ASPHALT FINISHER

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application is based upon and claims priority to Japanese Patent Application No. 2024-211156, filed on December 4, 2024, the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

[0002]The present disclosure relates to an asphalt finisher.

2. Description of Related Art

[0003]In recent years, asphalt finishers configured to automatically control the width of a screed in accordance with a road surface on which a paving material is to be laid and leveled have been developed. When such automatic control is performed at an extension or contraction (extension/contraction) speed at which an operator manually controls a screed extendible or contractible (extendible/contractible) cylinder configured to change the width of a screed, the extension/contraction speed of the screed extendible/contractible cylinder can be too high. In this case, there is a possibility that accuracy in adjusting the width of the screed to a target position will be low. Conversely, when the extension/contraction speed of the screed extendible/contractible cylinder of an asphalt finisher is decreased for increasing accuracy of control, movements of the asphalt finisher become slow when the asphalt finisher is manually operated.

[0004]In view of this, the extension/contraction speed of the screed is considered to be variable. For example, related art discloses an asphalt finisher configured such that a detection sensor provided to the screed detects a construction boundary with a surface to be paved, and when the outer end of a widener is deviated from the construction boundary, the deviation of the outer end of the widener is returned while adjusting the extension/contraction speed of the widener.

SUMMARY

[0005]According to an aspect of the present disclosure, an asphalt finisher includes: a screed configured to move in a construction direction and level a paving material; a screed extendible or contractible cylinder configured to extend or contract in accordance with supply of hydraulic oil, thereby moving a side frame that is a limit of leveling by the screed; a hydraulic pump configured to supply the hydraulic oil to the screed extendible or contractible cylinder; a switching valve configured to switch a supply target of the hydraulic oil; and a proportional valve configured to adjust a flow rate of the hydraulic oil. The switching valve and the proportional valve are provided in a path between the hydraulic pump and the screed extendible or contractible cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 is a side diagram of an asphalt finisher according to an embodiment of the present disclosure;

[0007]FIG. 2 is a plan diagram of the asphalt finisher;

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

[0009]FIG. 4 is a plan diagram of a construction site where the asphalt finisher passes through a road to be constructed;

[0010]FIG. 5 is a diagram illustrating a hydraulic circuit for a left screed extendible/contractible cylinder; and

[0011]FIG. 6 is a flowchart illustrating a control method of a screed extendible/contractible cylinder.

DETAILED DESCRIPTION

[0012]The technique described in the related art performs control to return the deviation of the outer end of the widener by gradually increasing the extension/contraction speed of a hydraulic cylinder using PWM control to turn on or off a hydraulic switching valve for extension/contraction. When the extension/contraction speed is high, the width of the screed cannot be positioned with high accuracy.

[0013]Also, as a configuration for varying the extension/contraction speed of the cylinder, a proportional valve configured to adjust the flow rate of hydraulic oil is used instead of the switching valve. However, when the proportional valve is simply used, fluctuation in the flow rate of hydraulic oil becomes greater upon switching between extension and contraction. As a result, it takes time until the flow rate is stabilized.

[0014]The present disclosure provides an asphalt finisher configured to stabilize the flow rate of hydraulic oil and extend or contract (extend/contract) the width of a screed at an appropriate speed.

[0015]Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same components are denoted by the same symbols, and duplicate description thereof may be omitted.

[0016]FIG. 1 is a side diagram of an asphalt finisher 100 according to an embodiment of the present disclosure. FIG. 2 is a plan diagram of the asphalt finisher 100. The asphalt finisher 100 according to the embodiment is a wheel-type asphalt finisher, and mainly includes a tractor 1, a hopper 2, and screeds 3. In the following, a direction of the hopper 2 as viewed from the tractor 1 (+X direction) is regarded to be forward, and a direction of the screeds 3 as viewed from the tractor 1 (-X direction) is regarded to be rearward.

[0017]The tractor 1 is a mechanism configured to move the asphalt finisher 100. Specifically, the tractor 1 moves the asphalt finisher 100 by rotating rear wheels 5 using rear wheel drive hydraulic motors and rotating front wheels 6 using front wheel drive hydraulic motors. The rear wheel drive hydraulic motors and the front wheel drive hydraulic motors are configured to rotate by receiving hydraulic oil suppled from a hydraulic pump. The rear wheels 5 or the front wheels 6 may be driven wheels. Also, 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.

[0018]The asphalt finisher 100 includes a controller 50 that is a control part configured to control various components. The controller 50 is, for example, a microcomputer including a processor, a memory (e.g., a volatile storage device or a non-volatile storage device), and an input/output interface, and is mounted in the tractor 1. Each function of the controller 50 is implemented by the processor executing a program stored in the non-volatile storage device. However, each function of the controller 50 may be implemented not only by software, but also by hardware or a combination of hardware and software.

[0019]The hopper 2 is a mechanism configured to receive a paving material. In the illustrated examples, the hopper 2 is disposed on the front side of the tractor 1, and is configured by hopper cylinders to be opened or closed in a vehicle-width direction (Y-axis direction). The asphalt finisher 100 typically receives the paving material (e.g., an asphalt mixture) from the loading bed of a dump truck with the hopper 2 fully opened. The dump truck is an example of a delivery vehicle configured to deliver a paving material. FIGS. 1 and 2 illustrate a state in which the hopper 2 is fully opened. When the amount of the paving material in the hopper 2 decreases, the hopper 2 is closed and the paving material near the inner walls of the hopper 2 is collected toward a center portion of the hopper 2. By this, conveyors CV at the center portion of the hopper 2 can convey the paving material to the rear side of the tractor 1. The paving material conveyed to the rear side of the tractor 1 is laid and spread in the vehicle-width direction by a screw SC on the rear side of the tractor 1 and on the front side of the screeds 3. In the illustrated examples, the screw SC is extension screws connected on the left and right. For ease of understanding, FIGS. 1 and 2 omit illustration of a paving material in the hopper 2. In addition, a paving material PV laid and spread by the screw SC is shown by a rough dot pattern, and a new pavement body NP leveled by the screed 3 is shown by a fine dot pattern.

[0020]The screeds 3 are a mechanism configured to level the paving material PV. The screeds 3 according to the embodiment include front screeds 30 and rear screeds 31. The front screeds 30 include a left front screed 30L and a right front screed 30R. The rear screeds 31 are extendible/contractible in the vehicle-width direction, and include a left rear screed 31L and a right rear screed 31R. The rear screeds 31 are extended/contracted by screed extendible/contractible cylinders 26 in the vehicle-width direction. Specifically, the left rear screed 31L is extended/contracted by a left screed extendible/contractible cylinder 26L in the vehicle-width direction. The right rear screed 31R is extended/contracted by a right screed extendible/contractible cylinder 26R in the vehicle-width direction. Also, the screeds 3 are each a floating screed pulled by the tractor 1, and are connected to the tractor 1 via leveling arms 3A. The leveling arms 3A include a left leveling arm 3AL disposed on the left side of the tractor 1, and a right leveling arm 3AR disposed on the right side of the tractor 1.

