telescopic screed cylinder 26R according to the control cycle.

[0085] Next, a method of setting the extension and retraction speed of the telescopic screed cylinder 26 with respect to the target position (side frame target path) will be described with reference to FIGS. 7A to 7C. FIG. 7A is a plan view illustrating an operation of extending the right side frame 32R by the right telescopic screed cylinder 26R. FIG. 7B is a drawing illustrating an operation of the switching valve 34 when controlling the extension and retraction speed of the right telescopic screed cylinder 26R. FIG. 7C is a drawing illustrating an operation of the switching valve 34 when controlling the extension and retraction speed of a right telescopic screed cylinder 26R according to a modification.

[0086] As described above, the controller 50 of the asphalt finisher 100 can calculate the deviation (deviation amount) based on the right side frame target path RTP and the current position of the right side frame 32R. As shown in FIG. 7A, the deviation between the right side frame target path RTP and the current position of the right side frame 32R corresponds to a travel distance D when the right telescopic screed cylinder 26R extends the right side frame 32R outward in the width direction.

[0087] As shown in FIG. 7B, this travel distance D may be larger than, for example, a distance movable in one second, which is a control cycle of the right telescopic screed cylinder 26R. For example, assume that the distance advanced da in one second (i.e., displacement per unit time) is up to 5 cm (i.e., maximum extension speed is 5 cm / s), whereas the travel distance D is 13 cm. In this case, even if the right telescopic screed cylinder 26R is extended at the maximum extension speed, a time of approximately three seconds (2.6 s) is required. Additionally, if the telescopic screed cylinder 26 is moved at the maximum extension speed, the possibility that the right side frame 32R cannot be accurately positioned at the target position of the right side frame target path RTP increases due to the high speed.

[0088] Therefore, the screed control part 50d of the controller 50 executes control to decrease the extension speed of the right telescopic screed cylinder 26R at a position (timing) where the right side frame 32R approaches the target position of the right side frame target path RTP. For example, when the travel distance D is 13 cm, the extension speed is adjusted so that the right side frame 32R is exactly positioned at the target position in three seconds (three control cycles).

[0089] For example, the screed control part 50d extends the right telescopic screed cylinder 26R at the maximum extension speed (5 cm / s) in the first two seconds (two control cycles). At this time, the duty ratio of the switching valve 34 becomes 100%, and the operating oil of the maximum flow rate flows into the base-side oil chamber 261a of the right telescopic screed cylinder 26R. The right telescopic screed cylinder 26R advances 5 cm as the distance advanced da in one second.

[0090] In the subsequent one second (third control cycle), the screed control part 50d decreases the duty ratio of the switching valve 34 to 60%. Thus, the switching valve 34 supplies the hydraulic oil whose flow rate has decreased to 60% to the right telescopic screed cylinder 26R. The right telescopic screed cylinder 26R moves the right side frame 32R by decreasing the extension and retraction speed at the time of extension. Then, the right telescopic screed cylinder 26R moves 3 cm as the distance advanced db in one second. Therefore, the right side frame 32R coincides with the target position of the right side frame target path RTP at the timing of the end of the third control cycle.

[0091] As described above, the controller 50 can move the right side frame 32R to the target position with high accuracy by decreasing the extension and retraction speed of the right telescopic screed cylinder 26R at a position close to the target position of the right side frame target path RTP. Moreover, since the time required for the movement of the right side frame 32R is substantially approximately without discrepancy, the extension and retraction operation of the right telescopic screed cylinder 26R can be completed smoothly.

[0092] The method of setting the extension and retraction speed of the telescopic screed cylinder 26 is not limited to the above, and various modifications may be adopted. For example, as shown in FIG. 7C, the position (duration) at which the extension and retraction speed of the right telescopic screed cylinder 26R is reduced is not limited to the last control cycle, but may be extended over a plurality of control cycles including the last control cycle. FIG. 7C shows an example in which the extension and retraction speed of the right telescopic screed cylinder 26R is reduced in the last two seconds (the second and third control cycles). In this case, the screed control part 50d sets the duty ratio in the last two seconds to 80%. As a result, the right telescopic screed cylinder 26R advances 4 cm as the distance dc advanced in one second, and the right side frame 32R can be brought into alignment with the target position at the end timing of the last control cycle.

