Asphalt finisher

Abstract

This disclosure provides an asphalt finisher capable of improving the precision of steering angle control. [Solution] The asphalt finisher includes a plurality of wheels, including steering wheels, a steering cylinder 54 that adjusts the steering angle of the steering wheels, and a hydraulic pump 55 that supplies hydraulic fluid to the steering cylinder 54. The asphalt finisher also includes a proportional control valve 56p positioned between the hydraulic pump 55 and the steering cylinder 54, which controls the flow rate and direction of the hydraulic fluid supplied to the steering cylinder 54, and a controller that controls the steering angle by controlling the proportional control valve 56p.

Description

Technical Field

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

Background Art

[0002] Conventionally, a wheel-type working machine that controls the steering angle of a steering wheel according to the operation of a handle has been known (see Patent Document 1 below). The working machine described in Patent Document 1 controls the steering angle of the steering wheel by switching the direction of the hydraulic oil supplied to the steering cylinder with a direction switching valve.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When using a direction switching valve for steering angle control as in the working machine described in Patent Document 1 above, there are problems in improving the accuracy of steering angle control.

[0005] The present disclosure provides an asphalt finisher capable of improving the accuracy of steering angle control.

Means for Solving the Problems

[0006] An embodiment of the present disclosure provides an asphalt finisher including a plurality of wheels including a steering wheel, a steering cylinder that adjusts the steering angle of the steering wheel, a hydraulic pump that supplies hydraulic oil to the steering cylinder, a proportional control valve disposed between the hydraulic pump and the steering cylinder that controls the flow rate and direction of the hydraulic oil supplied to the steering cylinder, and a controller that controls the steering angle by controlling the proportional control valve.

Effects of the Invention

[0007] According to the embodiments of this disclosure, an asphalt finisher capable of improving the accuracy of steering angle control can be provided. [Brief explanation of the drawing]

[0008] [Figure 1] This is a side view of an asphalt finisher according to an embodiment of the present disclosure. [Figure 2] Figure 1 is a top view of the asphalt finisher. [Figure 3] This is a diagram showing an example configuration of an automatic steering system. [Figure 4] This is a circuit diagram showing the configuration of the steering mechanism of an automatic steering system. [Figure 5] This is a hydraulic circuit diagram of the steering system. [Figure 6] Figure 4 is a circuit diagram showing a modified example of the steering system. [Figure 7] This is a top view of the construction site. [Figure 8] This is a top view of the construction site. [Figure 9A] This is a top view of the construction site. [Figure 9B] This is a top view of the construction site. [Modes for carrying out the invention]

[0009] Figure 1 is a side view of the asphalt finisher 100 according to the embodiment of this disclosure. Figure 2 is a top view of the asphalt finisher 100.

[0010] In this embodiment, the asphalt finisher 100 is a wheeled asphalt finisher and is equipped with multiple wheels W, including rear wheels 5 and front wheels 6. The front wheels 6 are steering wheels that change the direction of travel of the asphalt finisher 100. The asphalt finisher 100 mainly consists of 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.

[0011] The tractor 1 is a mechanism for moving the asphalt finisher 100. In this embodiment, the 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. However, the front wheels 6 may be driven wheels.

[0012] The asphalt finisher 100 may also be a crawler-type asphalt finisher. In this case, the combination of rear wheels 5 and front wheels 6 is replaced by the combination of left crawler and right crawler.

[0013] The controller 50 is a control device that controls the asphalt paver 100. In this embodiment, the controller 50 is composed of a microcomputer including a CPU, a volatile memory device, and a non-volatile memory device, and is mounted on the tractor 1. Each function of the controller 50 is realized by the CPU executing a program stored in the non-volatile memory device. 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.

[0014] Hopper 2 is a mechanism for receiving paving material. In this embodiment, hopper 2 is installed on the front side of tractor 1 and is configured to open and close in the vehicle width direction (Y-axis direction) by a hopper cylinder. The asphalt finisher 100 usually 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 that carries paving material. Figures 1 and 2 show hopper 2 in the fully open position. 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 side of tractor 1. The paving material fed to the rear side of tractor 1 is spread in the vehicle width direction at the rear side of tractor 1 and in front of screed 3 by screw SC. In this embodiment, screw SC has extension screws connected to the left and right. Figures 1 and 2 omit the illustration of the paving material inside the hopper 2 and show the paving material PV spread by the screw SC with a coarse dot pattern, while the newly laid pavement NP leveled by the screed 3 is shown with a fine dot pattern.

[0015] Screed 3 is a mechanism for spreading and leveling the paving material PV. In this embodiment, screed 3 includes a front screed 30 and a rear screed 31. Front screed 30 includes a left front screed 30L and a right front screed 30R. Rear screed 31 is a screed that can be extended and retracted in the vehicle width direction and includes a left rear screed 31L and a right rear screed 31R. However, rear screed 31 may be a fixed-width screed connected to the left and right sides of front screed 30. Screed 3 is also a floating screed towed by tractor 1 and is connected to tractor 1 via leveling arms 3A. Leveling arms 3A include a left leveling arm 3AL located on the left side of tractor 1 and a right leveling arm 3AR located on the right side of tractor 1.

[0016] A mold board 43 is attached to the front part of the screed 3. The mold board 43 is configured to adjust 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.

[0017] An information acquisition device 51, an in-vehicle display device 52, and a steering device 53 are attached to the tractor 1.

[0018] The information acquisition device 51 is configured to acquire information on the road to be constructed and output the acquired information to the controller 50. The information on 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. In the present embodiment, the information acquisition device 51 includes a front monitoring device 51F, a rear monitoring device 51B, a traveling speed sensor 51S, a positioning device 51P, and a communication device 51T.

[0019] The front monitoring device 51F is configured to monitor the front of the asphalt finisher 100. In the present embodiment, the front monitoring device 51F is a LiDAR that monitors the monitoring range RF in front of the tractor 1 and is attached to the central part of the tractor 1. The central part of the tractor 1 is, for example, the center of the front end of the cover that covers the engine room behind the hopper 2. However, the front monitoring device 51F may be attached to other parts of the asphalt finisher 100 or may be composed of a plurality of LiDARs. When composed of a plurality of LiDARs, the front monitoring device 51F can simultaneously monitor a plurality of non-overlapping monitoring ranges. In this case, the plurality of LiDARs may include a right front LiDAR attached to the right front side of the front end of the tractor 1 and a left front LiDAR attached to the left front side of the front end of the tractor 1. Also, the LiDAR may be attached to the tractor 1 via a bracket or a pole or the like.

[0020] The rear monitoring device 51B is configured to monitor the area behind the asphalt finisher 100. In this embodiment, the rear monitoring device 51B is a LiDAR that monitors the monitoring range RB located behind the screed 3 and is mounted on a guide rail 1G that functions as a handrail. However, the rear monitoring device 51B may also be mounted under the driver's seat 1S or on other parts of the asphalt finisher 100. Furthermore, the rear monitoring device 51B may consist of multiple LiDARs. When composed of multiple LiDARs, the rear monitoring device 51B can simultaneously monitor multiple non-overlapping monitoring ranges. In this case, the multiple LiDARs may include a right rear LiDAR mounted on the right rear end of the tractor 1 and a left rear LiDAR mounted on the left rear end of the tractor 1. The LiDARs may also be mounted on the tractor 1 via brackets or poles.

[0021] The information acquisition device 51 may include a side monitoring device configured to monitor the side of the asphalt finisher 100. In this case, the side monitoring device may include a left-side monitoring device and a right-side monitoring device. The left-side monitoring device may be, for example, a LiDAR that monitors a monitoring range to the left of the tractor 1, mounted in front of the rear wheels 5 and at the left end of the top surface of the tractor 1. The right-side monitoring device may be, for example, a LiDAR that monitors a monitoring range to the right of the tractor 1, mounted in front of the rear wheels 5 and at the right end of the top surface of the tractor 1.

