Asphalt finisher

Abstract

To provide an asphalt finisher that can stabilize the flow rate of hydraulic fluid and expand and contract the width of the screed at an appropriate speed. [Solution] The asphalt finisher 100 is equipped with a screed 3 that spreads and levels the paving material PV while moving in the laying direction. The asphalt finisher 100 is equipped with a screed extension cylinder 26 that extends and retracts in accordance with the supply of hydraulic fluid to move the side frame 32, which is the leveling limit of the screed 3, and a hydraulic pump 25 that supplies hydraulic fluid to the screed extension cylinder 26. A switching valve 33 for switching the target to which the hydraulic fluid is supplied and a proportional valve 36 for adjusting the flow rate of the hydraulic fluid are provided in the path between the hydraulic pump 25 and the screed extension cylinder 26.

Description

Technical Field

[0001] The present disclosure relates to an asphalt finisher.

Background Art

[0002] In recent years, an asphalt finisher has been developed that automatically controls the width of the screed according to the road surface to which the paving material is evenly laid. When the screed expansion and contraction cylinder that moves the width of the screed performs automatic control at the expansion and contraction speed during manual control by an operator, the expansion and contraction speed may be too fast. In this case, the accuracy of aligning the width of the screed with the target position may decrease. Conversely, when the asphalt finisher slows down the expansion and contraction speed of the screed expansion and contraction cylinder in order to improve the control accuracy, the operation becomes slow when manually operated.

[0003] Therefore, it is conceivable to make the expansion and contraction speed of the screed variable. For example, in Patent Document 1, a laying boundary portion with the paved surface is detected by a detection sensor portion provided on the screed, and when the outer end portion of the widener is offset with respect to the laying boundary portion, an asphalt finisher is disclosed that returns the offset while adjusting the expansion and contraction speed of the widener.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the technique described in Patent Document 1, control is performed to return the offset of the outer end portion of the widener by gradually increasing the expansion and contraction speed of the hydraulic cylinder by PWM control that turns on and off the expansion and contraction hydraulic switching valve. When the expansion and contraction speed is high, the problem remains that the width of the screed cannot be accurately positioned.

[0006] Another possible configuration for varying the cylinder's extension and retraction speed is to use a proportional valve that can adjust the flow rate of the hydraulic fluid instead of a switching valve. However, if a proportional valve is simply used, the flow rate of the hydraulic fluid will fluctuate significantly when switching between extension and retraction, and it will take time for the flow rate to stabilize.

[0007] This disclosure provides an asphalt finisher capable of stabilizing the flow rate of hydraulic fluid and expanding and contracting the width of the screed at an appropriate speed. [Means for solving the problem]

[0008] According to one aspect of the present disclosure, an asphalt finisher is provided which is equipped with a screed for leveling paving material while moving in the laying direction, and comprises a screed extension cylinder that extends and retracts in accordance with the supply of hydraulic fluid to move a side frame which is the leveling limit of the screed, and a hydraulic pump that supplies the hydraulic fluid to the screed extension cylinder, and a switching valve for switching the target to which the hydraulic fluid is supplied and a proportional valve for adjusting the flow rate of the hydraulic fluid are provided in the path between the hydraulic pump and the screed extension cylinder. [Effects of the Invention]

[0009] An asphalt finisher according to one embodiment can stabilize the flow rate of hydraulic fluid and extend and retract the width of the screed at an appropriate speed. [Brief explanation of the drawing]

[0010] [Figure 1] This is a side view of an asphalt finisher according to an embodiment. [Figure 2] This is a plan view of an asphalt finisher. [Figure 3] This is a block diagram showing an example configuration of an automatic steering system. [Figure 4] This is a site plan showing the asphalt finisher passing over the road being constructed. [Figure 5]This diagram shows the hydraulic circuit for the left screed extension cylinder. [Figure 6] This is a flowchart showing the control method for a screed extension cylinder. [Modes for carrying out the invention]

[0011] The following describes embodiments for implementing this disclosure with reference to the drawings. In each drawing, the same reference numerals are used for identical components, and redundant explanations may be omitted.

[0012] Figure 1 is a side view of the asphalt finisher 100 according to the embodiment. Figure 2 is a top view of the asphalt finisher 100. The asphalt finisher 100 according to the embodiment is a wheeled asphalt finisher and mainly comprises a tractor 1, a hopper 2, and a screed 3. Hereinafter, the direction of the hopper 2 as seen from the tractor 1 (+X direction) will be considered the front, and the direction of the screed 3 as seen from the tractor 1 (-X direction) will be considered the rear.

[0013] Tractor 1 is a mechanism for moving the asphalt finisher 100. Tractor 1 moves the asphalt finisher 100 by rotating the rear wheels 5 using a rear-wheel hydraulic motor and rotating the front wheels 6 using a front-wheel hydraulic motor. The rear-wheel hydraulic motor and the front-wheel hydraulic motor rotate by receiving hydraulic fluid 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 also be a crawler-type asphalt finisher in which the rear wheels 5 and the front wheels 6 are replaced with left and right crawlers.

[0014] The asphalt finisher 100 includes a controller 50, which is a control unit that controls various components. The controller 50 is, for example, a microcomputer including a processor, memory (volatile memory and non-volatile memory, etc.), and an input / output interface, and is mounted on the tractor 1. Each function of the controller 50 is realized by the processor executing a program stored in the non-volatile memory. However, each function of the controller 50 may be realized not only by software, but also by hardware, or by a combination of hardware and software.

[0015] Hopper 2 is a mechanism for receiving paving material. In the illustrated example, hopper 2 is installed at the front of tractor 1 and opens and closes in the vehicle width direction (Y-axis direction) by a hopper cylinder. The asphalt finisher 100 typically receives paving material (e.g., asphalt mixture) from the bed of a dump truck when hopper 2 is fully open. A dump truck is an example of a transport vehicle for carrying paving material. Figures 1 and 2 illustrate hopper 2 in the fully open state. When the amount of paving material in hopper 2 decreases, hopper 2 is closed, and the paving material that was near the inner wall of hopper 2 is collected in the center of hopper 2. This is so that the conveyor CV in the center of hopper 2 can feed paving material to the rear of tractor 1. The paving material fed to the rear of tractor 1 is spread in the vehicle width direction at the rear of tractor 1 and in front of screed 3 by screw SC. In the illustrated example, screw SC has extension screws connected on both sides. For ease of understanding, Figures 1 and 2 omit the illustration of the paving material inside the hopper 2. Instead, they show the paving material PV spread by the screw SC with a coarse dot pattern, and the newly laid pavement NP leveled by the screed 3 with a fine dot pattern.

