ASPHALTFERTIGER

Description

Technical Field

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

[0002] An asphalt finisher including a tractor, a hopper, a conveyor that conveys a paving material in the hopper to a rear side of the tractor, a screw that spreads out the paving material conveyed by the conveyor, and a screed that spreads and levels the paving material behind the screw is known (refer to PTL 1). In addition, PTL 2 discloses a front wheel drive mechanism for road machinery including a hydraulic motor for front wheel drive, in which a hydraulic pressure supplied to a motor is controlled. PTL 3 discloses a front wheel drive force control device for a four-wheel drive asphalt finisher configured to detect and feed back a changing front wheel load, control a pressure of a front wheel drive pump, and increase traction force.

[0003] The asphalt finisher constructs the asphalt pavement while receiving the paving material from a cargo bed of a dump truck adjacent to the front to the hopper.Citation ListPatent Literature

[0004] [PTL 1] Japanese Unexamined Patent Publication No. 2020-63650 [PTL 2] Japanese Utility Model No. S64-14204 [PTL 3] Japanese Utility Model No. H04-77609 Summary of InventionTechnical Problem

[0005] However, although the amount of the paving material in the hopper is relatively large at the start of loading from the cargo bed of the dump truck, the amount of the paving material gradually decreases as the construction progresses. Therefore, as the amount of the paving material in the hopper disposed in a front portion of the tractor is reduced, the front wheel load on the tractor is reduced. As a result, since the frictional force between the front wheel and the ground (roadbed) becomes relatively small, there is a possibility that the driving force of the front wheel becomes larger than the frictional force. Therefore, there is a possibility that the roadbed is dug and the roadbed is damaged by causing the front wheel to slip.

[0006] Therefore, it is an object of the present invention to provide a technique capable of suppressing damage to a roadbed during construction of asphalt pavement.Solution to Problem

[0007] According to an embodiment of the present disclosure, in order to achieve the above-described object, there is provided an asphalt finisher including a tractor, a hopper installed on a front side of the tractor, and that receives a paving material, a conveyor that conveys the paving material in the hopper to a rear side of the tractor, a screw that spreads out the paving material conveyed by the conveyor on the rear side of the tractor, a screed that spreads and levels the paving material spread out by the screw on a rear side of the screw, and a control unit that controls a driving force of a front wheel of the tractor based on a weight of the paving material in the hopper. The asphalt finisher further includes a retaining plate that is a plate-shaped member for preventing the paving material, which is fed out in a vehicle width direction by the screw, from being scattered in front of the screw, a paving material weight acquisition unit configured to estimate the weight of the paving material inside the hopper, and a space recognition device configured to acquire data for monitoring a state of the paving material in the hopper. The control unit is configured to control the driving force of the front wheel based on an estimation result of the weight provided by the estimation unit. The paving material acquisition unit is configured to estimate the weight based on an output of the space recognition device. A volume of the paving material in the hopper is estimated in consideration of an open / closed state of the hopper based on the output of the space recognition device, and the weight is estimated based on the estimated volume.Advantageous Effects of Invention

[0008] According to the above-described embodiment, damage to the roadbed during the construction of the asphalt pavement can be suppressed.Brief Description of Drawings

[0009] Fig. 1A is a schematic view of an asphalt finisher. Fig. 1B is a schematic view of the asphalt finisher. Fig. 2 is a functional block diagram illustrating an example of a configuration of a controller. Fig. 3 is a hydraulic circuit diagram illustrating an example of a configuration of a hydraulic system of the asphalt finisher. Fig. 4 is a graph illustrating an example of a method of controlling the driving force of a front wheel. Fig. 5A is a front view illustrating a state of a paving material inside the hopper. Fig. 5B is a front view illustrating a state of the paving material inside the hopper. Fig. 5C is a front view illustrating a state of the paving material inside the hopper. Fig. 5D is a front view illustrating a state of the paving material inside the hopper. Description of Embodiments

[0010] Hereinafter, embodiments will be described with reference to the drawings.[Overall Configuration]

[0011] First, an overall configuration of an asphalt finisher 100 according to the present embodiment will be described with reference to Figs. 1A and 1B.