[0022] The LiDAR is configured, for example, to measure the distance between a number of points within the monitoring range and the LiDAR itself. However, at least one of the forward monitoring device 51F and the rear monitoring device 51B may be a monocular camera, stereo camera, millimeter-wave radar, laser radar, laser scanner, depth image camera, or laser rangefinder, etc. The same applies to the side monitoring device.

[0023] The monitoring range RF of the forward monitoring device 51F preferably includes the roadbed BS and the ground structure 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 side monitoring device. In this embodiment, the monitoring range RF has a width greater than the width of the roadbed BS. The ground structure AP is an L-shaped gutter block. The ground structure AP may also be a paving formwork, curb block, or existing pavement, etc.

[0024] The monitoring range RB of the rear monitoring device 51B preferably includes the newly constructed pavement NP and the features AP located outside the newly constructed pavement NP. This is to enable the acquisition of information regarding the width of the newly constructed pavement NP. In this embodiment, the monitoring range RB has a width greater than the width of the newly constructed pavement NP.

[0025] The travel speed sensor 51S is configured to detect the travel speed of the asphalt finisher 100. In this embodiment, 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.

[0026] The positioning device 51P is configured to measure the position of the asphalt finisher 100. In this embodiment, the positioning device 51P is a GNSS compass and is configured to measure the position and orientation of the asphalt finisher 100. The GNSS compass as the positioning device 51P includes a left GNSS receiver 51PL and a right GNSS receiver 51PR, as shown in Figures 1 and 2. The left GNSS receiver 51PL is attached to the upper end of a pole PL that extends vertically upward from the rear end of the left leveling arm 3AL. The right GNSS receiver 51PR is attached to the upper end of a pole PL (invisible) that extends vertically upward from the rear end of the right leveling arm 3AR.

[0027] 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.

[0028] The communication device 51T is configured to control communication between the asphalt finisher 100 and equipment located outside the asphalt finisher 100. In this embodiment, the communication device 51T is installed in front of the driver's seat 1S and is configured to control communication via a mobile communication network, a short-range wireless communication network, or a satellite communication network.

[0029] The information acquisition device 51 may include a steering angle sensor configured to detect the steering angle of the asphalt finisher 100, and a pavement width sensor configured to detect the amount of expansion and contraction of the rear screed 31 and calculate the pavement width.

[0030] 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 LiDAR or monocular camera attached to the tip of a pole installed along the road being constructed. A monitoring device attached to an aircraft is, for example, a LiDAR or monocular camera attached to a multicopter (drone) or airship.

[0031] 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 least one of the left end and right end of the screed 3.

[0032] The steering device 53 is configured to control the steering of the asphalt finisher 100. In this embodiment, the steering device 53 is configured to extend and retract a steering cylinder installed near the front axle. As will be described in detail later, the steering device 53 includes an electromagnetic proportional control valve for steering that controls the flow rate of hydraulic fluid flowing from the hydraulic pump to the steering cylinder and the flow rate of hydraulic fluid discharged from the steering cylinder. The proportional control valve is configured to control the inflow and outflow of hydraulic fluid in the steering cylinder in accordance with the rotation of the steering handle SH (steering wheel) which is an operating device. Furthermore, the proportional control valve is configured to control the inflow and outflow of hydraulic fluid in the steering cylinder independently of the rotation of the steering handle SH, in response to a control command from the controller 50. In other words, the controller 50 can control the steering of the asphalt finisher 100 regardless of whether the driver operates the steering handle SH or not.

[0033] Next, with reference to Figures 3 to 6, an example configuration of the automatic steering system DS installed on the asphalt finisher 100 will be described. Figure 3 is a block diagram showing an example configuration of the automatic steering system DS.

[0034] 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 communication device 51T, an on-board display device 52, and a steering device 53, etc.

[0035] Figure 4 is a schematic circuit diagram showing the configuration of the steering device 53 and the steering mechanism 7. Figure 5 is a hydraulic circuit diagram of the steering device 53. Note that Figure 4 omits the illustration of the hydraulic pump 55, power source 8, hydraulic oil tank 9, etc., as shown in Figure 5.

[0036] As shown in Figure 4, the asphalt finisher 100 is equipped with a steering mechanism 7 that can be operated by a steering device 53 to change the steering angle. The steering angle changed by the steering mechanism 7 is the angle of the steering wheels with respect to the straight-line direction (front-rear axis) of the asphalt finisher 100, i.e., the actual steering angle. The steering wheels of the asphalt finisher 100 are, for example, the front wheels 6.

[0037] The steering system 53 may include, for example, a steering cylinder 54, a hydraulic pump 55, and an automatic steering device 56. Alternatively, the steering system 53 may include, for example, a steering wheel SH and a manual steering device 57. Furthermore, the steering system 53 may have, for example, a steering angle sensor 58 for detecting the steering angle.

[0038] The steering cylinder 54 is, for example, a double-rod type hydraulic cylinder that adjusts the steering angle of the front wheels 6, which are the steering wheels. The steering cylinder 54 has a cylinder tube 54c, a piston 54p, and a rod 54r. The steering cylinder 54 can also be replaced with two single-rod type hydraulic cylinders, one on each side.

[0039] The cylinder tube 54c is a hollow cylindrical member and has through holes at both ends in the direction of the central axis through which the rod 54r is inserted. The piston 54p is housed in the cylinder tube 54c, as shown in Figure 5, and forms left and right oil chambers inside the cylinder tube 54c. The rod 54r is provided integrally with the piston 54p and extends to both the left and right sides of the piston 54p. The rod 54r is provided together with the piston 54p so as to be movable left and right along the central axis of the cylinder tube 54c.

[0040] The hydraulic pump 55 is driven by a power source 8, such as an engine or electric motor, mounted on the asphalt finisher 100, as shown in Figure 5. The hydraulic pump 55 supplies hydraulic fluid from a hydraulic fluid tank 9 mounted on the asphalt finisher 100 to the steering cylinder 54. The hydraulic pump 55 is a variable displacement hydraulic pump whose discharge flow rate can be controlled, for example, by controlling the tilt angle of the swash plate with a regulator.

[0041] The steering mechanism 7 includes, for example, an axle shaft 71, left and right knuckles 72L, 72R, left and right kingpins 73L, 73R, and left and right tie rods 74L, 74R, as shown in Figure 4.

[0042] The axle shaft 71 is mounted, for example, to the body of the asphalt finisher 100 and is located below the hopper 2. The left knuckle 72L is rotatably mounted to the left end of the axle shaft 71 via the left kingpin 73L and supports the left front wheel 6. The right knuckle 72R is rotatably mounted to the right end of the axle shaft 71 via the right kingpin 73R and supports the right front wheel 6.

[0043] One end of the left tie rod 74L is connected to the left knuckle 72L. The other end of the left tie rod 74L is rotatably connected to the tip of a rod 54r that extends to the left from the left end of the cylinder tube 54c of the steering cylinder 54. One end of the right tie rod 74R is connected to the right knuckle 72R. The other end of the right tie rod 74R is rotatably connected to the tip of a rod 54r that extends to the right from the right end of the cylinder tube 54c of the steering cylinder 54.

[0044] With this configuration, when the rod 54r of the steering cylinder 54 moves to the right, the left and right knuckles 72L and 72R rotate counterclockwise around the left and right kingpins 73L and 73R. As a result, the steering angle of the left and right front wheels 6, 6, which are supported by the left and right knuckles 72L and 72R, increases to the left relative to the straight-ahead direction.

[0045] Furthermore, when the rod 54r of the steering cylinder 54 moves to the left, the left and right knuckles 72L and 72R rotate clockwise around the left and right kingpins 73L and 73R. As a result, the steering angle of the left and right front wheels 6, 6, which are supported by the left and right knuckles 72L and 72R, increases to the right relative to the straight-ahead direction.

[0046] The steering handle SH is used to manually control the steering angle of the asphalt finisher 100. The steering handle SH is connected, for example, to the metering device 57m of the manual steering device 57 shown in Figure 5, via a steering column (not shown). When the driver of the asphalt finisher 100 rotates the steering handle SH, the metering device 57m of the manual steering device 57 rotates according to the direction, angle, and speed of rotation of the steering handle SH.