[0021]Mold boards 43 are attached to the front portions of the screeds 3. The mold boards 43 are configured to adjust the amount of the paving material PV remaining in front of the screeds 3. The paving material PV reaches the underside of the screeds 3 through a gap between the lower ends of the mold boards 43 and a subbase BS.

[0022]A pair of side frames 32 (a left side frame 32L and a right side frame 32R) defining a limit of leveling of the paving material PV are respectively attached to both widthwise ends of the rear screed 31. The left side frame 32L extends over a predetermined length in the front-rear direction at the left end of the left rear screed 31L. The left side frame 32L is displaced in the vehicle-width direction through extension/contraction of the left screed extendible/contractible cylinder 26L. The right side frame 32R extends over a predetermined length in the front-rear direction at the right end of the right rear screed 31R. The right side frame 32R is displaced in the vehicle-width direction through extension/contraction of the right screed extendible/contractible cylinder 26R.

[0023]Also, the tractor 1 includes an information obtainment device 51, an in-vehicle display device 52, a steering device 53, and a screed extension/contraction control device 54.

[0024]The information obtainment device 51 is configured to obtain information of a road to be constructed, and output the obtained information to the controller 50. The information of the road to be constructed includes, for example, the width of the road, a change in curvature in a section with an easement curve (a section with a clothoid curve), and the curvature in an arc section. The information obtainment device 51 includes, for example, a forward monitoring device 51F, a rearward monitoring device 51B, a moving speed sensor 51S, a positioning device 51P, and a communication device 51T.

[0025]The forward monitoring device 51F obtains information of a space in front of the asphalt finisher 100. The forward monitoring device 51F can be a camera or LiDAR sensor configured to monitor a monitoring range RF in front of the tractor 1. The forward monitoring device 51F is attached to a center portion of the tractor 1 (e.g., the front-end center of a cover covering an engine room on the rear side of the hopper 2). Alternatively, the forward monitoring device 51F may be attached to any other portion of the asphalt finisher 100. The forward monitoring device 51F may be configured as a combination of a plurality of cameras and a plurality of LiDAR sensors. For example, the LiDAR sensors may include a right front LiDAR sensor attached to the front-end right portion of the tractor 1 and a left front LiDAR sensor attached to the front-end left portion of the tractor 1.

[0026]The rearward monitoring device 51B is configured to obtain information of a space rearward of the asphalt finisher 100. The rearward monitoring device 51B can be a camera or LiDAR sensor configured to monitor a monitoring range RB rearward of the screeds 3. The rearward monitoring device 51B is attached to a guide rail 1G configured to function as a handrail. Alternatively, the rearward monitoring device 51B may be attached to a lower portion of a driver’s seat 1S, or may be attached to any other portion of the asphalt finisher 100. The rearward monitoring device 51B may be configured as a combination of a plurality of cameras and a plurality of LiDAR sensors. For example, the LiDAR sensors may include a right rear LiDAR sensor attached to the rear-end right portion of the tractor 1 and a left rear LiDAR sensor attached to the rear-end left portion of the tractor 1.

[0027]The information obtainment device 51 may include lateral monitoring devices each configured to monitor a space lateral to 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 sensor configured to monitor a monitoring range on the left side 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 sensor configured to monitor a monitoring range on the right side of the tractor 1, and is attached to the right end of the upper surface of the tractor 1.

[0028]The camera may be a monocular camera or a stereo camera, and is configured to photograph surrounding images to obtain photograph information. The LiDAR sensor is, for example, configured to measure distances between many points within the monitoring range and the LiDAR sensor. However, either or both of the forward monitoring device 51F and the rearward monitoring device 51B do not necessarily need to be a camera or LiDAR sensor, and may be a millimeter wave radar sensor, a laser radar sensor, a laser scanner, a distance image camera, a laser range finder, or the like. The same applies to the lateral monitoring devices.

[0029]The forward monitoring device 51F is desirably configured to detect the monitoring range RF including the subbase BS and a feature AP located outside the subbase BS. This is for obtaining information of the width of the road to be constructed. The same applies to the monitoring ranges of the lateral monitoring devices. In the illustrated examples, the monitoring range RF has a width greater than the width of the subbase BS. The feature AP is, for example, a mold frame for pavement, an L-shaped gutter block, a curb block, or an existing pavement body.

[0030]The rearward monitoring device 51B is desirably configured to detect the monitoring range RB including the new pavement body NP and the feature AP located outside the new pavement body NP. This is for obtaining information of the width of the new pavement body NP. In the illustrated examples, the monitoring range RB has a width greater than the width of the new pavement body NP.

[0031]The moving speed sensor 51S is configured to detect the moving speed of the asphalt finisher 100. For example, the moving speed sensor 51S is a wheel speed sensor, and is configured to detect the rotational angular speed and rotational angle of the rear wheels 5, and hence detect the moving speed and moving distance of the asphalt finisher 100.

[0032]The positioning device 51P is configured to measure the position of the asphalt finisher 100. For example, the positioning device 51P is a GNSS compass, and is configured to measure the position and posture of the asphalt finisher 100. The GNSS compass serving 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 a pole PR at the rear end of the right leveling arm 3AR.

[0033]Alternatively, the positioning device 51P may be a total station. In this case, a reflecting prism to serve as a target of the total station is attached to a tip end of the pole PL. The body of the total station disposed around the asphalt finisher 100 is connected to the controller 50 via wireless communication. That is, the body of the total station transmits, to the controller 50, information of the position of the target that was derived.

[0034]The communication device 51T is configured to perform information communication between the asphalt finisher 100 and devices outside the asphalt finisher 100. In the illustrated examples, the communication device 51T is disposed in front of the driver’s seat 1S, and is configured to enable communication via a mobile communication network, a short-range wireless communication network, a satellite communication network, or the like.

[0035]Also, the information obtainment device 51 may include a steering angle sensor 51R configured to detect the steering angle of the asphalt finisher 100 (see FIG. 3), a screed position sensor 51C configured to calculate the positions of the side frames 32 (see FIG. 3), and the like.

[0036]Further, the information obtainment device 51 may include a monitoring device disposed at the construction site, or a monitoring device attached to a flying object flying over the asphalt finisher 100. The monitoring device disposed at the construction site is, for example, a camera or LiDAR sensor attached to the tip end of a pole disposed along the road to be constructed. The monitoring device attached to the flying object is, for example, a camera or LiDAR sensor attached to a multicopter (drone), an airship, or the like.