[0016] 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 that can expand and contract in the vehicle width direction, and includes a left rear screed 31L and a right rear screed 31R. The rear screed 31 is expanded and contracted in the vehicle width direction by a screed expansion and contraction cylinder 26. Specifically, the left rear screed 31L is expanded and contracted in the vehicle width direction using a left screed expansion and contraction cylinder 26L. The right rear screed 31R is expanded and contracted in the vehicle width direction using a right screed expansion and contraction cylinder 26R. Further, 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 disposed on the left side of the tractor 1 and a right leveling arm 3AR disposed on the right side of the tractor 1.

[0017] A mold board 43 is attached to the front part of the screed 3. The mold board 43 adjusts the amount of the paving material PV staying in front of the screed 3. The paving material PV reaches under the screed 3 through the gap between the lower end of the mold board 43 and the roadbed BS.

[0018] A pair of side frames 32 (left side frame 32L, right side frame 32R) that define 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 in the front-rear direction with a predetermined length at the left end of the rear screed 31. The left side frame 32L is displaced in the vehicle width direction by the expansion and contraction of the left screed expansion and contraction cylinder 26L. The right side frame 32R extends in the front-rear direction with a predetermined length at the right end of the rear screed 31. The right side frame 32R is displaced in the vehicle width direction by the expansion and contraction of the right screed expansion and contraction cylinder 26R.

[0019] Further, an information acquisition device 51, an in-vehicle display device 52, a steering device 53, and a screed expansion and contraction control device 54 are attached to the tractor 1.

[0020] The information acquisition device 51 acquires information regarding the road to be constructed and outputs the acquired information to the controller 50. The information regarding the road to be constructed includes, for example, the width of the road, the change in curvature in the transition section (clothoid section), and the curvature in the arc section. The information acquisition device 51 includes, for example, a front monitoring device 51F, a rear monitoring device 51B, a traveling speed sensor 51S, a positioning device 51P, and a communication device 51T, etc.

[0021] The front monitoring device 51F acquires information in front of the asphalt finisher 100. The front monitoring device 51F can apply a camera or LiDAR that monitors the monitoring range RF in front of the tractor 1. The front monitoring device 51F is attached to the central part of the tractor 1 (for example, the central front part of the cover covering the engine room behind the hopper 2). However, the front monitoring device 51F may be attached to other parts of the asphalt finisher 100. The front monitoring device 51F may be configured by combining a plurality of cameras and a plurality of LiDARs. For example, the LiDAR may include a right front LiDAR attached to the front right side of the tractor 1 and a left front LiDAR attached to the front left side of the tractor 1.

[0022] The rear monitoring device 51B acquires information behind the asphalt finisher 100. The rear monitoring device 51B can apply a camera or LiDAR that monitors the monitoring range RB behind the screed 3. The rear monitoring device 51B is attached to the guide rail 1G that functions as a handrail. However, the rear monitoring device 51B may be attached to the lower part of the driver's seat 1S or other parts of the asphalt finisher 100. Also, the rear monitoring device 51B may be configured 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 rear right side of the tractor 1 and a left rear LiDAR attached to the rear left side of the tractor 1.

[0023] Furthermore, the information acquisition device 51 may include a side monitoring device for monitoring the sides of the asphalt finisher 100. In this case, the side monitoring device comprises a left-side monitoring device and a right-side monitoring device. The left-side monitoring device is, for example, a camera or LiDAR that monitors a monitoring range to the left of the tractor 1, and is mounted on the left end of the top surface of the tractor 1. The right-side monitoring device is, for example, a camera or LiDAR that monitors a monitoring range to the right of the tractor 1, and is mounted on the right end of the top surface of the tractor 1.

[0024] The camera may be either a monocular camera or a stereo camera, and it captures images of the surrounding area to acquire imaging information. The LiDAR measures, for example, the distance between a number of points within the monitoring range and the LiDAR. However, one or both of the forward monitoring device 51F and the rear monitoring device 51B are not limited to cameras or LiDARs, but may also be millimeter-wave radar, laser radar, laser scanners, depth imaging cameras, or laser rangefinders, etc. The same applies to the side monitoring device.

[0025] The forward monitoring device 51F is preferably configured to detect a monitoring range RF that includes the roadbed BS and the features AP located outside the roadbed BS. This is to enable the acquisition of information regarding the width of the road under construction. The same applies to the monitoring range of the lateral monitoring device. In the illustrated example, the monitoring range RF has a width greater than the width of the roadbed BS. Features AP are, for example, paving formwork, L-shaped drainage ditch blocks, curb blocks, or existing pavement.

[0026] The rear-facing monitoring device 51B is preferably configured to detect a monitoring range RB that includes the newly constructed pavement NP and the features AP located outside the newly constructed pavement NP. This is to allow information about the width of the newly constructed pavement NP to be obtained. In the illustrated example, the monitoring range RB has a width greater than the width of the newly constructed pavement NP.

[0027] 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 and is configured to detect the rotational angular velocity and rotation angle of the rear wheels 5, and consequently, the travel speed and travel distance of the asphalt finisher 100.

[0028] The positioning device 51P is configured to measure the position of the asphalt paver 100. For example, the positioning device 51P is a GNSS compass and is configured to measure the position and orientation of the asphalt paver 100. The GNSS compass as the positioning device 51P includes a left GNSS receiver 51PL mounted on pole PL at the rear end of the left leveling arm 3AL and a right GNSS receiver 51PR mounted on pole PL at the rear end of the right leveling arm 3AR.

[0029] However, the positioning device 51P may be a total station. In this case, a reflective prism, which serves as the target for the total station, is attached to the tip of the pole PL. The main body of the total station, which is 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 target it has determined to the controller 50.

[0030] The communication device 51T communicates information between the asphalt finisher 100 and equipment located outside the asphalt finisher 100. In the illustrated example, the communication device 51T is installed in front of the driver's seat 1S and is configured to perform communication via a mobile communication network, a short-range wireless communication network, or a satellite communication network.

[0031] Furthermore, the information acquisition device 51 may also include a steering angle sensor 51R (see Figure 3) for detecting the steering angle of the asphalt finisher 100, and a screed position sensor 51C (see Figure 3) for calculating the position of the side frame 32.

[0032] Furthermore, the information acquisition device 51 may include a monitoring device installed at the construction site, or a monitoring device attached to an aircraft flying above the asphalt finisher 100. A monitoring device installed at the construction site is, for example, a camera, LiDAR, etc., attached to the tip of a pole installed along the road being constructed. A monitoring device attached to an aircraft is, for example, a camera, LiDAR, etc., attached to a multicopter (drone) or airship, etc.

[0033] The in-vehicle display device 52 is configured to display information related to the asphalt finisher 100. In this embodiment, the in-vehicle display device 52 is a liquid crystal display installed in front of the driver's seat 1S. However, the in-vehicle display device 52 may be installed at the left end or right end of the screed 3, etc.