[0047] As shown in Figure 5, the manual steering device 57 is positioned in parallel with the automatic steering device 56 between the hydraulic pump 55 and the steering cylinder 54. For example, the Orbitroll® manufactured by Eaton can be used as the manual steering device 57. The manual steering device 57 controls the flow rate and direction of the hydraulic fluid supplied from the hydraulic pump 55 to the steering cylinder 54 in response to the driver's operation of the steering handle SH.

[0048] As will be explained in more detail later, when the driver operates the steering wheel SH, the controller 50 closes the proportional control valve 56p of the automatic steering device 56 to prioritize manual operation. Closing the proportional control valve 56p blocks the flow path of hydraulic fluid from the hydraulic pump 55 through the automatic steering device 56 to the steering cylinder 54. Closing the proportional control valve 56p also blocks the flow path of hydraulic fluid from the steering cylinder 54 through the automatic steering device 56 to the hydraulic fluid tank 9.

[0049] The manual steering device 57 includes, for example, a directional control valve 57d, a check valve 57c, and a metering device 57m. The manual steering device 57 also has four ports: specifically, a P port connected to the hydraulic pump 55, a T port connected to the hydraulic fluid tank 9, an L port connected to the left oil chamber of the steering cylinder 54, and an R port connected to the right oil chamber of the steering cylinder 54.

[0050] The directional control valve 57d is, for example, a 6-port, 3-position directional control valve. The spool of the directional control valve 57d is in the first position when the steering handle SH is in the neutral position and the metering device 57m is in the neutral position. In the first position of the spool, the directional control valve 57d closes the flow path between the P port and the L port and the R port of the manual steering device 57, and also closes the flow path between the L port and the R port of the manual steering device 57 and the T port.

[0051] Therefore, when the spool of the directional control valve 57d is in the first position, the flow path of hydraulic fluid from the hydraulic pump 55 through the manual steering device 57 to the steering cylinder 54 is blocked by the directional control valve 57d. Similarly, the flow path of hydraulic fluid from the steering cylinder 54 through the manual steering device 57 to the hydraulic fluid tank 9 is blocked by the directional control valve 57d. As a result, when the steering angle is not automatically controlled by the automatic steering device 56 and the spool of the directional control valve 57d is in the first position, the piston 54p and rod 54r of the steering cylinder 54 do not move left or right.

[0052] On the other hand, when the steering handle SH is turned to the left, the metering device 57m is rotated to the left, and the spool of the directional control valve 57d moves to the second position. In the second position of the spool, the directional control valve 57d connects the P port of the manual steering device 57 to the right-hand flow path of the metering device 57m, and also connects the left-hand flow path of the metering device 57m to the L port of the manual steering device 57. In addition, in the second position of the spool, the directional control valve 57d connects the R port and T port of the manual steering device 57.

[0053] Therefore, when the steering handle SH is turned to the left, the hydraulic fluid discharged from the hydraulic pump 55 flows into the left oil chamber of the steering cylinder 54 via the P port, metering device 57m, and L port of the manual steering device 57. At this time, the flow rate of the hydraulic fluid corresponds to the rotation angle of the metering device 57m, i.e., the amount of operation of the steering handle SH. Also, as the pressure of the hydraulic fluid in the left oil chamber of the steering cylinder 54 increases and the piston 54p moves to the right, the hydraulic fluid is pushed out from the right oil chamber of the steering cylinder 54 and returns to the hydraulic fluid tank 9 via the R port and T port of the manual steering device 57.

[0054] As described above, when the steering wheel SH is turned to the left, the hydraulic fluid discharged from the hydraulic pump 55 flows into the left oil chamber of the steering cylinder 54 via the manual steering device 57. Also, the hydraulic fluid that flows out from the right oil chamber of the steering cylinder 54 returns to the hydraulic fluid tank 9 via the manual steering device 57. As a result, the rod 54r of the steering cylinder 54 moves to the right together with the piston 54p, moving the ends of the left and right tie rods 74L and 74R connected to the rod 54r shown in Figure 4 to the right. This causes the left and right knuckles 72L and 72R connected to the left and right tie rods 74L and 74R to rotate counterclockwise around the left and right kingpins 73L and 73R. Consequently, the steering angle of the left and right front wheels 6, 6 supported by the left and right knuckles 72L and 72R increases to the left.

[0055] Furthermore, when the steering handle SH is turned to the right, the metering device 57m is rotated to the right, and the spool of the directional control valve 57d moves to the third position. In the third position of the spool, the directional control valve 57d connects the P port of the manual steering device 57 to the left-side passage of the metering device 57m, and also connects the right-side passage of the metering device 57m to the R port of the manual steering device 57. In addition, in the third position of the spool, the directional control valve 57d connects the L port and the T port of the manual steering device 57.

[0056] Therefore, when the steering handle SH is turned to the right, the hydraulic fluid discharged from the hydraulic pump 55 flows into the right oil chamber of the steering cylinder 54 via the P port, metering device 57m, and R port of the manual steering device 57. At this time, the flow rate of the hydraulic fluid corresponds to the rotation angle of the metering device 57m, i.e., the amount of operation of the steering handle SH. Also, as the pressure of the hydraulic fluid in the right oil chamber of the steering cylinder 54 increases and the piston 54p moves to the left, the hydraulic fluid is pushed out from the left oil chamber of the steering cylinder 54 and returns to the hydraulic fluid tank 9 via the L port and T port of the manual steering device 57.

[0057] As described above, when the steering wheel SH is turned to the right, the hydraulic fluid discharged from the hydraulic pump 55 flows into the right oil chamber of the steering cylinder 54 via the manual steering device 57. Also, the hydraulic fluid that flows out from the left oil chamber of the steering cylinder 54 returns to the hydraulic fluid tank 9 via the manual steering device 57. As a result, the rod 54r of the steering cylinder 54 moves to the left together with the piston 54p, moving the ends of the left and right tie rods 74L and 74R connected to the rod 54r shown in Figure 4 to the left. This causes the left and right knuckles 72L and 72R connected to the left and right tie rods 74L and 74R to rotate clockwise around the left and right kingpins 73L and 73R. Consequently, the steering angle of the left and right front wheels 6, 6 supported by the left and right knuckles 72L and 72R increases to the right.

[0058] As shown in Figure 5, the check valve 57c is installed in the flow path connecting the T port and P port of the manual steering device 57. The check valve 57c blocks the flow of hydraulic fluid from the P port to the T port and allows the flow of hydraulic fluid from the T port to the P port. This makes it possible to change the steering angle by supplying hydraulic fluid to the left and right oil chambers of the steering cylinder 54 by rotating the steering handle SH to rotate the metering device 57m, for example, when the hydraulic pump 55 fails.

[0059] The automatic steering device 56 is arranged in parallel with the manual steering device 57 in the hydraulic fluid path between the hydraulic pump 55 and the steering cylinder 54, for example. When the asphalt paver 100 is automatically operated by the controller 50, the automatic steering device 56 controls the flow rate and direction of the hydraulic fluid supplied from the hydraulic pump 55 to the steering cylinder 54 in response to control commands from the controller 50. As a result, the steering mechanism 7 is automatically operated by the automatic steering device 56, and the steering angle is automatically controlled.

[0060] The automatic steering device 56 includes, for example, a fixed throttle 56f, a proportional control valve 56p, and a check valve 56c, as shown in Figure 5. The automatic steering device 56 also has a P port connected to a hydraulic pump 55 via hydraulic fluid piping and a T port connected to a hydraulic fluid tank 9 via hydraulic fluid piping. The automatic steering device 56 also has an A port connected to the right oil chamber of the steering cylinder 54 via hydraulic fluid piping and a B port connected to the left oil chamber of the steering cylinder 54 via hydraulic fluid piping.

[0061] The fixed throttle 56f restricts the flow path of the hydraulic fluid connecting the P port of the automatic steering device 56 and the P port of the proportional control valve 56p by a predetermined hole diameter, thereby controlling the flow rate of the hydraulic fluid by applying resistance to the hydraulic fluid. This prevents sudden movement of the steering cylinder 54, which is supplied with hydraulic fluid via the automatic steering device 56.