[0037]The in-vehicle display device 52 is configured to display information of the asphalt finisher 100. The in-vehicle display device 52 according to the embodiment is a liquid crystal display disposed in front of the driver’s seat 1S. The in-vehicle display device 52 may be disposed, for example, at the left or right end of the screed 3.

[0038]The steering device 53 is a device configured to perform steering of the asphalt finisher 100. The steering device 53 according to the embodiment extends or contracts a front wheel steering cylinder disposed near a front axle. Specifically, the steering device 53 includes a steering electromagnetic control valve configured to control: the flow rate of hydraulic oil flowing from a hydraulic pump to the front wheel steering cylinder; and the flow rate of hydraulic oil discharged from the front wheel steering cylinder. The steering electromagnetic control valve controls inflow or outflow (inflow/outflow) of hydraulic oil in the front wheel steering cylinder in accordance with rotation of a steering wheel SH serving as an operating device. Alternatively, the steering electromagnetic control valve is configured to control inflow/outflow of 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 operation of the steering wheel SH performed by an operator.

[0039]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 configured to control the flow rate of hydraulic oil flowing from a hydraulic pump to a left moving hydraulic motor configured to rotate the left crawler, and a right electromagnetic control valve configured to control the flow rate of hydraulic oil flowing from a hydraulic pump to a right moving hydraulic motor configured to rotate the right crawler. The left electromagnetic control valve controls inflow/outflow of hydraulic oil in the left moving hydraulic motor in accordance with an amount of operation (tilt angle) of a left operation lever, which is an operating device configured to operate the left crawler. Alternatively, the left electromagnetic control valve is configured to control inflow/outflow of hydraulic oil in the left moving hydraulic motor in accordance with a control command from the controller 50 independently of operation of the left operation lever performed by an operator. Similarly, the right electromagnetic control valve controls inflow/outflow of hydraulic oil in the right moving hydraulic motor in accordance with an amount of operation (tilt angle) of a right operation lever, which is an operating device configured to operate the right crawler. Alternatively, the right electromagnetic control valve is configured to control inflow/outflow of hydraulic oil in the right moving hydraulic motor in accordance with a control command from the controller 50 independently of operation of the right operation lever performed by an operator.

[0040]The screed extension/contraction control device 54 is configured to control the screed extendible/contractible cylinder 26 to extend/contract the rear screeds 31. Specifically, each of the screeds 3 includes a switching valve 33 configured to control the flowing direction of hydraulic oil from the hydraulic pump to the screed extendible/contractible cylinder 26, and a control valve unit 35 configured to control the flow rate of hydraulic oil (see FIG. 5). The screed extension/contraction control device 54 controls driving of the switching valve 33 and the control valve unit 35.

[0041]The screed extension/contraction control device 54 controls inflow/outflow of hydraulic oil in the screed extendible/contractible cylinder 26 in accordance with on/off operation of a screed extension/contraction switch (not shown), which is an operating device. The screed extension/contraction control device 54 is configured to control inflow/outflow of hydraulic oil in the screed extendible/contractible cylinder 26 in accordance with a control command from the controller 50 independently of operation of the screed extension/contraction switch. That is, the controller 50 can automatically control an amount of extension/contraction of the rear screeds 31 independently of operation of the screed extension/contraction switch performed by an operator. The control of the screed extendible/contractible cylinder 26 will be described below in detail.

[0042]The switching valve 33 includes a left switching valve 33L and a right switching valve 33R. Under control performed by the screed extension/contraction control device 54, the left switching valve 33L and the right switching valve 33R control extension/contraction of the left rear screed 31L and extension/contraction of the right rear screed 31R. The control valve unit 35 includes a left control valve unit 35L and a right control valve unit 35R. Under control performed by the screed extension/contraction control device 54, the left control valve unit 35L and the right control valve unit 35R control the flow rate of hydraulic oil in the left rear screed 31L and the flow rate of hydraulic oil in the right rear screed 31R. Specifically, the left switching valve 33L and the left control valve unit 35L control inflow/outflow of hydraulic oil flowing from a hydraulic pump to the left screed extendible/contractible cylinder 26L in accordance with operation of a left screed extension/contraction switch (not shown), which is an operating device. Also, the left switching valve 33L and the left control valve unit 35L control inflow/outflow of hydraulic oil flowing from a hydraulic pump to the left screed extendible/contractible cylinder 26L in accordance with a control command from the controller 50 independently of operation of the left screed extension/contraction switch. The same applies to the right electromagnetic control valve.

[0043]Next, a configuration example of an automatic steering system DS mounted in the asphalt finisher 100 will be described with reference to FIG. 3. FIG. 3 is a block diagram illustrating a configuration example of the automatic steering system DS.

[0044]The automatic steering system DS mainly includes the controller 50, the forward monitoring device 51F, the rearward monitoring device 51B, the moving speed sensor 51S, the positioning device 51P, the steering angle sensor 51R, the screed position sensor 51C, the communication device 51T, the in-vehicle display device 52, the steering device 53, the screed extension/contraction control device 54, and the like.

[0045]In the example illustrated in FIG. 3, the controller 50 includes, as functional blocks, a target calculation part 50a, a steering control part 50b, a side frame target trajectory calculation part 50c, and a screed control part 50d.

[0046]The target calculation part 50a calculates a target to be used by the steering control part 50b. The target used by the steering control part 50b is, for example, a main target trajectory to be followed by a predetermined point of the asphalt finisher 100. Strictly speaking, the target trajectory is a two-dimensional array of a large number of target positions. Alternatively, the target to be used by the steering control part 50b may be a target position serving as a location to be reached by the predetermined point of the asphalt finisher 100 after a predetermined time passes. The predetermined time may be, for example, several milliseconds, several tens of milliseconds, several hundreds of milliseconds, or several seconds.

[0047]The predetermined point of the asphalt finisher 100 is positioned on a front-rear axis of the tractor 1, and is desirably set to be positioned forward of the screed 3. The predetermined point may be, for example, set to be the center, the front-end center, or the rear-end center of the tractor 1, the hopper 2, or the screed 3. The predetermined point of the asphalt finisher 100 according to the embodiment is set to be the widthwise center of the screed 3 (front screed 30).

[0048]The target calculation part 50a calculates a main target trajectory to be followed by the predetermined point of the screed 3 in the construction direction of the asphalt finisher 100 based on information of the road to be constructed, such as construction data (design data) or the like. Typically, the main target trajectory is calculated before the asphalt finisher 100 starts to move. Therefore, the main target trajectory may be calculated by a server or the like disposed in a management center located outside the asphalt finisher 100, and then transmitted to the controller 50 via communication.