[0034] The steering device 53 is a device for steering the asphalt finisher 100. In this embodiment, the steering device 53 extends and retracts a front wheel steering cylinder located near the front axle. Specifically, the steering device 53 includes a steering electromagnetic control valve that controls the flow rate of hydraulic fluid from the hydraulic pump to the front wheel steering cylinder and the flow rate of hydraulic fluid discharged from the front wheel steering cylinder. The steering electromagnetic control valve controls the inflow and outflow of hydraulic fluid in the front wheel steering cylinder in accordance with the rotation of the steering wheel SH (handle), which is an operating device. Furthermore, the steering electromagnetic control valve is configured to control the inflow and outflow of hydraulic fluid in the front wheel steering cylinder independently of the rotation of the steering wheel SH, in response to a control command from the controller 50. In other words, the controller 50 can automatically control the steering of the asphalt finisher 100 regardless of whether or not the operator operates the steering wheel SH.

[0035] If the asphalt finisher 100 is a crawler-type asphalt finisher, the steering device 53 is configured to control the left and right pairs of crawlers separately. Specifically, the steering device 53 includes a left electromagnetic control valve that controls the flow rate of hydraulic fluid from the hydraulic pump to the left travel hydraulic motor for rotating the left crawler, and a right electromagnetic control valve that controls the flow rate of hydraulic fluid from the hydraulic pump to the right travel hydraulic motor for rotating the right crawler. The left electromagnetic control valve controls the inflow and outflow of hydraulic fluid in the left travel hydraulic motor according to the amount of operation (angle of inclination) of the left operating lever, which is an operating device for operating the left crawler. The left electromagnetic control valve is also configured to control the inflow and outflow of hydraulic fluid in the left travel hydraulic motor in response to a control command from the controller 50, regardless of whether the operator operates the left operating lever. Similarly, the right electromagnetic control valve controls the inflow and outflow of hydraulic fluid in the right travel hydraulic motor according to the amount of operation (angle of inclination) of the right operating lever, which is an operating device for operating the right crawler. Furthermore, the right electromagnetic control valve is configured to control the inflow and outflow of hydraulic fluid in the right travel hydraulic motor in response to a control command from the controller 50, regardless of whether the operator operates the right control lever.

[0036] The screed extension / retraction control device 54 controls the screed extension / retraction cylinder 26 to extend and retract the rear screed 31. Specifically, the screed 3 is equipped with a switching valve 33 that controls the direction of flow of hydraulic fluid from the hydraulic pump to the screed extension / retraction cylinder 26, and a control valve unit 35 that controls the flow rate of hydraulic fluid (see also Figure 5). The screed extension / retraction control device 54 controls the driving of these switching valve 33 and control valve unit 35.

[0037] The screed extension / retraction control device 54 controls the inflow and outflow of hydraulic fluid in the screed extension / retraction cylinder 26 in response to the on and off operation of the screed extension / retraction switch (not shown), which is an operating device. Furthermore, the screed extension / retraction control device 54 is configured to control the inflow and outflow of hydraulic fluid in the screed extension / retraction cylinder 26 independently of the operation of the screed extension / retraction switch, in response to a control command from the controller 50. In other words, the controller 50 can automatically control the extension / retraction amount of the rear screed 31, regardless of whether the operator operates the screed extension / retraction switch. The control of the screed extension / retraction cylinder 26 will be described in detail later.

[0038] Furthermore, the switching valve 33 includes a left switching valve 33L and a right switching valve 33R, and under the control of the screed extension / retraction control device 54, separately controls the extension / retraction of the left rear screed 31L and the right rear screed 31R. The control valve unit 35 includes a left control valve unit 35L and a right control valve unit 35R, and under the control of the screed extension / retraction control device 54, separately controls the flow rate of hydraulic fluid to the left rear screed 31L and the right rear screed 31R. Specifically, the left switching valve 33L and the left control valve unit 35L control the inflow and outflow of hydraulic fluid flowing from the hydraulic pump to the left screed extension / retraction cylinder 26L in response to the operation of the left screed extension / retraction switch (not shown), which is an operating device. In addition, the left switching valve 33L and the left control valve unit 35L control the inflow and outflow of hydraulic fluid flowing from the hydraulic pump to the left screed extension / retraction cylinder 26L in response to a control command from the controller 50, regardless of whether the left screed extension / retraction switch is operated or not. The same applies to the right electromagnetic control valve.

[0039] Next, an example of the configuration of the automatic steering system DS installed in the asphalt finisher 100 will be explained with reference to Figure 3. Figure 3 is a block diagram showing an example of the configuration of the automatic steering system DS.

[0040] The automatic steering system DS mainly consists of a controller 50, a forward monitoring device 51F, a rear monitoring device 51B, a driving speed sensor 51S, a positioning device 51P, a steering angle sensor 51R, a screed position sensor 51C, a communication device 51T, an on-board display device 52, a steering device 53, and a screed extension / retraction control device 54, etc.

[0041] In the example shown in Figure 3, the controller 50 includes a target calculation unit 50a, a steering control unit 50b, a side frame target trajectory calculation unit 50c, and a screed control unit 50d as functional blocks.

[0042] The target calculation unit 50a calculates the target to be used by the steering control unit 50b. The target used by the steering control unit 50b is, for example, the main target trajectory that a predetermined point on the asphalt finisher 100 should follow. The target trajectory is, strictly speaking, a two-dimensional array of multiple target positions. Alternatively, the target used by the steering control unit 50b may be a target position that the predetermined point on the asphalt finisher 100 should reach after a predetermined time has elapsed. The predetermined time is, for example, a few milliseconds, tens of milliseconds, hundreds of milliseconds, or a few seconds.

[0043] The predetermined point of the asphalt finisher 100 is located on the front and rear axes of the tractor 1, and preferably is set to be located in front of the screed 3. For example, the predetermined point is set in the center, front center, or rear center of the tractor 1, hopper 2, or screed 3. In the embodiment of the asphalt finisher 100, the predetermined point is set in the widthwise center of the screed 3 (front screed 30).

[0044] The target calculation unit 50a calculates the main target trajectory that a predetermined point on the screed 3 should follow in the laying direction of the asphalt finisher 100, based on information about the road to be constructed, such as construction data (design data). The main target trajectory is typically calculated before the asphalt finisher 100 starts moving. Therefore, the main target trajectory may be calculated on a server or the like installed in a management center outside the asphalt finisher 100 and then transmitted to the controller 50 via communication.