[0012] Figs. 1A and 1B are views illustrating an example of the asphalt finisher 100 according to the present embodiment. Specifically, Fig. 1A is a left side view of the asphalt finisher 100, and Fig. 1B is a top view of the asphalt finisher 100.

[0013] In Fig. 1A, the asphalt finisher 100 is disposed such that each of the vehicle length direction, the vehicle width direction, and the vehicle height direction thereof correspond to the X-axis direction, the Y-axis direction, and the Z-axis direction. Specifically, the front side in the vehicle length direction, that is, the front direction of the asphalt finisher 100 corresponds to the X-axis positive direction (+X side), and the rear side in the vehicle length direction, that is, the rear direction of the asphalt finisher 100 corresponds to the X-axis negative direction (-X side). In addition, the left side in the vehicle width direction, that is, the left direction of the asphalt finisher 100 corresponds to the Y-axis positive direction (+Y side), and the right side in the vehicle width direction, that is, the right direction of the asphalt finisher 100 corresponds to the Y-axis negative direction (-Y side). In addition, the upper side in the vehicle height direction, that is, the upper direction of the asphalt finisher 100 corresponds to the Z-axis positive direction (+Z side), and the lower side in the vehicle height direction, that is, the lower direction of the asphalt finisher 100 corresponds to the Z-axis negative direction (-Z side).

[0014] As illustrated in Figs. 1A and 1B, the asphalt finisher 100 is provided with a tractor 1, a hopper 2, a conveyor CV, a screw SC, and a screed 3.

[0015] The tractor 1 corresponds to the main body of the asphalt finisher 100 and causes the asphalt finisher 100 to travel. The tractor 1 includes a rear wheel 5 and a front wheel 6, and the asphalt finisher 100 is caused to travel by rotating the rear wheel 5 using a rear wheel traveling motor 20 (refer to Fig. 3) and rotating the front wheel 6 using a front wheel traveling motor 22 (refer to Fig. 3).

[0016] The tractor 1 may be provided with a crawler instead of the wheels (rear wheel 5 and front wheel 6).

[0017] In addition, as illustrated in Fig. 1A, a driver's seat is provided on an upper portion of the tractor 1. The operator can operate the asphalt finisher in the driver's seat on the upper portion of the tractor 1.

[0018] In addition, as illustrated in Figs. 1A and 1B, for example, a controller 50 is mounted on the tractor 1.

[0019] The controller 50 controls the asphalt finisher 100.

[0020] The function of the controller 50 may be achieved by any hardware or a combination of any hardware and software. The controller 50 is configured to include mainly a computer including, for example, a central processing unit (CPU), a memory device such as a random access memory (RAM), a non-volatile auxiliary storage device such as a read only memory (ROM), and an interface device for input / output to and from the outside. For example, the controller 50 achieves various functions by loading a program installed in the auxiliary storage device into the memory device and causing the CPU to execute the program.

[0021] For example, the controller 50 may control the discharge amount of various hydraulic pumps (described later) that supply hydraulic oil for driving the hydraulic actuator. As will be described later, the hydraulic actuator includes various hydraulic cylinders and hydraulic motors.

[0022] In addition, for example, the controller 50 may control the flow of hydraulic oil between the hydraulic actuator and the hydraulic pump.

[0023] The hopper 2 receives the paving material supplied from a cargo bed of the dump truck. The paving material is, for example, an asphalt mixture or the like.

[0024] As illustrated in Figs. 1A and 1B, the hopper 2 is provided in a front portion of the tractor 1. As will be described later, the hopper 2 includes left and right hopper wings 2W (left hopper wing 2WL and right hopper wing 2WR) (refer to Fig. 5A), and is configured such that left and right hopper wings 2W can be opened and closed in the Y-axis direction (vehicle width direction) by a hopper cylinder 24. Normally, the asphalt finisher 100 receives the paving material from the cargo bed of the dump truck with the hopper 2 fully open. In addition, even when the paving material is received from the cargo bed of the dump truck, the asphalt finisher 100 continues traveling while pushing the dump truck forward through a push roller 2b. An operator of the asphalt finisher 100 closes the hopper 2 when the amount of the paving material in the hopper 2 decreases, and collects the paving material near an inner wall of the hopper 2 in a central portion of the hopper 2. As a result, in the asphalt finisher 100, even when the paving material inside the hopper 2 is relatively small, the conveyor CV at the bottom of the central portion of the hopper 2 can maintain a state where the paving material can be conveyed to the rear side of the tractor 1. The paving material conveyed behind the tractor 1 is spread out in the direction of the tractor 1 and in the vehicle width direction in a region in front of the screed 3 by the screw SC.