[0049]The target calculation part 50a may calculate the main target position as a location to be reached by the predetermined point of the screed 3 after a predetermined time passes. In this case, the main target position is repeatedly calculated in a predetermined control cycle while the asphalt finisher 100 is moving. For example, when the asphalt finisher 100 moves on a straight portion of the road to be constructed, the target calculation part 50a may calculate, as the main target position, a center point in the width direction of the road to be constructed, which is located a predetermined distance in front of the current position of the predetermined point of the screed 3, based on information obtained by the forward monitoring device 51F. The predetermined distance is, for example, several centimeters to several tens of centimeters. This enables the target calculation part 50a to calculate the main target position without obtaining design data. However, the target calculation part 50a may calculate the main target position based on the design data and the information obtained by the forward monitoring device 51F. For example, the target calculation part 50a may correct the main target position calculated based on the design data based on the information obtained by the forward monitoring device 51F. Alternatively, the target calculation part 50a may correct the main target position using the information obtained by the rearward monitoring device 51B.

[0050]The steering control part 50b automatically controls the steering of the asphalt finisher 100 as an assistance for an operation performed by an operator.

[0051]The steering control part 50b according to the embodiment outputs a control command to the steering device 53 such that the set predetermined point of the screed 3 follows the main target trajectory 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. For example, if the steering control part 50b determines that the predetermined point deviates rightward from the main target trajectory, the steering control part 50b outputs a control command to the steering device 53 such that the tractor 1 moves leftward. Similarly, when the steering control part 50b determines that the predetermined point deviates leftward from the main target trajectory, the steering control part 50b outputs a control command to the steering device 53 such that the asphalt finisher 100 moves rightward.

[0052]Alternatively, the steering control part 50b may output a control command to the steering device 53 such that the predetermined point of the screed 3 is along 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 rearward monitoring device 51B or the forward monitoring device 51F.

[0053]Next, a function of moving the asphalt finisher 100 along the target trajectory will be described with reference to FIG. 4. FIG. 4 is a plan diagram of a construction site where the asphalt finisher 100 passes through a straight portion SP1, a curved portion LC (left curve), and a 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 the time of start of construction, is indicated by a reference symbol 100a. The asphalt finisher 100 at a second point in time, which is after a predetermined time passed from the first point in time, is indicated by a reference symbol 100b. Similarly, the asphalt finisher 100 at a third point in time, which is after a predetermined time passed from the second point in time, is indicated by a reference symbol 100c. The asphalt finisher 100 at a fourth point in time, which is after a predetermined time passed from the third point in time, is indicated by a reference symbol 100d. The asphalt finisher 100 at a fifth point in time, which is after a predetermined time passed from the fourth point in time, is indicated by a reference symbol 100e. For clarity, FIG. 4 simplifies illustration of the tractor 1, the front screeds 30, the left rear screed 31L, and the right rear screed 31R of the asphalt finisher 100.

[0054]The target calculation part 50a of the controller 50 calculates a main target trajectory TPS to be followed by a predetermined point Q of the screed 3 at the first point in time, which is the time of start of construction. In FIG. 4, the predetermined point Q is shown by a triangle, and the main target trajectory TPS is shown by a dashed-dotted line. For example, the target calculation part 50a refers to design data, and derives the main target trajectory TPS based on a left boundary and a right boundary of the road RD to be constructed. In FIG. 4, a center line CP of the road RD is shown by a dashed line. The main target trajectory TPS may be generated based on a line that equally divides the area of a road surface to be leveled by the screed 3 into two on the left and right sides. The area of the road surface is, for example, the area of a road surface leveled when the asphalt finisher 100 moves forward a predetermined distance.

[0055]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 causes the asphalt finisher 100 to move such that a set of actual position coordinates of the predetermined point Q coincide with one of the sets of the position coordinates forming the main target trajectory TPS. By this, the steering control part 50b moves the predetermined point Q 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.

[0056]For the movement of the asphalt finisher 100, the position of the left side frame 32L at the left end of the left rear screed 31L is controlled to be along a left side frame target trajectory LTP calculated by the controller 50. Similarly, the position of the right side frame 32R at the right end of the right rear screed 31R is controlled to be along a right side frame target trajectory RTP calculated by the controller 50.

[0057]Therefore, the side frame target trajectory calculation part 50c of the controller 50 illustrated in FIG. 3 calculates the left side frame target trajectory LTP and the right side frame target trajectory RTP even if the tractor 1 is caused to move forward such that the predetermined point Q follows the main target trajectory TPS. The left side frame target trajectory LTP is basically calculated as a line corresponding to the left boundary of the road RD. However, the left side frame target trajectory LTP can be calculated as a line different from the left boundary in accordance with capabilities of the asphalt finisher 100 (e.g., a limit of extension/contraction of the screed 3 or a speed of extension/contraction of the screed 3). Similarly, the right side frame target trajectory RTP is basically calculated as a line corresponding to the right boundary of the road RD. However, the right side frame target trajectory RTP can be calculated as a line different from the left boundary in accordance with capabilities of the asphalt finisher 100 (e.g., a limit of extension/contraction of the screed 3 or a speed of extension/contraction of the screed 3).

[0058]For example, the side frame target trajectory calculation part 50c can calculate the left side frame target trajectory LTP and the right side frame target trajectory RTP based on construction data obtained in advance and a position of the asphalt finisher 100 measured by the positioning device 51P. In this case, the side frame target trajectory calculation part 50c may calculate, before construction, the left side frame target trajectory LTP and the right side frame target trajectory RTP. Also, the side frame target trajectory calculation part 50c can calculate, during construction, the left side frame target trajectory LTP and the right side frame target trajectory RTP based on detection information detected by the forward monitoring device 51F or the lateral monitoring devices. For example, the left side frame target trajectory LTP and the right side frame target trajectory RTP are calculated based on information, detected by the forward monitoring device 51F, of a left side boundary and a right side boundary several meters ahead of the asphalt finisher 100. Alternatively, the side frame target trajectory calculation part 50c may calculate the left side frame target trajectory LTP and the right side frame target trajectory RTP using construction data, a position of the asphalt finisher 100, and detection information detected by the forward monitoring device 51F or the lateral monitoring devices.

[0059]The screed control part 50d of the controller 50 outputs a control command to the screed extension/contraction control device 54 based on the left side frame target trajectory LTP and the right side frame target trajectory RTP that are calculated by the side frame target trajectory calculation part 50c, thereby controlling the movement of the screed 3. The screed control part 50d outputs a control command such that the left side frame 32L of the left rear screed 31L coincides with the left side frame target trajectory LTP, and the right side frame 32R of the right rear screed 31R coincides with the right side frame target trajectory RTP.