[0045] The target calculation unit 50a may calculate the main target position as the point that the predetermined point of the screed 3 should reach after a predetermined time has elapsed. In this case, the main target position is repeatedly calculated at a predetermined control cycle while the asphalt finisher 100 is running. For example, when the asphalt finisher 100 is running on a straight section of the road to be constructed, the target calculation unit 50a may calculate the center point in the width direction of the road to be constructed, located a predetermined distance ahead of the current position of the predetermined point of the screed 3, based on information acquired by the forward monitoring device 51F, as the main target position. The predetermined distance is, for example, several centimeters to several tens of centimeters. The target calculation unit 50a can calculate the main target position without acquiring design data. However, the target calculation unit 50a may calculate the main target position based on design data and information acquired by the forward monitoring device 51F. For example, the target calculation unit 50a may correct the main target position calculated based on design data based on information acquired by the forward monitoring device 51F. Furthermore, the target calculation unit 50a may correct the main target position using information acquired by the rearward monitoring device 51B.

[0046] The steering control unit 50b automatically controls the steering of the asphalt finisher 100 to assist the operator.

[0047] In this embodiment, the steering control unit 50b outputs a control command to the steering device 53 so that a predetermined point on the screed 3 follows the main target trajectory calculated by the target calculation unit 50a. Specifically, the steering control unit 50b calculates the current position of the predetermined point on the screed 3 based on the output of the positioning device 51P. For example, if it is determined that the predetermined point deviates to the right from the main target trajectory, the steering control unit 50b outputs a control command to the steering device 53 so that the tractor 1 moves to the left. Similarly, if it is determined that the predetermined point deviates to the left from the main target trajectory, the steering control unit 50b outputs a control command to the steering device 53 so that the asphalt finisher 100 moves to the right.

[0048] Alternatively, the steering control unit 50b may output a control command to the steering device 53 so that a predetermined point on the screed 3 aligns with the target position calculated by the target calculation unit 50a. In this case, the steering control unit 50b may derive the current position of the predetermined point on the screed 3 based on the output of the positioning device 51P, or it may derive the current position of the predetermined point on the screed 3 based on the output of at least one of the rearward monitoring device 51B and the forward monitoring device 51F.

[0049] Next, referring to Figure 4, the function of moving the asphalt finisher 100 along the target trajectory will be explained. Figure 4 is a plan view of the construction site showing the asphalt finisher 100 passing through the straight section SP1, the curved section LC (left curve), and the straight section SP2 of the road RD to be constructed. In Figure 4, the asphalt finisher 100 at the first time point, which is the start of construction, is indicated by reference numeral 100a. The asphalt finisher 100 at the second time point, after a predetermined time has elapsed from the first time point, is indicated by reference numeral 100b. Similarly, the asphalt finisher 100 at the third time point, after a predetermined time has elapsed from the second time point, is indicated by reference numeral 100c, the asphalt finisher 100 at the fourth time point, after a predetermined time has elapsed from the third time point, is indicated by reference numeral 100d, and the asphalt finisher 100 at the fifth time point, after a predetermined time has elapsed from the fourth time point, is indicated by reference numeral 100e. Note that Figure 4 shows a simplified representation of the asphalt finisher 100, including the tractor 1, front screed 30, left rear screed 31L, and right rear screed 31R, for clarity.

[0050] The target calculation unit 50a of the controller 50 calculates the main target trajectory TPS that the predetermined point Q of the screed 3 should follow at the first time point, which is the start of construction. In Figure 4, the predetermined point Q is represented by a triangle, and the main target trajectory TPS is represented by a dashed line. For example, the target calculation unit 50a refers to design data and derives the main target trajectory TPS based on the left boundary line and the right boundary line of the road RD to be constructed. Note that in Figure 4, the center line CP of the road RD is shown by a dashed line. The main target trajectory TPS may also be generated based on a line that bisects the area of ​​the road surface leveled by the screed 3. The area of ​​the road surface is, for example, the area of ​​the road surface leveled when the asphalt finisher 100 moves forward a predetermined distance.

[0051] The steering control unit 50b of the controller 50 calculates the current position of a predetermined point Q on the screed 3 based on the output of the positioning device 51P. The steering control unit 50b then operates the asphalt finisher 100 so that the actual position coordinates of the predetermined point Q match one of the position coordinates that make up the main target trajectory TPS. As a result, the steering control unit 50b moves the predetermined point Q, which was at the position of point Qa at the first time point, to point Qb at the second time point, to point Qc at the third time point, to point Qd at the fourth time point, and to point Qe at the fifth time point.

[0052] Furthermore, during the movement of the asphalt finisher 100, the left side frame 32L at the left end of the left rear screed 31L is controlled to move along the left side frame target trajectory LTP calculated by the controller 50. Similarly, the right side frame 32R at the right end of the right rear screed 31R is controlled to move along the right side frame target trajectory RTP calculated by the controller 50.

[0053] Therefore, the side frame target trajectory calculation unit 50c of the controller 50 shown in Figure 3 calculates the left side frame target trajectory LTP and the right side frame target trajectory RTP even when the tractor 1 is advanced so that a 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 line of the road RD. However, the left side frame target trajectory LTP may be calculated as a line different from the left boundary line depending on the capabilities of the asphalt finisher 100 (for example, the extension limit and extension speed of the screed 3). Similarly, the right side frame target trajectory RTP is basically calculated as a line corresponding to the right boundary line of the road RD. However, the right side frame target trajectory RTP may also be calculated as a line different from the left boundary line depending on the capabilities of the asphalt finisher 100 (for example, the extension limit and extension speed of the screed 3).

[0054] The side frame target trajectory calculation unit 50c can calculate the left side frame target trajectory LTP and the right side frame target trajectory RTP based, for example, on construction data acquired in advance and the position of the asphalt finisher 100 measured by the positioning device 51P. In this case, the side frame target trajectory calculation unit 50c may calculate the left side frame target trajectory LTP and the right side frame target trajectory RTP before construction. Alternatively, the side frame target trajectory calculation unit 50c can also calculate the left side frame target trajectory LTP and the right side frame target trajectory RTP during construction based on detection information detected by the forward monitoring device 51F or the side monitoring device. 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 regarding the left and right boundary lines several meters in front of the asphalt finisher 100. Alternatively, the side frame target trajectory calculation unit 50c may calculate the left side frame target trajectory LTP and the right side frame target trajectory RTP using the construction data, the position of the asphalt finisher 100, and the detection information detected by the forward monitoring device 51F or the side monitoring device.

[0055] The screed control unit 50d of the controller 50 outputs control commands to the screed extension / retraction control device 54 based on the left side frame target trajectory LTP and the right side frame target trajectory RTP calculated by the side frame target trajectory calculation unit 50c, thereby controlling the operation of the screed 3. The screed control unit 50d outputs control commands such that the left side frame 32L of the left rear screed 31L matches the left side frame target trajectory LTP, and the right side frame 32R of the right rear screed 31R matches the right side frame target trajectory RTP.