[0062] The proportional control valve 56p is positioned between the hydraulic pump 55 and the steering cylinder 54 and controls the flow rate and direction of the hydraulic fluid supplied to the steering cylinder 54. The proportional control valve 56p is, for example, a 4-port, 3-position electromagnetic proportional direction control valve. Specifically, the proportional control valve 56p has four ports: P port, T port, A port, and B port. Each port of the proportional control valve 56p is connected to the corresponding port of the automatic steering device 56. The automatic steering device 56 can also switch the spool position to a first position, a second position, or a third position by acting a solenoid in response to a control command from the controller 50.

[0063] The proportional control valve 56p moves its spool to a first position, for example, when the driver operates the steering wheel SH during manual driving, or when the controller 50 controls the steering angle and the steering angle is maintained without change during automatic driving. The first position of the spool of the proportional control valve 56p is the position where the P port of the proportional control valve 56p is blocked from the other ports, and the A ports and B ports of the proportional control valve 56p are connected to the T port.

[0064] The hydraulic fluid discharged from the hydraulic pump 55 is introduced through the P port of the automatic steering device 56, passes through the fixed throttle 56f, and flows into the P port of the proportional control valve 56p. When the spool of the proportional control valve 56p is in the first position, the flow of hydraulic fluid into the P port of the proportional control valve 56p is blocked by the spool and does not flow into the steering cylinder 54. In addition, the flow of hydraulic fluid from the steering cylinder 54 to the hydraulic fluid tank 9 via the automatic steering device 56 is blocked by the check valve 56c.

[0065] Furthermore, if the steering handle SH is not operated, the flow of hydraulic fluid from the hydraulic pump 55 to the steering cylinder 54 via the manual steering device 57 is blocked by the manual steering device 57. Similarly, if the steering handle SH is not operated, the flow of hydraulic fluid from the steering cylinder 54 to the hydraulic fluid tank 9 via the manual steering device 57 is blocked by the manual steering device 57. Therefore, when the spool of the proportional control valve 56p is in the first position and the steering handle SH is not operated, the piston 54p and rod 54r of the steering cylinder 54 do not move, and the steering angle of the front wheels 6, which are the steering wheels, is maintained.

[0066] Furthermore, the proportional control valve 56p moves its spool to a second position in response to a control command from the controller 50 to increase the steering angle to the left. The second position of the spool of the proportional control valve 56p is the position where the P port and B port of the proportional control valve 56p are connected, and the A port and T port of the proportional control valve 56p are connected. Also, when the spool is in the second position, the proportional control valve 56p proportionally controls the opening degree of the flow path connecting each port in response to a control command from the controller 50.

[0067] The hydraulic fluid discharged from the hydraulic pump 55 is introduced through the P port of the automatic steering device 56, passes through the fixed throttle 56f, and flows into the P port of the proportional control valve 56p. When the spool of the proportional control valve 56p is in the second position, the hydraulic fluid that has flowed into the P port of the proportional control valve 56p is adjusted to a flow rate corresponding to the opening degree of the proportional control valve 56p and is discharged from the B port of the proportional control valve 56p. Subsequently, the hydraulic fluid passes through the check valve 56c, is discharged from the B port of the automatic steering device 56, and flows into the left oil chamber of the steering cylinder 54.

[0068] As a result, the hydraulic fluid pressure in the left oil chamber of the steering cylinder 54 increases, causing the piston 54p to move to the right and push out the hydraulic fluid from the right oil chamber of the steering cylinder 54. The hydraulic fluid pushed out from the right oil chamber of the steering cylinder 54 returns to the hydraulic fluid tank 9 via port A of the automatic steering device 56, check valve 56c, ports A and T of the proportional control valve 56p, and port T of the automatic steering device 56. The check valve 56c allows the flow of hydraulic fluid from port A of the automatic steering device 56 to port A of the proportional control valve 56p when hydraulic fluid is flowing from port B of the proportional control valve 56p to port B of the automatic steering device 56.

[0069] Therefore, when a control command to increase the steering angle to the left is input from the controller 50 to the proportional control valve 56p, hydraulic fluid flows from the hydraulic pump 55 to the left oil chamber of the steering cylinder 54 via the automatic steering device 56. At the same time, hydraulic fluid flows out from the right oil chamber of the steering cylinder 54 to the hydraulic fluid tank 9 via the automatic steering device 56. As a result, the rod 54r of the steering cylinder 54 moves to the right together with the piston 54p, moving the ends of the left and right tie rods 74L and 74R connected to the rod 54r shown in Figure 4 to the right. This causes the left and right knuckles 72L and 72R connected to the left and right tie rods 74L and 74R to rotate counterclockwise around the left and right kingpins 73L and 73R. Then, the steering angle of the left and right front wheels 6, 6 supported by the left and right knuckles 72L and 72R increases to the left.

[0070] Furthermore, the proportional control valve 56p moves its spool to a third position in response to a control command from the controller 50 to increase the steering angle to the right. The third position of the spool of the proportional control valve 56p is the position where the P port and A port of the proportional control valve 56p are connected, and the B port and T port of the proportional control valve 56p are connected. Also, when the spool is in the third position, the proportional control valve 56p proportionally controls the opening degree of the flow path connecting each port in response to a control command from the controller 50.

[0071] The hydraulic fluid discharged from the hydraulic pump 55 is introduced through the P port of the automatic steering device 56, passes through the fixed throttle 56f, and flows into the P port of the proportional control valve 56p. When the spool of the proportional control valve 56p is in the third position, the hydraulic fluid that has flowed into the P port of the proportional control valve 56p is adjusted to a flow rate corresponding to the opening degree of the proportional control valve 56p and is discharged from the A port of the proportional control valve 56p. Subsequently, the hydraulic fluid passes through the check valve 56c, is discharged from the A port of the automatic steering device 56, and flows into the right oil chamber of the steering cylinder 54.

[0072] As a result, the hydraulic fluid pressure in the right oil chamber of the steering cylinder 54 increases, causing the piston 54p to move to the right and push out the hydraulic fluid from the left oil chamber of the steering cylinder 54. The hydraulic fluid pushed out from the left oil chamber of the steering cylinder 54 returns to the hydraulic fluid tank 9 via the B port of the automatic steering device 56, the check valve 56c, the B and T ports of the proportional control valve 56p, and the T port of the automatic steering device 56. The check valve 56c allows the flow of hydraulic fluid from the B port of the automatic steering device 56 to the B port of the proportional control valve 56p when hydraulic fluid is flowing from the A port of the proportional control valve 56p to the A port of the automatic steering device 56.

[0073] Therefore, when a control command to increase the steering angle to the right is input from the controller 50 to the proportional control valve 56p, hydraulic fluid flows from the hydraulic pump 55 to the right oil chamber of the steering cylinder 54 via the automatic steering device 56. At the same time, hydraulic fluid flows out from the left oil chamber of the steering cylinder 54 to the hydraulic fluid tank 9 via the automatic steering device 56. As a result, the rod 54r of the steering cylinder 54 moves to the left together with the piston 54p, causing the ends of the left and right tie rods 74L and 74R connected to the rod 54r shown in Figure 4 to move to the left. This causes the left and right knuckles 72L and 72R connected to the left and right tie rods 74L and 74R to rotate clockwise around the left and right kingpins 73L and 73R. Then, the steering angle of the left and right front wheels 6, 6 supported by the left and right knuckles 72L and 72R increases to the right.

[0074] As shown in Figure 4, the steering angle sensor 58 detects the steering angle of the front wheels 6, which are the steering wheels. In the example shown in Figure 4, the steering angle sensor 58 is an angle sensor that can detect the steering angle of the front wheels 6 by detecting the angle of the left tie rod 74L relative to the rod 54r. Alternatively, the steering angle sensor 58 may detect the steering angle of the front wheels 6 by detecting the rotation angles of the left and right knuckles 72L and 72R around the left and right kingpins 73L and 73R.