[0025] Figs. 1A and 1B illustrate the asphalt finisher 100 when the hopper 2 is in a fully open state.

[0026] In addition, a space recognition device CM is mounted on the tractor 1.

[0027] The space recognition device CM is attached to an upper surface of the front portion of the tractor 1, specifically, a front end portion of the driver's seat on the upper portion of the tractor 1, and acquires data for monitoring the state of the paving material in the hopper 2. The space recognition device CM may include, for example, an imaging device capable of imaging the inside of the hopper 2. The imaging device may include, for example, a monocular camera, a stereo camera, a three-dimensional camera, a depth camera, or the like. In addition, the space recognition device CM may include, for example, a distance sensor such as a light detecting and ranging (LIDAR), a millimeter-wave radar, or an ultrasonic sensor. Output data of the space recognition device CM is taken into the controller 50. As a result, the controller 50 can recognize the amount of the paving material in the hopper 2 based on the output data of the space recognition device CM.

[0028] The conveyor CV conveys the paving material in the central portion of the hopper 2 to the rear side of the tractor 1. The conveyor CV is driven by a hydraulic motor (conveyor motor 21C described later) that rotates by receiving a supply of hydraulic oil from a hydraulic pump (conveyor / screw pump 14S described later). Specifically, the conveyor CV is configured to be capable of conveying the paving material in the hopper 2 to the rear side of the tractor 1 through a conveyance passage CP provided in the tractor 1. The conveyance passage CP is a space of a substantially rectangular body formed inside the tractor 1, and has a substantially rectangular inlet OP that opens into the hopper 2 on the front surface of the tractor 1. The conveyor CV includes, for example, two conveyors disposed on each of the left side and the right side with the center of the asphalt finisher 100 (tractor 1) in the vehicle width direction (Y-axis direction) as a reference. The left side conveyor of the two conveyors is configured to convey the paving material toward a left main screw SCLM described later, and the right side conveyor is configured to convey the paving material toward a right main screw SCRM described later.

[0029] As described above, the screw SC spreads out the paving material to be conveyed to the ground behind the tractor 1 by the conveyor CV. The screw SC is driven by a hydraulic motor (screw motor 21S described later) that rotates by receiving a supply of hydraulic oil from a hydraulic pump (conveyor / screw pump 14S described later). The screw SC includes a left main screw SCLM, a right main screw SCRM, a left extension screw SCLE, and a right extension screw SCRE.

[0030] The left main screw SCLM and the right main screw SCRM are disposed so as to be within the width of the tractor 1 in the vehicle width direction. The left extension screw SCLE is connected to the left end portion of the left main screw SCLM, and is disposed so as to protrude to the left side from the left end portion of the tractor 1 in the vehicle width direction (Y-axis direction). The right extension screw SCRE is connected to the right end portion of the right main screw SCRM, and is disposed so as to protrude to the right side from the right end portion of the tractor 1 in the vehicle width direction.

[0031] The screed 3 spreads and levels the spread paving material behind the screw SC. The screed 3 includes a main screed 30 and an expansion and contraction screed 31.

[0032] The main screed 30 includes, for example, a left main screed and a right main screed disposed on the left side and the right side with the center of the asphalt finisher 100 (tractor 1) in the vehicle width direction as a reference. The expansion and contraction screed 31 includes a left expansion and contraction screed 31L and a right expansion and contraction screed 31R. The main screed 30, the left expansion and contraction screed 31L, and the right expansion and contraction screed 31R are disposed to be shifted back and forth so as not to overlap each other in the vehicle length direction (X-axis direction). Specifically, in the vehicle length direction, the left expansion and contraction screed 31L is disposed on the rear side of the main screed 30, and the right expansion and contraction screed 31R is disposed on the rear side of the left expansion and contraction screed 31L.