[0056] For example, if there is a risk that the left side frame 32L will deviate inward from the left side frame target trajectory LTP, the left side frame 32L will be extended to the left. Conversely, if there is a risk that the left side frame 32L will deviate outward from the left side frame target trajectory LTP, the left side frame 32L will be shortened to the right. Alternatively, if there is a risk that the right side frame 32R will deviate inward from the right side frame target trajectory RTP, the right side frame 32R will be extended to the right. Conversely, if there is a risk that the right side frame 32R will deviate outward from the right side frame target trajectory RTP, the right side frame 32R will be shortened to the left. This ensures that the side frame target trajectories (left side frame target trajectory LTP, right side frame target trajectory RTP) and the width of the newly constructed pavement NP (width of screed 3) match.

[0057] Next, we will describe the specific configuration of the hydraulic circuit having a switching valve 33 and a control valve unit 35 for extending and retracting the screed telescopic cylinder 26. Figure 5 shows the hydraulic circuit for the left screed telescopic cylinder 26L. In the following, we will explain using the hydraulic circuit for extending and retracting the left screed telescopic cylinder 26L as an example, as shown in Figure 5, and will omit the explanation of the hydraulic circuit for extending and retracting the right screed telescopic cylinder 26R, which is configured in a similar manner.

[0058] The hydraulic circuit for the left screed telescopic cylinder 26L includes a left switching valve 33L, a check valve 34, and a left control valve unit 35L between the hydraulic pump 25, which is connected to the hydraulic fluid storage tank 24, and the left screed telescopic cylinder 26L. The left control valve unit 35L contains a bidirectional electromagnetic proportional flow valve (hereinafter simply referred to as proportional valve 36), a pressure compensation valve 37, and an drive switching valve 38. The hydraulic circuit also connects a tank 27 for recovering the hydraulic fluid discharged from the left screed telescopic cylinder 26L to the left switching valve 33L.

[0059] The left screed extension cylinder 26L, connected to the hydraulic circuit, is equipped with a piston rod 262 that divides the internal space of the cylinder body 261 into a base-side oil chamber 261a and a rod-side oil chamber 261b. The left rear screed 31L (see Figure 2) is connected to the piston rod 262. As hydraulic fluid is supplied to the base-side oil chamber 261a from the left switching valve 33L, the left screed extension cylinder 26L extends the piston rod 262 toward the tip. As a result, the left side frame 32L of the left rear screed 31L is displaced outward in the width direction of the screed 3. Conversely, as hydraulic fluid is supplied to the rod-side oil chamber 261b from the left control valve unit 35L, the left screed extension cylinder 26L shortens the piston rod 262 toward the base end. As a result, the left side frame 32L of the left rear screed 31L is displaced inward in the width direction of the screed 3.

[0060] The left-hand switching valve 33L has the function of selectively supplying hydraulic fluid to the base-side oil chamber 261a and the rod-side oil chamber 261b of the left screed telescopic cylinder 26L to be supplied, and the function of stopping the supply of hydraulic fluid. One end of the left-hand switching valve 33L is connected to the hydraulic pump 25 via the supply line 251 and to the tank 27 via the discharge line 271. The other end of the left-hand switching valve 33L is connected to the first check valve 341 of the check valve 34 via the first line 336 and to the second check valve 342 of the check valve 34 via the second line 337.

[0061] The supply line 251, discharge line 271, first line 336, and second line 337 are all connected to the body of the left switching valve 33L, and communicate with three switching paths based on the position of the spool 331 as it moves back and forth within the body. The three switching paths are a supply stop section 333 that stops the supply of hydraulic fluid to the left screed telescopic cylinder 26L, a base end supply section 334 that supplies hydraulic fluid to the base end oil chamber 261a of the left screed telescopic cylinder 26L, and a rod side supply section 335 that supplies hydraulic fluid to the rod side oil chamber 261b via the left control valve unit 35L.

[0062] The supply stop unit 333 shuts off the supply line 251 and has an internal path connecting the first line 336 and the second line 337 to the discharge line 271. When the spool 331 is positioned in the supply stop unit 333 by the drive of the electromagnetic coil 332, the left switching valve 33L stops the supply of hydraulic fluid from the hydraulic pump 25 and allows excess pressure of the hydraulic fluid to be released through the first line 336 and the second line 337. This stops the supply of hydraulic fluid to the left screed telescopic cylinder 26L and allows the position of the piston rod 262 to be maintained.

[0063] The base-side supply unit 334 has an internal path that connects the supply line 251 to the first line 336 in a fully open state and the discharge line 271 to the second line 337. When the spool 331 is positioned in the base-side supply unit 334 by the drive of the electromagnetic coil 332, the left switching valve 33L can supply hydraulic fluid from the hydraulic pump 25 to the base-side oil chamber 261a. The left switching valve 33L can also discharge the hydraulic fluid in the rod-side oil chamber 261b, which flows through the left control valve unit 35L, to the tank 27. As a result, the piston rod 262 of the left screed telescopic cylinder 26L extends.

[0064] The rod-side supply unit 335 has an internal path that connects the supply line 251 to the second line 337 in a fully open state and the discharge line 271 to the first line 336. When the spool 331 is positioned in the rod-side supply unit 335 by the drive of the electromagnetic coil 332, the left switching valve 33L can supply hydraulic fluid from the hydraulic pump 25 to the rod-side oil chamber 261b via the left control valve unit 35L. The left switching valve 33L can also discharge the hydraulic fluid from the base-side oil chamber 261a to the tank 27. As a result, the piston rod 262 of the left screed extension cylinder 26L is shortened. The left switching valve 33L can define the direction of hydraulic fluid flow by continuously positioning the spool 331 in either the base-side supply unit 334 or the rod-side supply unit 335 based on the power supply from the screed extension control device 54.

[0065] The check valve 34 has the function of preventing backflow in the flow direction of the hydraulic fluid switched by the left switching valve 33L. The check valve 34 is a double check valve that includes a first check valve 341 connected to the first line 336 and a second check valve 342 connected to the second line 337. The first check valve 341 allows the hydraulic fluid supplied from the left switching valve 33L to the base end oil chamber 261a to pass through. The second check valve 342 allows the hydraulic fluid supplied from the left switching valve 33L to the rod side oil chamber 261b via the left control valve unit 35L to pass through. In addition, the first check valve 341 and the second check valve 342 allow the leaked hydraulic fluid from the left switching valve 33L to flow to the discharge line 271 when the supply of hydraulic fluid is stopped.

[0066] Furthermore, a branch line 391 is provided in the first line 336 between the first check valve 341 and the base end oil chamber 261a, which branches off from the first line 336 and connects to the discharge line 271. A relief valve 39 is installed in this branch line 391.

[0067] The relief valve 39 is normally closed, but is configured to open the flow path of the branch line 391 when a set pressure is reached. By opening the relief valve 39 when the pressure of the hydraulic fluid on the base end oil chamber 261a side is high, some of the hydraulic fluid in the base end oil chamber 261a can be directly discharged to the tank 27 to reduce the pressure.