[0060]For example, if there is a possibility that the left side frame 32L deviates inward of the left side frame target trajectory LTP, the left side frame 32L is extended leftward. Conversely, if there is a possibility that the left side frame 32L deviates outward of the left side frame target trajectory LTP, the left side frame 32L is contracted rightward. If there is a possibility that the right side frame 32R deviates inward of the right side frame target trajectory RTP, the right side frame 32R is extended rightward. Conversely, if the right side frame 32R deviates outward of the right side frame target trajectory RTP, the right side frame 32R is contracted leftward. By this, construction is performed such that the side frame target trajectories (the left side frame target trajectory LTP and the right side frame target trajectory RTP) coincide with the width of the new pavement body NP (width of the screed 3).

[0061]Next, a specific configuration of a hydraulic circuit including the switching valve 33 and the control valve unit 35 configured to extend/contract the screed extendible/contractible cylinder 26 will be described. FIG. 5 is a diagram illustrating a hydraulic circuit for the left screed extendible/contractible cylinder 26L. In the following, as illustrated in FIG. 5, the hydraulic circuit for extending/contracting the left screed extendible/contractible cylinder 26L will be described as an example. Description of a similarly configured hydraulic circuit for extending/contracting the right screed extendible/contractible cylinder 26R will be omitted.

[0062]The hydraulic circuit for the left screed extendible/contractible cylinder 26L includes the left switching valve 33L, a check valve 34, and the left control valve unit 35L, which are disposed between a hydraulic pump 25, connected to a storage tank 24 for hydraulic oil, and the left screed extendible/contractible cylinder 26L. The left control valve unit 35L includes a bidirectional electromagnetic proportional flow valve (hereinafter referred to simply as a proportional valve 36), a pressure compensation valve 37, and a drive switching valve 38. Also, the hydraulic circuit connects a tank 27 to the left switching valve 33L, and the tank 27 is configured to recover hydraulic oil discharged from the left screed extendible/contractible cylinder 26L.

[0063]The left screed extendible/contractible cylinder 26L connected to the hydraulic circuit includes a piston rod 262 that divides the inner space of a cylinder body 261 into a base end-side oil chamber 261a and a rod-side oil chamber 261b. The left rear screed 31L (see FIG. 2) is connected to the piston rod 262. The left screed extendible/contractible cylinder 26L extends the piston rod 262 toward the tip end as hydraulic oil is supplied from the left switching valve 33L to the base end-side oil chamber 261a. By this, the left side frame 32L of the left rear screed 31L is displaced outward in the width direction of the screed 3. Conversely, the left screed extendible/contractible cylinder 26L contracts the piston rod 262 toward the base end as hydraulic oil is supplied from the left control valve unit 35L to the rod-side oil chamber 261b. By this, the left side frame 32L of the left rear screed 31L is displaced inward in the width direction of the screed 3.

[0064]The left switching valve 33L has: a function of selectively supplying hydraulic oil to the base end-side oil chamber 261a and the rod-side oil chamber 261b of the left screed extendible/contractible cylinder 26L which is a supply target of hydraulic oil; and a function of stopping the supply of hydraulic oil. A portion of the left switching valve 33L on one end side of the left switching valve 33L is connected to the hydraulic pump 25 through a supply line 251 and to the tank 27 through a discharge line 271. A portion of the left switching valve 33L on the other end side of the left switching valve 33L is connected to a first check valve 341 of the check valve 34 through a first line 336 and to a second check valve 342 of the check valve 34 through a second line 337.

[0065]The supply line 251, the discharge line 271, the first line 336, and the second line 337 are connected to the body of the left switching valve 33L, and communicate with three switching path sections based on the position of a spool 331 moving forward and rearward in the body. The three switching path sections are: a supply stop section 333 that stops the supply of hydraulic oil to the left screed extendible/contractible cylinder 26L; a base end-side supply section 334 that supplies hydraulic oil to the base end-side oil chamber 261a of the left screed extendible/contractible cylinder 26L; and a rod-side supply section 335 that supplies hydraulic oil to the rod-side oil chamber 261b via the left control valve unit 35L.

[0066]The supply stop section 333 includes an internal path that shuts off the supply line 251 and connects the first line 336 and the second line 337 to the discharge line 271. When the spool 331 is disposed in the supply stop section 333 due to driving of an electromagnetic coil 332, the left switching valve 33L stops the supply of hydraulic oil from the hydraulic pump 25 and enables an excessive pressure of the hydraulic oil to be released through the first line 336 and the second line 337. Thus, the supply of hydraulic oil to the left screed extendible/contractible cylinder 26L is stopped, and the position of the piston rod 262 can be maintained in place.

[0067]The base end-side supply section 334 includes an internal path that connects the supply line 251 to the first line 336 in a fully open state and connects the discharge line 271 to the second line 337. When the spool 331 is disposed in the base end-side supply section 334 due to driving of the electromagnetic coil 332, the left switching valve 33L can supply hydraulic oil from the hydraulic pump 25 to the base end-side oil chamber 261a. Also, the left switching valve 33L can discharge, to the tank 27, hydraulic oil in the rod-side oil chamber 261b flowing via the left control valve unit 35L. Thus, the piston rod 262 of the left screed extendible/contractible cylinder 26L is extended.

[0068]The rod-side supply section 335 includes an internal path that connects the supply line 251 to the second line 337 in a fully open state and connects the discharge line 271 to the first line 336. When the spool 331 is disposed in the rod-side supply section 335 due to driving of the electromagnetic coil 332, the left switching valve 33L can supply hydraulic oil from the hydraulic pump 25 to the rod-side oil chamber 261b via the left control valve unit 35L. Also, the left switching valve 33L can discharge hydraulic oil from the base end-side oil chamber 261a to the tank 27. This contracts the piston rod 262 of the left screed extendible/contractible cylinder 26L. The left switching valve 33L can determine the flow direction of hydraulic oil by continuously disposing the spool 331 in the base end-side supply section 334 or the rod-side supply section 335 in accordance with supply of power from the screed extension/contraction control device 54.

[0069]The check valve 34 has a function of preventing backflow in the flow direction of hydraulic oil switched by the left switching valve 33L. The check valve 34 is a double check valve including the first check valve 341 connected to the first line 336 and the second check valve 342 connected to the second line 337. The first check valve 341 causes hydraulic oil supplied from the left switching valve 33L to flow into the base end-side oil chamber 261a. The second check valve 342 causes hydraulic oil supplied from the left switching valve 33L to flow into the rod-side oil chamber 261b via the left control valve unit 35L. Also, the first check valve 341 and the second check valve 342 cause hydraulic oil leaked from the left switching valve 33L to flow through the discharge line 271 at the stop of supply of hydraulic oil.