[0075] Figure 6 is a circuit diagram corresponding to Figure 4, showing a modified example of the steering device 53 described above. The steering device 53A shown in Figure 6 differs from the steering device 53 shown in Figure 4 in that it has a steering angle sensor 59 instead of a manual steering device 57. The other components of the steering device 53A are the same as those of the steering device 53 shown in Figure 4, so the same parts are denoted by the same reference numerals and their explanation is omitted.

[0076] The steering angle sensor 59 is installed, for example, on the steering column of the steering wheel SH and detects the steering angle of the steering wheel SH. The steering angle is the rotation angle of the steering wheel SH when it is operated. The steering angle sensor 59 detects the rotation direction and amount of operation of the steering wheel SH as the steering angle. The steering angle sensor 59 may also detect, for example, the angular velocity, angular acceleration, torque, etc., when the steering wheel SH is operated. The steering angle sensor 59 outputs a signal to the controller 50 corresponding to the detected steering angle.

[0077] Next, the controller 50 that controls the steering device 53 or steering device 53A will be described. In the example shown in Figure 3, the controller 50 includes a target calculation unit 50a, a steering control unit 50b, and a display control unit 50c as functional blocks.

[0078] The target calculation unit 50a is configured to calculate a target to be used by the steering control unit 50b. The target used by the steering control unit 50b is, for example, a target trajectory as the trajectory that a predetermined point on the asphalt finisher 100 should trace. The predetermined point is a point that is pre-associated with a predetermined part of the asphalt finisher 100, and is also called a steering reference point or control reference point. However, the predetermined point may be a point that is dynamically associated with a predetermined part of the asphalt finisher 100. Strictly speaking, the target trajectory is a one-dimensional array of a number of target positions. The target positions are points that the predetermined point on the asphalt finisher 100 should reach. Alternatively, the target used by the steering control unit 50b may be a target position as a point that the predetermined point on the asphalt finisher 100 should reach after a predetermined time has elapsed. The predetermined time may be, for example, a few milliseconds, tens of milliseconds, hundreds of milliseconds, or a few seconds.

[0079] In this embodiment, the target calculation unit 50a calculates a target trajectory that a predetermined point in the center of the tractor 1 should follow, based on information about the road to be constructed, such as construction design data. In this case, the target trajectory is typically calculated before the asphalt finisher 100 starts running. Therefore, the target trajectory may be calculated by a server installed in a management center outside the asphalt finisher 100 and then transmitted to the controller 50 via communication. Note that the predetermined point may be a point set in the center of the front end of the hopper 2, rather than a point set in the center of the tractor 1. Also, in the case of a wheeled asphalt finisher, the predetermined point may be a point set at the position of the left front wheel, a point set at the position of the right front wheel, or a point set in the center of the front axle.

[0080] The target calculation unit 50a may calculate a target position as the point that a predetermined point in the center of the tractor 1 should reach after a predetermined time has elapsed. In this case, the target position is repeatedly calculated at a predetermined control cycle while the asphalt finisher 100 is running. For example, 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 in the center of the tractor 1, based on information acquired by the forward monitoring device 51F, as the target position. The predetermined distance is, for example, a few centimeters or tens of centimeters. In this case, the target calculation unit 50a can calculate the target position without acquiring construction design data. However, the target calculation unit 50a may calculate the target position based on construction design data and information acquired by the forward monitoring device 51F. For example, the target calculation unit 50a may correct the target position calculated based on construction design data based on information acquired by the forward monitoring device 51F. The target calculation unit 50a may also utilize information acquired by the rear monitoring device 51B.

[0081] The steering control unit 50b is configured to automatically control the steering of the asphalt finisher 100, independently of any operation of the control device.

[0082] In this embodiment, the steering control unit 50b outputs a control command to the steering device 53 so that a predetermined point in the center of the tractor 1 follows the target trajectory calculated by the target calculation unit 50a. Specifically, the steering control unit 50b derives the current position of the predetermined point in the center of the tractor 1 based on the output of the positioning device 51P. If it determines that the predetermined point is deviating to the right from the 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 left. Similarly, if it determines that the predetermined point is deviating to the left from the 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.

[0083] Alternatively, the steering control unit 50b may output a control command to the steering device 53 to position a predetermined point in the center of the tractor 1 at 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 in the center of the tractor 1 based on the output of the positioning device 51P. Alternatively, the current position of the predetermined point in the center of the tractor 1 may be derived based on the output of at least one of the rear monitoring device 51B and the front monitoring device 51F. In the latter case, the positioning device 51P may be omitted.

[0084] The control commands output by the steering control unit 50b to the steering device 53 or steering device 53A include a steering angle control command for the proportional control valve 56p of the automatic steering device 56. The steering angle control command includes, for example, a control command to increase or decrease the steering angle to the left or right in increments of 0.1 degrees, 1 degree, or several degrees. The steering angle control command also includes, for example, a control command for the spool position and opening degree of the proportional control valve 56p of the automatic steering device 56, i.e., a control command for the direction and flow rate of the hydraulic fluid.

[0085] Next, referring to Figure 7, the function of moving the asphalt finisher 100 along the target trajectory will be explained. Figure 7 is a top view of the construction site showing the asphalt finisher 100 passing through a curved section (left curve) of the road RD to be constructed. In Figure 7, asphalt finisher 100a shows the asphalt finisher 100 at the first time point, which is the start of construction. Asphalt finisher 100b shows the asphalt finisher 100 at the second time point, after a predetermined time has elapsed from the first time point. Similarly, asphalt finisher 100c shows the asphalt finisher 100 at the third time point, after a predetermined time has elapsed from the second time point. Asphalt finisher 100d shows the asphalt finisher 100 at the fourth time point, after a predetermined time has elapsed from the third time point. Asphalt finisher 100e shows the asphalt finisher 100 at the fifth time point, after a predetermined time has elapsed from the fourth time point. Note that, for clarity, Figure 7 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, while omitting the illustration of the hopper 2.

[0086] The target calculation unit 50a of the controller 50 calculates the target trajectory TPT that a predetermined point P in the center of the tractor 1 should follow at the first time point, which is the start of construction. In the example shown in Figure 7, the predetermined point P is represented by "○" and the target trajectory TPT is represented by a dashed line. The target calculation unit 50a refers to the construction design data and derives the centerline CP of the road RD based on the left boundary line LP and the right boundary line RP of the road RD to be constructed. Then, the target calculation unit 50a sets the centerline CP as the target trajectory TPS that a predetermined point Q in the center of the front screed 30 should follow. In the example shown in Figure 7, the predetermined point Q is represented by "△" and the target trajectory TPS is represented by a dashed line. Based on known information, including the distance between the rear wheels 5 and the front wheels 6 of the asphalt finisher 100, and the target trajectory TPS, the target calculation unit 50a calculates the target trajectory TPT that the predetermined point P should follow.

[0087] In the example shown in Figure 7, the left boundary line LP, the right boundary line RP, the centerline CP, the target trajectory TPT that a given point P should follow, and the target trajectory TPS that a given point Q should follow are all derived as one-dimensional arrays of numerous position coordinates. These position coordinates are, for example, coordinates in a reference coordinate system.

[0088] A reference coordinate system is, for example, the World Geodetic System. The World Geodetic System is a three-dimensional Cartesian coordinate system with its origin at the Earth's center of mass. Specifically, the World Geodetic System is an XYZ Cartesian coordinate system with the X-axis passing through the intersection of the Greenwich Meridian and the equator and the origin, the Y-axis passing through the intersection of the 90-degree East longitude meridian and the equator and the origin, and the Z-axis passing through the North Pole and the origin.

[0089] Subsequently, the steering control unit 50b of the controller 50 operates the asphalt finisher 100 so that the actual position coordinates of the predetermined point P coincide with one of the position coordinates that make up the target trajectory TPT. Specifically, the steering control unit 50b derives the current position of the predetermined point P in the center of the tractor 1 based on the output of the positioning device 51P.