[0068] The left control valve unit 35L controls the extension and retraction speed of the left screed telescopic cylinder 26L by linearly changing the flow rate of the hydraulic fluid. The left control valve unit 35L is configured as a structure integrating a proportional valve 36, a pressure compensation valve 37, and a drive switching valve 38. However, it is not limited to this configuration, and the pressure compensation valve 37 and the drive switching valve 38 may each be installed as separate devices.

[0069] The left control valve unit 35L is installed in the second line 337 and controls the flow rate of hydraulic fluid in the supply and discharge of the rod-side oil chamber 261b. In the left screed telescopic cylinder 26L, the amount of hydraulic fluid supplied to the rod-side oil chamber 261b is smaller, resulting in less hydraulic fluid pressure loss. However, the left control valve unit 35L may also be installed in the first line 336 and control the flow rate of hydraulic fluid in the supply and discharge of the base-side oil chamber 261a. Alternatively, the left control valve unit 35L may be installed in both the first line 336 and the second line 337 and control the flow rate of hydraulic fluid in each.

[0070] The proportional valve 36 of the left control valve unit 35L moves the valve body 361 inside the main body relative to the electromagnetic coil 362. The proportional valve 36 moves the valve body 361 between a closed state 363 in which the flow path inside the main body is completely closed and an open state 364 in which the flow path inside the main body is completely open. The valve body 361 may be a spool or another valve body such as a butterfly valve. The valve body 361 linearly changes the opening area of ​​the flow path in proportion to the amount of current supplied to the electromagnetic coil 362. As a result, the proportional valve 36 can discharge hydraulic fluid at a flow rate corresponding to the position of the valve body 361.

[0071] The proportional valve 36 has two hydraulic fluid ports, one of which is connected to line 365 and the other to line 366. This proportional valve 36 is a bidirectional flow valve that can selectively perform two patterns: one in which hydraulic fluid flows into one port and out through the other, and another in which hydraulic fluid flows into the other port and out through the first. Each of lines 365 and 366 is connected to a pressure compensation valve 37.

[0072] Lines 365 and 366 are connected to one end of the pressure compensation valve 37. The other end of the pressure compensation valve 37 is connected to the second line 337 and the cylinder line 376, which is connected to the rod-side oil chamber 261b of the left screed telescopic cylinder 26L. The pressure compensation valve 37 has the function of maintaining a constant differential pressure between the pressure of the second line 337 and the pressure of the cylinder line 376. The pressure compensation valve 37 automatically adjusts the flow rate of the hydraulic fluid so that the differential pressure remains constant at the minimum compensation pressure, even if the flow rate of the hydraulic fluid flowing through the line changes.

[0073] The pressure compensation valve 37 includes a spool 371 that is movably arranged within the main body, and an electromagnetic coil 372 that moves the spool 371 forward and backward. The spool 371 moves within a flow path switching section provided in the main body to adjust the opening area of ​​the flow path between the second line 337 and line 365, and also adjusts the opening area of ​​the flow path between the cylinder line 376 and line 366. The flow path switching section has a first opening configuration 373 in which the opening areas of the second line 337 and the cylinder line 376 are the same, a second opening configuration 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 opening configuration 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. However, the spool 371 can adjust the opening area by moving linearly between the first opening configuration 373 and the third opening configuration 375.

[0074] For example, when supplying hydraulic fluid to the rod-side oil chamber 261b, the spool 371 moves between the first opening configuration 373 and the second opening configuration 374 to adjust the differential pressure of the hydraulic fluid to be constant during supply. Conversely, when discharging hydraulic fluid from the rod-side oil chamber 261b, the spool 371 moves between the first opening configuration 373 and the third opening configuration 375 to adjust the differential pressure of the hydraulic fluid to be constant during discharge.

[0075] Meanwhile, the drive switching valve 38 connects the branch line of the second line 337 and the branch line of the cylinder line 376, switching the communication state between the second line 337 and the cylinder line 376. The drive switching valve 38 moves the valve body 381, which is provided inside the main body, between an open state 383 and a closed state 384 by driving the valve body 381 with an electromagnetic coil 382.

[0076] In the open configuration 383, the second line 337 and the cylinder line 376 are in communication. As a result, the left switching valve 33L is in communication with the rod-side oil chamber 261b. For example, when supplying hydraulic fluid from the left switching valve 33L to the rod-side oil chamber 261b, the hydraulic fluid can be circulated without passing through the proportional valve 36 or the pressure compensation valve 37. Conversely, when discharging hydraulic fluid from the rod-side oil chamber 261b to the left switching valve 33L, the hydraulic fluid can also be circulated without passing through the proportional valve 36 or the pressure compensation valve 37.

[0077] On the other hand, in the blocked configuration 384, the second line 337 and the cylinder line 376 are not in communication. Therefore, when supplying hydraulic fluid from the left switching valve 33L to the rod-side oil chamber 261b, the hydraulic fluid can be circulated through the proportional valve 36 and the pressure compensation valve 37, and the flow rate of the hydraulic fluid can be adjusted by the proportional valve 36 to allow it to flow into the rod-side oil chamber 261b. Conversely, when discharging hydraulic fluid from the rod-side oil chamber 261b to the left switching valve 33L, the hydraulic fluid can also be circulated through the proportional valve 36 and the pressure compensation valve 37, and the flow rate of the hydraulic fluid can be adjusted by the proportional valve 36 to allow the hydraulic fluid to be discharged.

[0078] In other words, the drive switching valve 38 is configured to switch between using and not using the proportional valve 36. This drive switching valve 38 allows the left control valve unit 35L to selectively switch between a first mode in which the flow rate of the hydraulic fluid is adjusted by the proportional valve 36, and a second mode in which the hydraulic fluid flows at a constant flow rate without going through the proportional valve 36. In other words, the left control valve unit 35L can perform a first mode in which the extension and retraction speed of the left screed extension cylinder 26L is adjusted by the proportional valve 36, and a second mode in which the extension and retraction speed of the left screed extension cylinder 26L is kept constant at a limit value by the left switching valve 33L.

[0079] The asphalt finisher 100 according to this embodiment is basically configured as described above. Next, the control method for operating the screed extension cylinder 26 will be explained with reference to Figure 6. Figure 6 is a flowchart showing the control method for the screed extension cylinder 26.