[0070]The first line 336 between the first check valve 341 and the base end-side oil chamber 261a is provided with a branched line 391 that is branched from the first line 336 and connected to the discharge line 271. The branched line 391 is provided with a relief valve 39.

[0071]The relief valve 39 is closed in a normal state, but is configured to open the flow path of the branched line 391 once a set pressure is reached. The relief valve 39 is opened when the pressure of hydraulic oil on the base end-side oil chamber 261a side is high. This can reduce the pressure by directly discharging a portion of the hydraulic oil in the base end-side oil chamber 261a to the tank 27.

[0072]The left control valve unit 35L linearly changes the flow rate of hydraulic oil to control the extension/contraction speed of the left screed extendible/contractible cylinder 26L. The left control valve unit 35L is an integrated structure of the proportional valve 36, the pressure compensation valve 37, and the drive switching valve 38. However, this is by no means a limitation. The pressure compensation valve 37 and the drive switching valve 38 may be disposed as separate devices.

[0073]The left control valve unit 35L is disposed in the second line 337 to control the flow rate of hydraulic oil in supply and discharge of the rod-side oil chamber 261b. In the left screed extendible/contractible cylinder 26L, the amount of supplied hydraulic oil is smaller in the rod-side oil chamber 261b, and thus the pressure loss of hydraulic oil is reduced. Alternatively, the left control valve unit 35L may be disposed in the first line 336 to control the flow rate of hydraulic oil in supply and discharge of the base end-side oil chamber 261a. Alternatively, the left control valve unit 35L may be disposed in both the first line 336 and the second line 337 to control the respective flow rates of hydraulic oil.

[0074]The proportional valve 36 of the left control valve unit 35L moves a valve disc 361 in the body by the effect of the electromagnetic coil 362. The proportional valve 36 moves the valve disc 361 between a closed mode 363, in which the flow path in the body is fully closed, and an open mode 364, in which the flow path in the body is fully opened. The valve disc 361 may be a spool or may be any other valve disc, such as a butterfly valve or the like. The valve disc 361 linearly changes the opening area of the flow path in proportion to the amount of current supplied to the electromagnetic coil 362. Thus, the proportional valve 36 can discharge hydraulic oil at a flow rate in accordance with the position of the valve disc 361.

[0075]The proportional valve 36 includes two ports for hydraulic oil, with one port being connected to a line 365 and the other port being connected to a line 366. The proportional valve 36 is a bidirectional flow valve configured to selectively perform: a pattern in which hydraulic oil flows into the one port and flows out of the other port; and a pattern in which hydraulic oil flows into the other port and flows out of the one port. Each of the lines 365 and 366 is connected to the pressure compensation valve 37.

[0076]The lines 365 and 366 are connected to a portion of the pressure compensation valve 37 on one end side of the pressure compensation valve 37. The second line 337 and a cylinder line 376, leading to the rod-side oil chamber 261b of the left screed extendible/contractible cylinder 26L, are connected to a portion of the pressure compensation valve 37 on the other end side of the pressure compensation valve 37. The pressure compensation valve 37 has a function of making constant the pressure difference between the pressure of the second line 337 and the pressure of the cylinder line 376. For example, even if the flow rate of hydraulic oil flowing through the lines changes, the pressure compensation valve 37 automatically adjusts the flow rate of hydraulic oil such that the pressure difference is made constant with the minimum compensation pressure.

[0077]The pressure compensation valve 37 includes a spool 371 disposed to be movable in the body and an electromagnetic coil 372 configured to move the spool 371 forward or rearward. The spool 371 moves in a flow path switching section provided in the body to adjust the opening area of the flow path between the second line 337 and the line 365 and to adjust the opening area of the flow path between the cylinder line 376 and the line 366. The flow path switching section has: a first open mode 373, in which the opening areas of the second line 337 and the cylinder line 376 are the same; a second open mode 374, in which the opening area on the second line 337 side is increased while the opening area on the cylinder line 376 side is decreased; and a third open mode 375, in which the opening area on the cylinder line 376 side is increased while the opening area on the second line 337 side is decreased. Here, the spool 371 can linearly move among the first open mode 373 to the third open mode 375, thereby adjusting the opening area.

[0078]For example, when hydraulic oil is supplied to the rod-side oil chamber 261b, the spool 371 moves between the first open mode 373 and the second open mode 374 to adjust the pressure difference of hydraulic oil at the time of supply to be constant. Conversely, when hydraulic oil is discharged from the rod-side oil chamber 261b, the spool 371 moves between the first open mode 373 and the third open mode 375 to adjust the pressure difference of hydraulic oil at the time of discharge to be constant.

[0079]On the other hand, the drive switching valve 38 connects a branched line of the second line 337 and a branched line of the cylinder line 376, thereby switching a communication state between the second line 337 and the cylinder line 376. The drive switching valve 38 drives a valve disc 381 provided in the body by the effect of an electromagnetic coil 382, thereby moving the valve disc 381 to an open mode 383 and a closed mode 384.

[0080]In the open mode 383, the second line 337 communicates with the cylinder line 376. Therefore, the left switching valve 33L is in communication with the rod-side oil chamber 261b. For example, when hydraulic oil is supplied from the left switching valve 33L to the rod-side oil chamber 261b, the hydraulic oil can be caused to flow without passage through the proportional valve 36 and the pressure compensation valve 37. Conversely, when hydraulic oil is discharged from the rod-side oil chamber 261b to the left switching valve 33L, the hydraulic oil can be caused to flow without passage through the proportional valve 36 and the pressure compensation valve 37.

[0081]On the other hand, in the closed mode 384, the second line 337 and the cylinder line 376 do not communicate with each other. Therefore, when hydraulic oil is supplied from the left switching valve 33L to the rod-side oil chamber 261b, the hydraulic oil can be caused to flow through the proportional valve 36 and the pressure compensation valve 37, and the flow rate of the hydraulic oil can be adjusted by the proportional valve 36 before the hydraulic oil flows into the rod-side oil chamber 261b. Conversely, when hydraulic oil is discharged from the rod-side oil chamber 261b to the left switching valve 33L, the hydraulic oil can be caused to flow through the proportional valve 36 and the pressure compensation valve 37, and the flow rate of the hydraulic oil can be adjusted by the proportional valve 36 before the hydraulic oil is discharged.