[0090] Then, if the predetermined point P is located to the right of the target trajectory TPT, the steering control unit 50b outputs a control command to the proportional control valve 56p of the automatic steering device 56, which constitutes the steering device 53, to increase the steering angle to the left. The proportional control valve 56p then moves the spool to the second position and adjusts the flow path of the hydraulic fluid to an opening proportional to the control command, causing a predetermined amount of hydraulic fluid to flow from the hydraulic pump 55 into the left oil chamber of the steering cylinder 54. As a result, the steering mechanism 7 increases the steering angles of the left and right front wheels 6,6 to the left, causing the asphalt finisher 100 to move to the left while moving forward, and the position of the predetermined point P approaches the target trajectory TPT.

[0091] Conversely, if the predetermined point P is located to the left of the target trajectory TPT, the steering control unit 50b outputs a control command to the proportional control valve 56p of the automatic steering device 56, which constitutes the steering device 53, to increase the steering angle to the right. The proportional control valve 56p then moves the spool to the third position and adjusts the flow path of the hydraulic fluid to an opening proportional to the control command, causing a predetermined amount of hydraulic fluid to flow from the hydraulic pump 55 into the right oil chamber of the steering cylinder 54. As a result, the steering mechanism 7 increases the steering angles of the left and right front wheels 6,6 to the right, causing the asphalt finisher 100 to move to the right while moving forward, and the position of the predetermined point P approaches the target trajectory TPT.

[0092] In this way, the controller 50 controls the steering angle by controlling the proportional control valve 56p. As a result, the controller 50 can position a predetermined point P, which was at the position of point Pa at the first time point, at point Pb at the second time point, and at point Pc at the third time point. Similarly, the controller 50 can position the predetermined point P at point Pd at the fourth time point, and at point Pe at the fifth time point. Consequently, the controller 50 can position a predetermined point Q, which was at the position of point Qa at the first time point, at point Qb at the second time point, and at point Qc at the third time point. Similarly, the controller 50 can position the predetermined point Q at point Qd at the fourth time point, and at point Qe at the fifth time point.

[0093] Furthermore, as shown in Figure 4, if the asphalt finisher 100 is equipped with a steering angle sensor 58 that detects the steering angle, the controller 50 may control the steering angle based on the detection result of the steering angle sensor 58 and a target value for the steering angle.

[0094] Furthermore, as shown in Figure 6, if the asphalt finisher 100 is equipped with a steering angle sensor 59 that detects the steering angle of the steering handle SH, the controller 50 may control the proportional control valve 56p based on the detection result of the steering angle sensor 59. Specifically, the controller 50 can acquire the operating direction and amount of the steering handle SH based on the detection result of the steering angle sensor 59, and output a control command corresponding to that operating direction and amount to the proportional control valve 56p of the automatic steering device 56.

[0095] In the example shown in Figure 7, the left rear screed 31L is extended to the left so that its left end face coincides with the left boundary line LP of the road RD, and the right rear screed 31R is extended to the right so that its right end face coincides with the right boundary line RP of the road RD. The left end face of the left rear screed 31L moves along the left boundary line LP, and the right end face of the right rear screed 31R moves along the right boundary line RP. Therefore, the controller 50 can make the width of the road RD match the width of the newly constructed pavement NP by advancing the tractor 1 so that a predetermined point P in the center of the tractor 1 follows the target trajectory TPT.

[0096] The controller 50 may extend or retract the rear screed 31 while the asphalt finisher 100 is in motion. For example, if the left end face of the left rear screed 31L is likely to deviate from the left boundary line LP into the road RD, the controller 50 may extend the left rear screed 31L to the left. Alternatively, if the right end face of the right rear screed 31R is likely to deviate from the right boundary line RP into the road RD, the controller 50 may extend the right rear screed 31R to the right.

[0097] Furthermore, in the example shown in Figure 7, the steering control unit 50b controls the steering of the asphalt finisher 100 when the asphalt finisher 100 is traveling on a curved section of the road RD. However, the steering control unit 50b may also control the steering of the asphalt finisher 100 when the asphalt finisher 100 is traveling on a straight section of the road RD.

[0098] Next, referring to Figure 8, we will explain the function of moving the asphalt paver 100 while determining the target position in real time. Figure 8 is a top view of the construction site showing the asphalt paver 100 passing through a curved section of the road RD to be constructed. For clarity, as with Figure 7, Figure 8 shows the tractor 1, front screed 30, left rear screed 31L, and right rear screed 31R of the asphalt paver 100 in a simplified manner, while omitting the illustration of the hopper 2.

[0099] In the example shown in Figure 8, the target calculation unit 50a of the controller 50 derives the centerline CP of the road RD to be constructed based on the information acquired by the forward monitoring device 51F. In the example shown in Figure 8, the centerline CP is represented by a dotted line. Specifically, the target calculation unit 50a derives the left boundary line LP and the right boundary line RP of the road RD based on the information acquired by the forward monitoring device 51F, and derives the centerline CP of the road RD based on the left boundary line LP and the right boundary line RP. The information acquired by the forward monitoring device 51F is, for example, the position and orientation of the step difference between the curb block and the roadbed BS. The target calculation unit 50a also derives the current position Pn of a predetermined point P in the center of the tractor 1 and the current position Qn of a predetermined point Q in the center of the front screed 30. Specifically, the target calculation unit 50a derives the current position Pn of the predetermined point P and the current position Qn of the predetermined point Q based on the output of the positioning device 51P. In the example shown in Figure 8, the designated point P is represented by "○" and the designated point Q is represented by "△".

[0100] Then, the target calculation unit 50a calculates the target position Pf, which is the point that a predetermined point P should reach after a predetermined time has elapsed. Specifically, the target calculation unit 50a calculates the target position Qf, which is the point that a predetermined point Q should reach after a predetermined time has elapsed, based on the construction design data and the current position Pn of the predetermined point P. The target calculation unit 50a also calculates the target position Pf based on known information, including the distance between the rear wheels 5 and the front wheels 6 of the asphalt finisher 100, and the target position Qf. Both the target position Pf and the target position Qf are derived as position coordinates. Position coordinates are, for example, coordinates in a reference coordinate system. In the example shown in Figure 8, the target position Pf is represented by a dotted line "○", and the target position Qf is represented by a dotted line "△".

[0101] Subsequently, the steering control unit 50b of the controller 50 operates the asphalt finisher 100 so that the position coordinates of a predetermined point P coincide with the position coordinates of the target position Pf. For example, the steering control unit 50b derives the central axis AX of the asphalt finisher 100 based on the output of the positioning device 51P.

[0102] Then, if the target position Pf is located to the left of the central axis AX, the steering control unit 50b outputs a control command to the proportional control valve 56p of the automatic steering device 56, which constitutes the steering device 53, to increase the steering angle to the left. The proportional control valve 56p then moves the spool to the second position and adjusts the flow path of the hydraulic fluid to an opening proportional to the control command, causing a predetermined amount of hydraulic fluid to flow from the hydraulic pump 55 into the left oil chamber of the steering cylinder 54. As a result, the steering mechanism 7 increases the steering angles of the left and right front wheels 6,6 to the left, causing the asphalt finisher 100 to move to the left while moving forward, and the position of the predetermined point P approaches the target position Pf.

[0103] Conversely, if the target position Pf is located to the right of the central axis AX, the steering control unit 50b outputs a control command to the proportional control valve 56p of the automatic steering device 56, which constitutes the steering device 53, to increase the steering angle to the right. The proportional control valve 56p then moves the spool to the third position and adjusts the flow path of the hydraulic fluid to an opening proportional to the control command, causing a predetermined amount of hydraulic fluid to flow from the hydraulic pump 55 into the right oil chamber of the steering cylinder 54. As a result, the steering mechanism 7 increases the steering angles of the left and right front wheels 6,6 to the right, causing the asphalt finisher 100 to move to the right while moving forward, and the position of the predetermined point P approaches the target position Pf.

[0104] In this way, the controller 50 controls the steering angle by controlling the proportional control valve 56p. As a result, the controller 50 can position a predetermined point P at the target position Pf. Consequently, the controller 50 can position a predetermined point Q at the target position Qf.