[0080] The screed control unit 50d of the controller 50 determines whether or not to adjust the extension / retraction speed of the screed extension / retraction cylinder 26 in the control method of the screed extension / retraction cylinder 26 (step S101). An example of adjusting the extension / retraction speed of the screed extension / retraction cylinder 26 is when the width of the screed 3 is adjusted by automatic control. In automatic control, the screed control unit 50d controls the left screed extension / retraction cylinder 26L based on the left side frame target trajectory LTP and the right screed extension / retraction cylinder 26R based on the right side frame target trajectory RTP. At this time, the screed control unit 50d recognizes the current position of the left side frame 32L based on the screed position sensor 51C and adjusts the extension / retraction speed of the left screed extension / retraction cylinder 26L according to the deviation (position shift) from the left side frame target trajectory LTP. The same applies to the right screed extension / retraction cylinder 26R. Therefore, if the screed control unit 50d determines to adjust the extension / retraction speed of the screed extension / retraction cylinder 26 based on the ON switch of the automatic control switch of the operating device (step S101: YES), it proceeds to step S102.

[0081] Next, the screed control unit 50d confirms the target operating direction of the screed extension cylinder 26 (step S102). The target operating direction is the direction of extension and retraction of the screed extension cylinder 26. For example, if it is a left screed extension cylinder 26L, it extends when moving to the left and retracts when moving to the right. On the other hand, if it is a right screed extension cylinder 26R, it extends when moving to the right and retracts when moving to the left.

[0082] Then, the screed control unit 50d calculates the extension and retraction speed of the screed extension cylinder 26 (step S103). The extension and retraction speed of the screed extension cylinder 26 is calculated based on the deviation so that it becomes slower as the current position of the side frame 32 gets closer to the target position (side frame target trajectory). This makes it possible for the asphalt finisher 100 to accurately position the moving side frame 32 to the target position.

[0083] Furthermore, the screed control unit 50d calculates the power value to be input to the electromagnetic proportional flow valve (proportional valve 36) based on the calculated extension and retraction speed of the screed extension cylinder 26 (step S104). For example, the screed control unit 50d has in advance table information or a function that shows the correspondence between the extension and retraction speed of the screed extension cylinder 26 and the power value, and extracts the power value corresponding to the extension and retraction speed by referring to the table information.

[0084] The screed control unit 50d transmits a control command including a power value to the screed extension / retraction control device 54, which then supplies power of the commanded power value to the electromagnetic proportional flow valve (proportional valve 36) (step S105). At this stage, the screed control unit 50d also operates the switching valve 33 according to the target operating direction to select one of the extension or retraction of the screed extension / retraction cylinder 26, and operates the drive switching valve 38 to shut off the connection between the second line 337 and the cylinder line 376. As a result, the hydraulic fluid passes through the proportional valve 36.

[0085] In the control valve unit 35, the electromagnetic proportional flow valve (proportional valve 36) changes its opening area in response to the supplied power (step S106). For example, when hydraulic fluid is supplied from the hydraulic pump 25 to the rod-side oil chamber 261b, the hydraulic fluid 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 is adjusted in the proportional valve 36.

[0086] The screed extension cylinder 26 extends and retracts at a set extension speed when the hydraulic fluid with the adjusted flow rate is introduced or when the flow rate of the hydraulic fluid is adjusted during discharge (step S107). This allows the screed extension cylinder 26 to move the supporting side frame 32 in the target operating direction.

[0087] The screed control unit 50d determines whether the side frame 32 has reached the target position when the screed extension cylinder 26 is operating (step S108). The determination of whether the side frame 32 has reached the target position may be made, for example, by monitoring the detection information of the screed position sensor 51C, or by monitoring the movement time of the screed extension cylinder 26 and determining when the target time has been reached. If the side frame 32 has not reached the target position (step S108: NO), the process returns to step S102 and the same process is repeated. As a result, if the side frame 32 has not reached the target position, the target operating direction and extension speed are recalculated and the current value is output again, and the current value is output as the side frame 32 approaches the target position. On the other hand, if the side frame 32 has reached the target position (step S108: YES), this processing flow is terminated.

[0088] Furthermore, if automatic control of the width of the screed 3 is not performed in step S101 (step S101: NO), the operation of the screed extension cylinder 26 will be controlled manually by the operator. In this case, the process proceeds to step S109.

[0089] In step S109, the switching valve 33 controls the inflow and outflow of hydraulic fluid to the screed extension cylinder 26 in accordance with the on and off operation of the screed extension switch, which is an operating device. As a result, the screed extension cylinder 26 extends and retracts at a constant speed (limit value of extension and retraction speed), and the width of the screed 3 can be adjusted early according to the operator's feel.

[0090] As described above, in the control method for the screed telescopic cylinder 26, the target operating direction (supply target) is switched by the switching valve 33, and the flow rate of the hydraulic fluid is adjusted by the proportional valve 36, thereby adjusting the extension and retraction speed of the screed telescopic cylinder 26 to an appropriate speed. Furthermore, if it is desired to move the screed telescopic cylinder 26 at a constant extension and retraction speed (limit value), the hydraulic fluid can be supplied directly from the switching valve 33 to the screed telescopic cylinder 26 by preventing the flow of hydraulic fluid to the proportional valve 36 using the drive switching valve 38.

[0091] Furthermore, the switching valve 33 can smoothly switch between extension and retraction, or vice versa, in the screed telescopic cylinder 26 by moving the spool 331 between the base-side supply unit 334 and the rod-side supply unit 335. At this time, the flow of hydraulic fluid is switched smoothly, so the hydraulic fluid can be stabilized early. Therefore, even if the flow rate of hydraulic fluid is adjusted by the proportional valve 36, the flow of hydraulic fluid to the proportional valve 36 may be stopped at the timing of switching the extension and retraction of the screed telescopic cylinder 26, and the switching valve 33 may be used to switch the target operating direction of the hydraulic fluid.

[0092] Furthermore, the asphalt finisher 100 according to this disclosure is not limited to the above-described embodiment and can take various modifications. For example, the hydraulic circuit of the screed extension cylinder 26 can appropriately switch the supply and stop of hydraulic fluid by applying other on-off valves, so it may be configured without a pressure compensation valve 37 or a drive switching valve 38. Also, for example, the proportional valve 36 is not limited to an electromagnetic proportional flow valve, but a proportional valve 36 of another drive type may be applied.

[0093] <Note> The technical concept and effects of this disclosure, as described in the embodiments above, are described below.

[0094] A first aspect of this disclosure is an asphalt finisher 100 equipped with a screed 3 for spreading paving material PV while moving in the laying direction, comprising a screed extension cylinder 26 that expands and contracts in accordance with the supply of hydraulic fluid to move a side frame 32 which is the spreading limit of the screed 3, and a hydraulic pump 25 that supplies hydraulic fluid to the screed extension cylinder 26, wherein a switching valve 33 for switching the target to which the hydraulic fluid is supplied and a proportional valve 36 for adjusting the flow rate of the hydraulic fluid are provided in the path between the hydraulic pump 25 and the screed extension cylinder 26.