[0082]That is, the drive switching valve 38 is configured to switch between use and non-use of the proportional valve 36. With this drive switching valve 38, the left control valve unit 35L can selectively switch between a first mode in which the flow rate of hydraulic oil is adjusted by the proportional valve 36, and a second mode in which hydraulic oil is caused to flow at a constant flow rate without passage through the proportional valve 36. In other words, the left control valve unit 35L can perform the first mode in which the extension/contraction speed of the left screed extendible/contractible cylinder 26L is adjusted by the proportional valve 36, and the second mode in which the extension/contraction speed of the left screed extendible/contractible cylinder 26L is maintained by the left switching valve 33L to be constant at a limit value.

[0083]The asphalt finisher 100 according to the embodiment is basically configured as described above. Next, a control method for moving the screed extendible/contractible cylinder 26 will be described with reference to FIG. 6. FIG. 6 is a flowchart illustrating a control method of the screed extendible/contractible cylinder 26.

[0084]The screed control part 50d of the controller 50 determines whether or not to adjust the extension/contraction speed of the screed extendible/contractible cylinder 26 in the control method of the screed extendible/contractible cylinder 26 (step S101). A case in which the extension/contraction speed of the screed extendible/contractible cylinder 26 is adjusted is, for example, a case in which the width of the screed 3 is adjusted by automatic control. In the automatic control, the screed control part 50d controls the left screed extendible/contractible cylinder 26L based on the left side frame target trajectory LTP, and controls the right screed extendible/contractible cylinder 26R based on the right side frame target trajectory RTP. At this time, the screed control part 50d recognizes the current position of the left side frame 32L based on the screed position sensor 51C, and adjusts the extension/contraction speed of the left screed extendible/contractible cylinder 26L in accordance with a deviation (displacement) from the left side frame target trajectory LTP. The same applies to a case of the right screed extendible/contractible cylinder 26R. Therefore, when the screed control part 50d determines that the extension/contraction speed of the screed extendible/contractible cylinder 26 is to be adjusted in accordance with the ON state of a switch of the automatic control of the operating device (step S101: YES), the process flow proceeds to step S102.

[0085]Next, the screed control part 50d confirms a target moving direction of the screed extendible/contractible cylinder 26 (step S102). The target moving direction is a direction of extension/contraction of the screed extendible/contractible cylinder 26. For example, the left screed extendible/contractible cylinder 26L is extended when the asphalt finisher 100 moves leftward, and the left screed extendible/contractible cylinder 26L is contracted when the asphalt finisher 100 moves rightward. Conversely, the right screed extendible/contractible cylinder 26R is extended when the asphalt finisher 100 moves rightward, and the right screed extendible/contractible cylinder 26R is contracted when the asphalt finisher 100 moves leftward.

[0086]Then, the screed control part 50d calculates the extension/contraction speed of the screed extendible/contractible cylinder 26 (step S103). The extension/contraction speed of the screed extendible/contractible cylinder 26 is calculated, based on the deviation, to be lower as the current position of the side frame 32 is closer to the target position (side frame target trajectory). Thus, the asphalt finisher 100 can position the to-be-moved side frame 32 at the target position with high accuracy.

[0087]Further, the screed control part 50d calculates a power value to be input to the electromagnetic proportional flow valve (proportional valve 36) based on the calculated extension/contraction speed of the screed extendible/contractible cylinder 26 (step S104). For example, the screed control part 50d has table information or a function indicating a correspondence relationship between the extension/contraction speed of the screed extendible/contractible cylinder 26 and the power value, and refers to the table information to extract the power value corresponding to the extension/contraction speed.

[0088]The screed control part 50d transmits a control command, including the power value, to the screed extension/contraction control device 54, thereby supplying power corresponding to the power value commanded from the screed extension/contraction control device 54 to the electromagnetic proportional flow valve (proportional valve 36) (step S105). At this stage, the screed control part 50d operates the switching valve 33 in accordance with the target moving direction to select one of extension or contraction of the screed extendible/contractible cylinder 26, and operates the drive switching valve 38 to shut off the path between the second line 337 and the cylinder line 376. This causes hydraulic oil to pass through the proportional valve 36.

[0089]The opening area of the electromagnetic proportional flow valve (proportional valve 36) in the control valve unit 35 changes in accordance with the supplied power (step S106). Therefore, for example, when hydraulic oil is supplied from the hydraulic pump 25 to the rod-side oil chamber 261b, the hydraulic oil flows through the switching valve 33, the second check valve 342, the pressure compensation valve 37, and the proportional valve 36, and the flow rate of the hydraulic oil is adjusted in the proportional valve 36.

[0090]The screed extendible/contractible cylinder 26 is extended/contracted at a set extension/contraction speed by inflow of the hydraulic oil having the adjusted flow rate or by adjustment of the flow rate at the time of discharge of the hydraulic oil (step S107). Thus, the screed extendible/contractible cylinder 26 can move the supporting side frame 32 in the target moving direction.

[0091]The screed control part 50d determines whether or not the side frame 32 has reached the target position during movement of the screed extendible/contractible cylinder 26 (step S108). Whether or not the side frame 32 has reached the target position may be determined by monitoring the detection information of the screed position sensor 51C, or by monitoring the movement time of the screed extendible/contractible cylinder 26 to confirm that the target time has passed. If the side frame 32 has not reached the target position (step S108: NO), the process flow returns to step S102 and repeats a similar subsequent process. Thus, when the side frame 32 has not reached the target position, the target moving direction and the extension/contraction speed are re-calculated to output a current value again, and the output current value becomes smaller as the side frame 32 is closer to the target position. Conversely, if the side frame 32 has reached the target position (step S108: YES), the present process flow is ended.

[0092]If the automatic control of the width of the screed 3 is not performed in step S101 (step S101: NO), an operator manually controls the movement of the screed extendible/contractible cylinder 26. In this case, the process flow proceeds to step S109.

[0093]In step S109, the switching valve 33 controls the inflow/outflow of hydraulic oil to/from the screed extendible/contractible cylinder 26 in accordance with an ON/OFF operation of the screed extension/contraction switch serving as the operating device. Thus, the screed extendible/contractible cylinder 26 extends/contracts at a constant speed (limit value of the extension/contraction speed), and the width of the screed 3 can be quickly adjusted in accordance with an operating sensation of the operator.

[0094]As described above, according to the control method of the screed extendible/contractible cylinder 26, the switching valve 33 switches the target moving direction (supply target) and the proportional valve 36 adjusts the flow rate of hydraulic oil, thereby enabling adjustment of the extension/contraction speed of the screed extendible/contractible cylinder 26 to an appropriate speed. Also, when the screed extendible/contractible cylinder 26 is desired to be moved at a constant extension/contraction speed (limit value), the drive switching valve 38 is driven to cause hydraulic oil not to pass through the proportional valve 36, thereby enabling the hydraulic oil to be directly supplied from the switching valve 33 to the screed extendible/contractible cylinder 26.