[0093] Alternatively, when the extension and retraction speed of the right telescopic screed cylinder 26R is reduced in a plurality of control cycles, the extension and retraction speed may be changed in each control cycle. For example, by setting the duty ratio in the second control cycle to 90% and setting the duty ratio in the third control cycle to 70%, the extension and retraction speed of the right telescopic screed cylinder 26R can be reduced step by step.

[0094] The asphalt finisher 100 according to the embodiment is basically constructed as described above, and its operation will be described below. FIG. 8 is a flowchart illustrating a method for controlling the telescopic screed cylinder 26. In the control method of the telescopic screed cylinder 26, the controller 50 sequentially executes, for example, a processing flow of steps S101 to S107 shown in FIG. 8.

[0095] In controlling the telescopic screed cylinder 26, the side frame target path calculation part 50c of the controller 50 first calculates the left side frame target path LTP and the right side frame target path RTP (step S101). As described above, the left side frame target path LTP and the right side frame target path RTP can be calculated based on the design data and the current position of the asphalt finisher 100 (screed 3) positioned by the positioning device 51P. The left side frame target path LTP and the right side frame target path RTP may be calculated based on the detection information of the front monitoring device 51F or the lateral monitoring device, or they may be calculated based on the design data, the current position of the screed 3, and the detection information of the front monitoring device 51F and the lateral monitoring device.

[0096] Next, the screed control part 50d acquires the current position of the left side frame 32L and the current position of the right side frame 32R based on the detection information of the screed position sensor 51C (step S102). At this time, the screed control part 50d acquires the detection information from the screed position sensor 51C of the left telescopic screed cylinder 26L and the screed position sensor 51C of the right telescopic screed cylinder 26R.

[0097] Then, the screed control part 50d calculates a shift amount (deviation) of the left side frame 32L with respect to the left side frame target path LTP and a shift amount (deviation) of the right side frame 32R with respect to the right side frame target path RTP (step S103). As a result, the controller 50 can obtain the travel distance D of the left side frame 32L and the travel distance D of the right side frame 32R.

[0098] Subsequently, the screed control part 50d determines whether or not the shift amount of each side frame 32 is equal to or greater than a predetermined threshold value (step S104). The threshold value may be set to a value that prevents the side frames 32 from being inadvertently moved in consideration of, for example, a detection error of the current position of the side frames 32. For example, the threshold value may be set to any value within a range of approximately 0 to 3 cm. If both of the shift amounts of each side frame 32 are less than the threshold value (step S104: NO), the processing proceeds to the step S107 without executing the steps S105 and S106. Conversely, if one or both of the shift amounts of the left side frame 32L and the right side frame 32R are equal to or greater than the threshold value (step S104: YES), the processing proceeds to the step S105.

[0099] In the step S105, the screed control part 50d calculates the extension and retraction speed of the telescopic screed cylinder 26 supporting the side frame 32 equal to or greater than the threshold value (step S105). As described above, the extension and retraction speed of the telescopic screed cylinder 26 is calculated based on the capability (limit value of extension and retraction speed) of the telescopic screed cylinder 26 and the travel distance D (displacement amount) (see FIGS. 7A to 7C). Further, the screed control part 50d controls the travel distance D. The extension and retraction speed of the telescopic screed cylinder 26 may be calculated (corrected) in consideration of the travel speed, the steering angle, the control cycle, and the like.

[0100] As a result, the screed control part 50d extends and retracts the telescopic screed cylinder 26 by the threshold value or more based on the calculated extension and retraction speed, and positions the supporting side frame 32 at the target position (step S106). When the screed 3 moves the pair of side frames 32, the left telescopic screed cylinder 26L and the right telescopic screed cylinder 26R may be moved simultaneously. In the extension and retraction of the telescopic screed cylinder 26, the extension and retraction speed of the telescopic screed cylinder 26 is reduced at a position (timing) approaching the target position as described above. As a result, the side frame 32 to be extended and retracted can be accurately moved to the target position.