[0095] As described above, the asphalt finisher 100 is equipped with a switching valve 33 and a proportional valve 36 between the hydraulic pump 25 and the screed telescopic cylinder 26, allowing the flow of hydraulic fluid to be controlled by the functions of both the switching valve 33 and the proportional valve 36. For example, when switching the extension or retraction of the screed telescopic cylinder 26, the asphalt finisher 100 can stabilize the flow rate of hydraulic fluid by switching the hydraulic fluid using the switching valve 33. Also, when adjusting the extension or retraction speed of the screed telescopic cylinder 26, the asphalt finisher 100 can adjust the flow rate of hydraulic fluid using the proportional valve 36, making it possible to extend or retract the width of the screed at an appropriate speed.

[0096] Furthermore, the proportional valve 36 can adjust the flow rate of hydraulic fluid supplied to the screed extension cylinder 26, as well as the flow rate of hydraulic fluid discharged from the screed extension cylinder 26. As a result, the asphalt finisher 100 can easily adjust the extension and retraction speed of the screed extension cylinder 26, both when it is extended and when it is retracted, using a single proportional valve 36.

[0097] Furthermore, the proportional valve 36 reduces the flow rate of the hydraulic fluid as the side frame 32 approaches the target position, thereby slowing down the extension and retraction speed of the screed extension cylinder 26. As a result, the asphalt finisher 100 can slow down the extension and retraction speed of the screed extension cylinder 26 when it is close to the target position, and can move the side frame 32 to the target position with precision.

[0098] Furthermore, the switching valve 33 circulates the hydraulic fluid at an upper limit of the flow rate of the hydraulic fluid supplied to the screed telescopic cylinder 26, or at an upper limit of the flow rate of the hydraulic fluid discharged from the screed telescopic cylinder 26. This allows the switching valve 33 to circulate a sufficient flow rate of hydraulic fluid, for example, to efficiently switch the extension and retraction of the screed telescopic cylinder 26.

[0099] Furthermore, the asphalt finisher 100 is equipped with a drive switching valve 38 that can switch between a first mode in which hydraulic fluid is circulated from the switching valve 33 or the screed telescopic cylinder 26 to the proportional valve 36, and a second mode in which hydraulic fluid is circulated between the switching valve 33 and the screed telescopic cylinder 26 without going through the proportional valve 36. As a result, the asphalt finisher 100 can easily switch between the first mode and the second mode using the drive switching valve 38.

[0100] Furthermore, the asphalt finisher 100 is equipped with a controller 50 that controls 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 and retraction speed of the screed extension cylinder 26, and switches to the first mode when adjusting the extension and retraction speed of the screed extension cylinder 26, and to the second mode when not adjusting the extension and retraction speed of the screed extension cylinder 26. As a result, the asphalt finisher 100 can appropriately control the extension and retraction speed of the screed extension cylinder 26.

[0101] Furthermore, the asphalt finisher 100 is equipped with a pressure compensation valve 37 that maintains a constant differential pressure between the pressure of the hydraulic fluid flowing into the proportional valve 36 and the pressure of the hydraulic fluid flowing out of the proportional valve 36. This allows the asphalt finisher 100 to maintain a constant differential pressure when hydraulic fluid is circulated through the proportional valve 36, thereby enabling stable circulation of the hydraulic fluid.

[0102] Furthermore, the screed telescopic cylinder 26 has a base-side oil chamber 261a and a rod-side oil chamber 261b to which hydraulic fluid is supplied, and the proportional valve 36 is installed in the path between the switching valve 33 and the rod-side oil chamber 261b. As a result, the proportional valve 36 can adjust the flow rate of hydraulic fluid in the rod-side oil chamber 261b, which requires less hydraulic fluid, and reduce the pressure loss of the hydraulic fluid.

[0103] The asphalt finisher 100 according to the embodiments disclosed herein is illustrative and not restrictive in all respects. The embodiments can be modified and improved in various ways without departing from the scope and spirit of the appended claims. The features described in the above embodiments can be combined in any way that is not inconsistent with other configurations. [Explanation of Symbols]

[0104] 3 Screede 25 Hydraulic pump 26 Screed telescopic cylinder 32 Side Frames 33 Switching valve 36 Proportional valve 37 Pressure Compensation Valve 38 Drive switching valve 50 Controllers 100 Asphalt Finisher 261a Proximal oil chamber 261b Rod-side oil chamber PV paving material

Claims

1. An asphalt finisher equipped with a screed for spreading and leveling paving material while moving in the laying direction, A screed extension / retraction cylinder that extends and retracts in conjunction with the supply of hydraulic fluid, thereby moving the side frame which is the limit of the screed's leveling, The system includes a hydraulic pump that supplies the hydraulic fluid to the screed extension cylinder, The path between the hydraulic pump and the screed extension cylinder is provided with a switching valve for switching the target to which the hydraulic fluid is supplied, and a proportional valve for adjusting the flow rate of the hydraulic fluid. Asphalt finisher.

2. The proportional valve is capable of adjusting the flow rate of the hydraulic fluid supplied to the screed extension cylinder, and is also capable of adjusting the flow rate of the hydraulic fluid discharged from the screed extension cylinder. The asphalt finisher according to claim 1.

3. The proportional valve reduces the flow rate of the hydraulic fluid as the side frame approaches the target position, thereby slowing down the extension and retraction speed of the screed extension cylinder. The asphalt finisher according to claim 2.

4. The switching valve circulates the hydraulic fluid at an upper limit of the flow rate of the hydraulic fluid supplied to the screed extension cylinder, or at an upper limit of the flow rate of the hydraulic fluid discharged from the screed extension cylinder. The asphalt finisher according to any one of claims 1 to 3.

5. The drive switching valve is capable of switching between a first mode in which the hydraulic fluid is circulated from the switching valve or the screed extension cylinder to the proportional valve, and a second mode in which the hydraulic fluid is circulated between the switching valve and the screed extension cylinder without going through the proportional valve. The asphalt finisher according to claim 4.

6. The system includes a controller that controls the aforementioned switching valve, the proportional valve, and the drive switching valve, The controller determines whether or not to adjust the extension and retraction speed of the screed extension cylinder, and if the extension and retraction speed of the screed extension cylinder is adjusted, it is in the first configuration, and if the extension and retraction speed of the screed extension cylinder is not adjusted, it is in the second configuration. The asphalt finisher according to claim 5.

7. The system includes a pressure compensation valve that maintains a constant differential pressure between the pressure of the hydraulic fluid flowing into the proportional valve and the pressure of the hydraulic fluid flowing out of the proportional valve. The asphalt finisher according to any one of claims 1 to 3.

8. The screed extension cylinder has a base-side oil chamber and a rod-side oil chamber to which the hydraulic fluid is supplied, The proportional valve is installed in the path between the switching valve and the rod-side oil chamber. The asphalt finisher according to any one of claims 1 to 3.

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