[0105] The steering control unit 50b may operate the asphalt finisher 100 so that the position coordinates of a predetermined point Q coincide with the position coordinates of a target position Qf. Alternatively, the steering control unit 50b may operate the asphalt finisher 100 so that the predetermined point Q approaches the center line CP of the road RD. In this case, the steering control unit 50b determines at each predetermined control cycle whether the predetermined point Q is on the center line CP of the road RD, to the right of the center line CP, or to the left of the center line CP. Then, if the steering control unit 50b determines that the point is to the right, it moves the asphalt finisher 100 to the left, and if it determines that the point is to the right, it moves the asphalt finisher 100 to the right.

[0106] In the example shown in Figure 8, the left rear screed 31L is extended to the left so that its left end face coincides with the left boundary line LP of the road RD, and the right rear screed 31R is extended to the right so that its right end face coincides with the right boundary line RP of the road RD. The left end face of the left rear screed 31L moves along the left boundary line LP, and the right end face of the right rear screed 31R moves along the right boundary line RP. Therefore, the controller 50 can make the width of the road RD match the width of the newly constructed pavement NP by advancing the tractor 1 so that a predetermined point P in the center of the tractor 1 follows a target position Pf calculated at each predetermined control cycle.

[0107] The controller 50 may extend or retract the rear screed 31 while the asphalt finisher 100 is in motion. For example, if the left end face of the left rear screed 31L is likely to deviate from the left boundary line LP into the road RD, the controller 50 may extend the left rear screed 31L to the left. Alternatively, if the right end face of the right rear screed 31R is likely to deviate from the right boundary line RP into the road RD, the controller 50 may extend the right rear screed 31R to the right.

[0108] Furthermore, in the example shown in Figure 8, the steering control unit 50b controls the steering of the asphalt finisher 100 when the asphalt finisher 100 is traveling on a curved section of the road RD. However, the steering control unit 50b may also control the steering of the asphalt finisher 100 when the asphalt finisher 100 is traveling on a straight section of the road RD.

[0109] Next, with reference to Figures 9A and 9B, the effects of automatically controlling the movement of the asphalt finisher 100 by the steering device 53 will be explained. Figures 9A and 9B are top views of a construction site showing the asphalt finisher 100 passing through a curved section of the road RD to be constructed. Specifically, Figure 9A shows the movement of the asphalt finisher 100 when automatic steering is performed by the steering device 53. Figure 9B shows the movement of the asphalt finisher 100 when manual steering is performed so that a predetermined point P in the center of the tractor 1 follows the center line CP of the road RD. In the examples shown in Figures 9A and 9B, the predetermined point P in the center of the tractor 1 is represented by "○", and the predetermined point Q in the center of the front screed 30 is represented by "△".

[0110] As shown in Figure 9B, when manual steering is performed so that a predetermined point P follows the center line CP of the road RD, a predetermined point Q in the center of the front screed 30 follows the trajectory PS shown by the dashed line. That is, when the asphalt finisher 100 passes through a curve in the road RD, the distance between the front end of the right side of the tractor 1 and the right boundary line RP of the road RD remains approximately equal to the distance between the front end of the left side of the tractor 1 and the left boundary line LP of the road RD. However, the distance between the front end of the right side of the front screed 30 and the right boundary line RP of the road RD remains smaller than the distance between the front end of the left side of the front screed 30 and the left boundary line LP of the road RD. Therefore, paving material is not laid in the inner area of ​​the curve in the road RD shown by the dot pattern, while conversely, paving material is laid in the outer area of ​​the curve in the road RD shown by the cross pattern, extending beyond the right boundary line RP of the road RD.

[0111] Thus, the driver of the asphalt finisher 100 moves the asphalt finisher 100 so that the tractor 1 is centered in the width direction of the road RD as the asphalt finisher 100 passes through a curve in the road RD. However, even if the asphalt finisher 100 is moved in this way, it is not possible to position the screed 3 in the center in the width direction of the road RD.

[0112] In contrast, as shown in Figures 7 and 9A, the movement of the asphalt paver 100 is automatically controlled by the steering device 53 so that a predetermined point P follows the target trajectory TPT. Then, the predetermined point Q in the center of the front screed 30 follows the center line CP of the road RD, which is shown by the dashed line. That is, when the asphalt paver 100 passes through the curved section of the road RD, the distance between the front end of the right side of the tractor 1 and the right boundary line RP of the road RD remains smaller than the distance between the front end of the left side of the tractor 1 and the left boundary line LP of the road RD. However, the distance between the front end of the right side of the front screed 30 and the right boundary line RP of the road RD remains approximately equal to the distance between the front end of the left side of the front screed 30 and the left boundary line LP of the road RD. Therefore, the paving material is reliably laid in the inner area of ​​the curved section of the road RD, and the paving material is not laid beyond the right boundary line RP of the road RD. In other words, the asphalt finisher 100 can match the width of the road RD being worked on with the width of the new pavement NP, even in curved sections of the road RD.

[0113] In this way, the controller 50 moves the asphalt paver 100 so that the tractor 1 approaches the edge of the road RD in the width direction when the asphalt paver 100 passes through a curved section of the road RD. As a result, the screed 3 can be positioned in the center of the road RD in the width direction.

[0114] As described above, the asphalt finisher 100 according to the embodiment of this disclosure comprises a tractor 1, a hopper 2, a conveyor CV, a screw SC, a screed 3, an information acquisition device 51, and a controller 50. The hopper 2 is installed in front of the tractor 1 to receive paving material. The conveyor CV feeds the paving material in the hopper 2 to the rear of the tractor 1. The screw SC spreads the paving material fed by the conveyor CV at the rear of the tractor 1. The screed 3 levels the paving material spread by the screw SC at the rear of the screw SC. The information acquisition device 51 acquires information about the road to be constructed. The controller 50 is a control device that controls the movement of the tractor 1 based on the target trajectory TPT or target position Pf or Qf determined by the information about the road to be constructed acquired by the information acquisition device 51.

[0115] This configuration allows the asphalt finisher 100 to properly lay the pavement along the road RD to be constructed.

[0116] Furthermore, as mentioned above, the conventional work machine described in Patent Document 1 uses a directional control valve that controls the steering cylinder in response to a signal from a controller to steer the steering wheels. In the automated control of the asphalt finisher 100 of this embodiment, for example, the steering angle may be increased or decreased to the left or right in finer control units than manual operation of the steering handle SH, for example, in units of 0.1 degrees, 1 degree, or several degrees.

[0117] The directional control valve in the conventional work machine described above adjusts the flow rate of the hydraulic fluid by switching the flow path between a fully open state and a fully closed state. Therefore, if the directional control valve of the conventional work machine described above is used for automated control, it may not be possible to achieve the steering angle resolution required for the automated control of this embodiment. Consequently, the conventional work machine described above has a challenge in improving the accuracy of steering angle control. In addition, in the conventional work machine described above, the repeated fine steering angle control described above may lead to frequent opening and closing of the directional control valve, potentially increasing the load on the directional control valve.

[0118] In contrast, the asphalt finisher 100 according to this embodiment includes a plurality of wheels W, including front wheels 6,6 which are steering wheels, a steering cylinder 54 that adjusts the steering angle of the steering wheels, and a hydraulic pump 55 that supplies hydraulic fluid to the steering cylinder 54. The asphalt finisher 100 also includes a proportional control valve 56p and a controller 50. The proportional control valve 56p is positioned between the hydraulic pump 55 and the steering cylinder 54 and controls the flow rate and direction of the hydraulic fluid supplied to the steering cylinder 54. The controller 50 controls the steering angle by controlling the proportional control valve 56p.