[0101] Then, the controller 50 determines whether or not construction of the asphalt finisher 100 ends (step S107). There are various patterns for determining the completion of construction, such as recognizing that the automatic control is turned off by the operator, recognizing that the movement of the tractor 1 has stopped, recognizing that the final target position of the target path has been reached, and the like. When the construction is continued (step S107: NO), the controller 50 returns to the step S101 and repeats the following similar processing. If the left side frame target path LTP and the right side frame target path RTP are not recalculated (corrected), the processing returns to the step S102 and the same processing may be repeated.

[0102] Conversely, when the construction ends (step S107: YES), the controller 50 ends the control method of the telescopic screed cylinder 26. At the end, the controller 50 may automatically return the telescopic screed cylinder 26 to the initial position.

[0103] As described above, according to the control method of the telescopic screed cylinder 26, the side frame 32 of the screed 3 can be accurately moved to the target position by reducing the extension and retraction speed of the telescopic screed cylinder 26 at a position or timing approaching the target position. In particular, the extension and retraction speed of the telescopic screed cylinder 26 can be easily controlled by adjusting the flow rate of the hydraulic oil supplied to the telescopic screed cylinder 26 by switching the switching valve 34 on and off.

[0104] The asphalt finisher 100 according to the present disclosure is not limited to the above-described embodiment, and various modifications may be adopted. For example, it is obvious that the asphalt finisher 100 may set the duty ratio of the extension and retraction speed of the telescopic screed cylinder 26 to less than 100% from the start of extension and retraction. That is, even if there are a plurality of control cycles in accordance with the travel distance D, the asphalt finisher 100 may set the duty ratio to less than 100% from the start of extension and retraction. Further, if the travel distance D is a multiple of the moving amount per unit time, the screed control part 50d may not slow down the extension and retraction speed of the telescopic screed cylinder 26. Alternatively, if the travel distance D is a multiple of the moving amount per unit time, the control cycle may be increased (e.g., from three seconds to four seconds,) and the extension and retraction speed may be slowed down in a plurality of control cycles including the last control cycle.<NOTE>

[0105] The technical concepts and effects of the present disclosure explained in the above embodiment will be described below.

[0106] A first aspect of the present disclosure is an asphalt finisher 100 including a screed 3 configured to level paving material PV while moving in a laying direction of the paving material PV, including a telescopic screed cylinder 26 configured to move a side frame 32, which defines a leveling limit of the screed 3, by extending and retracting upon supply of hydraulic oil, a switching valve 34 capable of being switched between an open state where the hydraulic oil is supplied to the telescopic screed cylinder 26, and a closed state where supply of the hydraulic oil is stopped, a sensor (screed position sensor 51C) configured to detect information concerning a current position of the side frame 32, and a controller 50 configured to control a drive of the switching valve 34, wherein the controller 50 is configured to calculate a side frame target path, which specifies a trajectory of the side frame 32 along the laying direction, calculate an extension and retraction speed of the telescopic screed cylinder 26 based on a deviation between the side frame target path and the current position of the side frame 32 detected by the sensor, and control the telescopic screed cylinder 26 by switching the switching valve 34 between the open state and the closed state based on the extension and retraction speed.

[0107] According to the above, the asphalt finisher 100 can extend and retract the telescopic screed cylinder 26 at an appropriate extension and retraction speed under the control of the controller 50. Thus, the asphalt finisher 100 can accurately adjust the width of the screed 3 so that the side frame 32 aligns with the side frame target path. In particular, by using the side frame target path, the controller 50 can calculate the moving distance and extension and retraction speed of the telescopic screed cylinder 26 with a sufficient distance with respect to the side frame 32 reaching the target position, and can smoothly operate the telescopic screed cylinder 26. As a result, the positioning accuracy of the side frame 32 can be enhanced.

[0108] Further, the controller 50 is configured such that the extension and retraction speed of the telescopic screed cylinder 26 at a position close to the side frame target path is lower than the extension and retraction speed of the telescopic screed cylinder 26 when the side frame 32 starts moving. Thus, the asphalt finisher 100 can decrease the extension and retraction speed of the telescopic screed cylinder 26 at a position in proximity to the side frame target path to cause the side frame 32 to move along the side frame target path more accurately.