[0095]Further, when the screed extendible/contractible cylinder 26 is switched from extension to contraction or from contraction to extension, the switching valve 33 moves the spool 331 between the base end-side supply section 334 and the rod-side supply section 335, thereby smoothly performing such switching. Smoothly switching the flow of hydraulic oil can stabilize the hydraulic oil at an early stage. Therefore, even if the flow rate of hydraulic oil is adjusted by the proportional valve 36, control to drive the switching valve 33 to switch the target moving direction of hydraulic oil may be performed by stopping the flow of the hydraulic oil toward the proportional valve 36 at a timing of switching between extension and contraction of the screed extendible/contractible cylinder 26.

[0096]The asphalt finisher 100 according to the present disclosure is not limited to the above-described embodiments, and may have various modified examples. For example, the hydraulic circuit of the screed extendible/contractible cylinder 26 may be configured without the pressure compensation valve 37, the drive switching valve 38, and the like. This is because supply of hydraulic oil and stoppage of supply of hydraulic oil can be appropriately switched by using any other on-off valve. Also, for example, the proportional valve 36 is not limited to the electromagnetic proportional flow valve, and the proportional valve 36 to be driven in another way may be used.

Clauses

[0097]Technical ideas and effects of the present disclosure described in the above embodiments will be described below.

[0098]According to a first aspect of the present disclosure, the asphalt finisher 100 includes: the screed 3 configured to move in the construction direction and level the paving material PV; the screed extendible/contractible cylinder 26 configured to extend/contract in accordance with supply of hydraulic oil, thereby moving the side frame 32 that is a limit of leveling by the screed 3; the hydraulic pump 25 configured to supply the hydraulic oil to the screed extendible/contractible cylinder 26; the switching valve 33 configured to switch the supply target of the hydraulic oil; and the proportional valve 36 configured to adjust the flow rate of the hydraulic oil. The switching valve 33 and the proportional valve 36 are provided in a path between the hydraulic pump 25 and the screed extendible/contractible cylinder 26.

[0099]As described above, when the asphalt finisher 100 includes the switching valve 33 and the proportional valve 36 between the hydraulic pump 25 and the screed extendible/contractible cylinder 26, it is possible to control the flow of hydraulic oil by virtue of the functions of both the switching valve 33 and the proportional valve 36. For example, according to the asphalt finisher 100, the flow rate of hydraulic oil can be stabilized by performing switching of the hydraulic oil using the switching valve 33 when the screed extendible/contractible cylinder 26 is switched between extension and contraction. Also, according to the asphalt finisher 100, the width of the screed can be extended/contracted at an appropriate speed by adjusting the flow rate of hydraulic oil using the proportional valve 36 when the extension/contraction speed of the screed extendible/contractible cylinder 26 is adjusted.

[0100]The proportional valve 36 can adjust the flow rate of hydraulic oil supplied to the screed extendible/contractible cylinder 26, and adjust the flow rate of hydraulic oil discharged from the screed extendible/contractible cylinder 26. Thus, according to the asphalt finisher 100, it is possible to readily adjust, using the single proportional valve 36, the extension/contraction speed of the screed extendible/contractible cylinder 26 at the times of both extension and contraction of the screed extendible/contractible cylinder 26.

[0101]Also, the proportional valve 36 is configured to lower the flow rate of the hydraulic oil as the side frame 32 is closer to the target position, thereby lowering the extension/contraction speed of the screed extendible/contractible cylinder 26. Thus, according to the asphalt finisher 100, it is possible to lower the extension/contraction speed of the screed extendible/contractible cylinder 26 at a position close to the target position, and to move the side frame 32 to the target position with high accuracy.

[0102]Also, the switching valve 33 is configured to cause the hydraulic oil supplied to the screed extendible/contractible cylinder 26 to flow at the upper limit of the flow rate, or to cause the hydraulic oil discharged from the screed extendible/contractible cylinder 26 to flow at the upper limit of the flow rate. With this configuration, the switching valve 33 enables the hydraulic oil to flow at a sufficient flow rate. This can, for example, efficiently perform switching between extension and contraction of the screed extendible/contractible cylinder 26.

[0103]Also, the asphalt finisher 100 further includes the drive switching valve 38 configured to switch between the first mode in which the hydraulic oil is caused to flow from the switching valve 33 or the screed extendible/contractible cylinder 26 through the proportional valve 36 and the second mode in which the hydraulic oil is caused to flow between the switching valve 33 and the screed extendible/contractible cylinder 26 without passage through the proportional valve 36. Thus, according to the asphalt finisher 100, the drive switching valve 38 can readily switch between the first mode and the second mode.

[0104]Also, the asphalt finisher 100 further includes the controller 50 configured to control the switching valve 33, the proportional valve 36, and the drive switching valve 38. The controller 50 determines whether or not to adjust the extension/contraction speed of the screed extendible/contractible cylinder 26. The controller 50 causes the drive switching valve 38 to select the first mode in a case in which the extension/contraction speed of the screed extendible/contractible cylinder 26 is adjusted. The controller 50 causes the drive switching valve 38 to select the second mode in a case in which the extension/contraction speed of the screed extendible/contractible cylinder 26 is not adjusted. Thus, according to the asphalt finisher 100, it is possible to appropriately control the extension/contraction speed of the screed extendible/contractible cylinder 26.

[0105]Also, the asphalt finisher 100 further includes the pressure compensation valve 37 configured to make constant the pressure difference between the pressure of the hydraulic oil flowing into the proportional valve 36 and the pressure of the hydraulic oil flowing out of the proportional valve 36. Thus, according to the asphalt finisher 100, it is possible to cause the flow of the hydraulic oil to be stable by making constant the pressure difference when the hydraulic oil is caused to pass through the proportional valve 36.

[0106]Also, the screed extendible/contractible cylinder 26 includes the base end-side oil chamber 261a and the rod-side oil chamber 261b that are each the supply target of the hydraulic oil. The proportional valve 36 is disposed in a path between the switching valve 33 and the rod-side oil chamber 261b. With this configuration, the proportional valve 36 can adjust the flow rate of the hydraulic oil in the rod-side oil chamber 261b, which requires a small amount of hydraulic oil to be supplied, thereby reducing the pressure loss of the hydraulic oil.

[0107]The asphalt finisher 100 according to the embodiments disclosed herein is illustrative in all respects and not restrictive. The embodiments can be modified and improved in various forms without departing from the scope and intent of claims recited. The matters described in the above embodiments can have other configurations as long as there is no contradiction, and can be combined as long as there is no contradiction.