[0119] This configuration enables improved accuracy in steering angle control of the asphalt finisher 100. Specifically, in the automated control of the asphalt finisher 100, the flow rate of hydraulic fluid supplied to the steering cylinder 54 can be proportionally controlled by the proportional control valve 56p in accordance with the steering angle control command from the controller 50. Therefore, the flow rate of hydraulic fluid supplied to the steering cylinder 54 can be precisely controlled by the proportional control valve 56p, and the steering cylinder 54 can control the steering angle in small angular units. This enables continuous steering and allows for fine and smooth steering. Consequently, the asphalt finisher 100 of this embodiment enables improved accuracy in steering angle control and improves the accuracy of following the target path in automated control. Furthermore, even with fine steering angle control, repeated opening and closing of the proportional control valve 56p is suppressed, reducing the load on the proportional control valve 56p.

[0120] Furthermore, the asphalt finisher 100 according to this embodiment includes a steering handle SH used for manual control of the steering angle, and a manual steering device 57 arranged in parallel with a proportional control valve 56p between the hydraulic pump 55 and the steering cylinder 54. The manual steering device 57 controls the flow rate and direction of the hydraulic fluid supplied from the hydraulic pump 55 to the steering cylinder 54 in response to the operation of the steering handle SH. The controller 50 closes the proportional control valve 56p when the steering handle SH is operated to prioritize manual operation.

[0121] This configuration allows for not only automated control of the steering angle using the proportional control valve 56p, but also manual operation by the driver to change the steering angle by operating the steering wheel SH. Furthermore, the proportional control valve 56p and the manual steering device 57 are connected in parallel between the hydraulic pump 55 and the steering cylinder 54. This reduces the pressure loss of the hydraulic fluid supplied from the hydraulic pump 55 to the steering cylinder 54 compared to when they are connected in series. In addition, the influence of one of the proportional control valve 56p or the manual steering device 57 on the other is suppressed, improving the redundancy of the steering device 53. Moreover, as shown in the steering device 53A of Figure 6, the manual steering device 57 of the steering device 53 can be replaced with a steering angle sensor 59.

[0122] Specifically, the asphalt finisher 100 may further include a steering handle SH used for manual control of the steering angle, and a steering angle sensor 59 for detecting the steering angle of the steering handle SH, as shown in Figure 6. In this case, the controller 50 controls the proportional control valve 56p based on the detection result of the steering angle sensor 59, as described above.

[0123] This configuration simplifies the device configuration by omitting the manual steering device 57, while improving the accuracy of steering angle control of the asphalt finisher 100 in automated steering angle control.

[0124] Furthermore, the asphalt finisher 100 according to this embodiment is further equipped with a steering angle sensor 58 for detecting the steering angle, and the controller 50 controls the steering angle based on the detection result of the steering angle sensor 58 and a target value for the steering angle.

[0125] This configuration enables feedback control of the steering angle, further improving the accuracy of steering angle control for the asphalt finisher 100.

[0126] As shown in Figure 7 or Figure 8, the road RD to be constructed curves to the left. In this case, the controller 50 may be configured to set the target trajectory TPT or target position Pf outside (to the right of) the center (centerline CP) of the road RD to be constructed in the curved portion of the road RD to be constructed. The target trajectory TPT is, for example, the target trajectory that a predetermined point P in the center of the tractor 1 should follow, and the target position Pf is the point that the predetermined point P should reach after a predetermined time has elapsed.

[0127] The controller 50 may be configured to set the target trajectory TPT or target position Pf so that the widthwise center of the road RD to be constructed coincides with the widthwise center of the screed 3. For example, the target calculation unit 50a of the controller 50 may be configured to set the target trajectory TPT or target position Pf so that the trajectory drawn by a predetermined point Q in the center of the front screed 30 coincides with the centerline CP of the road RD, as shown in Figure 7.

[0128] With this configuration, the controller 50 can match the width of the road RD with the width of the newly constructed pavement NP, even when the asphalt paver 100 passes through curved sections as well as straight sections of the road RD.

[0129] The controller 50 may be configured to set the target trajectory TPT or target position Pf such that at least one end of the screed 3 coincides with a feature. For example, as shown in Figure 7, the target calculation unit 50a of the controller 50 may set the target trajectory TPT or target position Pf such that the left end of the screed 3 coincides with the left boundary line LP of the road RD, and the right end of the screed 3 coincides with the right boundary line RP of the road RD. Alternatively, the target calculation unit 50a of the controller 50 may set the target trajectory TPT or target position Pf such that the left end of the screed 3 coincides with the left boundary line LP of the road RD. Alternatively, the target calculation unit 50a of the controller 50 may set the target trajectory TPT or target position Pf such that the right end of the screed 3 coincides with the right boundary line RP of the road RD.

[0130] Furthermore, the controller 50 may be configured to set the target trajectory TPT or target position Pf based on the distance in the longitudinal direction between a predetermined point P, which serves as the steering reference point, and the screed 3. For example, the controller 50 may be configured to set the target trajectory TPT or target position Pf based on the distance in the longitudinal direction between a predetermined point P and a predetermined point Q in the center of the front screed 30.

[0131] Furthermore, the controller 50 may be configured to set the target trajectory TPS or target position Qf based on the longitudinal distance between a predetermined point P, which serves as the steering reference point, and the screed 3. For example, the controller 50 may be configured to set the target trajectory TPS or target position Qf based on the longitudinal distance between a predetermined point P and a predetermined point Q in the center of the front screed 30. The target trajectory TPS is, for example, the target trajectory that the predetermined point Q in the center of the front screed 30 should follow, and the target position Qf is the point that the predetermined point Q should reach after a predetermined time has elapsed.

[0132] The controller 50 may be configured to control the movement of the tractor 1 so that the asphalt paver 100 moves along a preset target trajectory TPT. Specifically, the controller 50 may be configured to control the movement of the tractor 1 so that the asphalt paver 100 moves along a target trajectory TPT set before the asphalt paver 100 starts moving. However, the controller 50 may be configured to control the movement of the tractor 1 so that the asphalt paver 100 moves along a target trajectory TPT calculated in real time.

[0133] This configuration allows the controller 50 to easily and reliably control the movement of the tractor 1 appropriately.

[0134] The information acquisition device 51 may be an imaging device or a communication device 51T. The imaging device may be a LIDAR, monocular camera, stereo camera, or depth image camera, etc.

[0135] Preferred embodiments of the present invention have been described above. However, the present invention is not limited to the embodiments described above. Various modifications or substitutions can be applied to the embodiments described above without departing from the scope of the present invention. Furthermore, each of the features described with reference to the embodiments described above may be combined as appropriate, as long as they do not conflict technically. [Explanation of Symbols]

[0136] 5 Rear wheel (wheel) 6. Front wheels (steering wheels / wheels) 50 Controllers 54 Steering Cylinder 55 Hydraulic pump 56p Proportional control valve 57 Manual steering system 58. Steering angle sensor 59 Steering angle sensor 100 Asphalt Finisher SH Steering Wheel W wheels

Claims

1. Multiple wheels, including the steering wheel, A steering cylinder for adjusting the steering angle of the steering wheel, A hydraulic pump that supplies hydraulic fluid to the steering cylinder, A proportional control valve is positioned between the hydraulic pump and the steering cylinder to control the flow rate and direction of the hydraulic fluid supplied to the steering cylinder, The system includes a controller that controls the steering angle by controlling the proportional control valve, Asphalt finisher.

2. A steering wheel used for manually controlling the steering angle, The system further comprises a manual steering device, which is arranged in parallel with the proportional control valve between the hydraulic pump and the steering cylinder, and controls the flow rate and direction of the hydraulic fluid supplied from the hydraulic pump to the steering cylinder in response to the operation of the steering handle, The controller closes the proportional control valve when the steering wheel is operated, thereby prioritizing manual operation. The asphalt finisher according to claim 1.

3. A steering wheel used for manually controlling the steering angle, The system further comprises a steering angle sensor for detecting the steering angle of the steering wheel, The controller controls the proportional control valve based on the detection result of the steering angle sensor. The asphalt finisher according to claim 1.

4. The system further includes a steering angle sensor for detecting the aforementioned steering angle, The controller controls the steering angle based on the detection result of the steering angle sensor and the target value of the steering angle. The asphalt finisher according to claim 1.

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