[0109] Further, the controller 50 is configured to decrease the extension and retraction speed of the telescopic screed cylinder 26 as the side frame 32 is closer to the side frame target path. Thus, the telescopic screed cylinder 26 can easily follow the target path of the side frame by reducing the speed of the side frame 32.

[0110] Further, the extension and retraction speed of the telescopic screed cylinder 26 is adjusted based on a duty ratio between the open state and the closed state of the switching valve 34, and becomes constant when the duty ratio is 100%. Thus, the controller 50 can adjust the extension and retraction speed of the telescopic screed cylinder 26 by PWM control.

[0111] Further, the controller 50 is configured to control the extension and retraction speed of the telescopic screed cylinder 26 by a preset displacement per unit time, and control the extension and retraction speed of the telescopic screed cylinder 26 throughout a plurality of unit times when a displacement until the side frame 32 reaches the side frame target path exceeds the displacement per unit time. Thus, even when the moving amount until the side frame 32 reaches the target path of the side frame is large, the extension and retraction speed of the telescopic screed cylinder 26 can be appropriately adjusted.

[0112] Further, when the telescopic screed cylinder 26 extends or retracts throughout the plurality of unit times, the controller 50 is configured such that the displacement per unit time when the side frame 32 completes movement is smaller than the displacement per unit time when the side frame 32 begins movement. Thus, even when the telescopic screed cylinder 26 is extended or retracted for a plurality of unit times (control cycle), the side frame 32 can be accurately positioned while reducing delay in time.

[0113] The controller 50 is configured to calculate the side frame target path based on at least one of construction data and information on a current position of the asphalt finisher 100, and detection information on an external environment of the asphalt finisher 100. Thus, the controller 50 can easily calculate the target path of the side frame along the side frame 32 of the screed 3.

[0114] Further, the asphalt finisher 100 is not limited to the disclosed embodiment, and various variations and modifications may be made without departing from the scope of the present invention.

Claims

1. An asphalt finisher including a screed configured to level paving material while moving in a laying direction of the paving material, comprising:a telescopic screed cylinder configured to move a side frame, which defines a leveling limit of the screed, by extending and retracting upon supply of hydraulic oil;a switching valve capable of being switched between an open state where the hydraulic oil is supplied to the telescopic screed cylinder, and a closed state where supply of the hydraulic oil is stopped;a sensor configured to detect information concerning a current position of the side frame; anda controller configured to control a drive of the switching valve,wherein the controller is configured to:calculate a side frame target path, which specifies a trajectory of the side frame along the laying direction;calculate an extension and retraction speed of the telescopic screed cylinder based on a deviation between the side frame target path and the current position of the side frame detected by the sensor; andcontrol the telescopic screed cylinder by switching the switching valve between the open state and the closed state based on the extension and retraction speed.

2. The asphalt finisher according to claim 1, wherein the controller is configured such that the extension and retraction speed of the telescopic screed cylinder at a position close to the side frame target path is lower than the extension and retraction speed of the telescopic screed cylinder when the side frame starts moving.

3. The asphalt finisher according to claim 2, wherein the controller is configured to decrease the extension and retraction speed of the telescopic screed cylinder as the side frame is closer to the side frame target path.

4. The asphalt finisher according to claim 1, wherein the extension and retraction speed of the telescopic screed cylinder is adjusted based on a duty ratio between the open state and the closed state of the switching valve, and becomes constant when the duty ratio is 100%.

5. The asphalt finisher according to claim 1, wherein the controller is configured to:control the extension and retraction speed of the telescopic screed cylinder by a preset displacement per unit time; andcontrol the extension and retraction speed of the telescopic screed cylinder throughout a plurality of unit times when a displacement until the side frame reaches the side frame target path exceeds the displacement per unit time.

6. The asphalt finisher according to claim 5, wherein when the telescopic screed cylinder extends or retracts throughout the plurality of unit times, the controller is configured such that the displacement per unit time when the side frame completes movement is smaller than the displacement per unit time when the side frame begins movement.

7. The asphalt finisher according to claim 1, wherein the controller is configured to calculate the side frame target path based on at least one of construction data or information on a current position of the asphalt finisher, and detection information on an external environment of the asphalt finisher.

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