[0033] The expansion and contraction screed 31 is configured to be expanded and contracted in the vehicle width direction by the screed expansion and contraction cylinder 27. The screed expansion and contraction cylinder 27 is supported by a support portion fixed to a rear surface of a casing of the main screed 30, and is configured such that the expansion and contraction screed 31 can be expanded and contracted in the vehicle width direction. The screed expansion and contraction cylinder 27 includes a left screed expansion and contraction cylinder 27L and a right screed expansion and contraction cylinder 27R. The left screed expansion and contraction cylinder 27L can expand and contract the left expansion and contraction screed 31L to the left side in the vehicle width direction with respect to the main screed 30. The right screed expansion and contraction cylinder 27R can expand and contract the right expansion and contraction screed 31R to the right side in the vehicle width direction with respect to the main screed 30.

[0034] 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 screed 3 is moved up and down together with the leveling arm 3A by the expansion and contraction of a screed lift cylinder 25.

[0035] The leveling arm 3A is configured so that the screed 3 can be connected to the tractor 1. Specifically, in the leveling arm 3A, one end is connected to the screed 3, and the other end is pivotably connected to the tractor 1. The leveling arm 3A includes a left leveling arm 3AL and a right leveling arm 3AR.

[0036] The leveling cylinder 23 is configured to be able to move the front end portion of the leveling arm 3A up and down in order to adjust the spread leveling thickness (pavement thickness) of the paving material. Specifically, as illustrated in Fig. 1A, in the leveling cylinder 23, a cylinder portion may be connected to the tractor 1 and a rod portion may be connected to the front end portion of the leveling arm 3A.

[0037] The front end portion of the leveling arm 3A is slidably supported by the tractor 1. In a case where the pavement thickness is increased, the controller 50 causes hydraulic oil discharged by a hydraulic pump (cylinder pump 14M described later) to flow into a rod-side oil chamber of the leveling cylinder 23, and contracts the leveling cylinder 23 to raise the front end portion of the leveling arm 3A. On the other hand, in the case of reducing the spread leveling thickness, the controller 50 causes the hydraulic oil in the rod-side oil chamber of the leveling cylinder 23 to flow out, and expands the leveling cylinder 23 to lower the front end portion of the leveling arm 3A.

[0038] The screed lift cylinder 25 is used to lift the screed 3 from a state during the construction (hereinafter, "construction state") to a state relatively distant from the ground (hereinafter, "lift-up state"), or to return the screed 3 from the lift-up state to the construction state. As a result, in a situation other than the asphalt pavement construction work, the screed 3 is maintained in the lift-up state relatively distant from the ground (roadbed), and a situation where the screed 3 and the roadbed are damaged by the contact between the screed 3 and the ground can be suppressed. Specifically, as illustrated in Fig. 1A, in the screed lift cylinder 25, a cylinder portion may be connected to the tractor 1 and a rod portion may be connected to the rear end portion of the leveling arm 3A. In a case where the screed 3 is lifted, the controller 50 causes the hydraulic oil discharged by the hydraulic pump (cylinder pump 14M described later) to flow into a rod-side oil chamber of the screed lift cylinder 25. As a result, the screed lift cylinder 25 contracts, the rear end portion of the leveling arm 3A is lifted, and the screed 3 is lifted. On the other hand, in a case where the lifted screed 3 is lowered, the controller 50 allows hydraulic oil in the rod-side oil chamber of the screed lift cylinder 25 to flow out. As a result, the screed lift cylinder 25 is expanded by the weight of the screed 3, the rear end portion of the leveling arm 3A is lowered, and the screed 3 is lowered. Hereinafter, a function of lifting the screed 3 or lowering the lifted screed 3 by using the screed lift cylinder 25 may be referred to as a "screed lift function".

[0039] In addition, the asphalt finisher 100 is provided with a side plate 40, an expansion and contraction moldboard, a screed step 42, and a retaining plate 43.

[0040] The side plate 40 is attached to an outer end portion of the expansion and contraction screed 31 in the vehicle width direction. The side plate 40 includes a left side plate 40L and a right side plate 40R. Specifically, the left side plate 40L is attached to an outer end portion (left end portion) of the left expansion and contraction screed 31L in the vehicle width direction (Y-axis direction), and the right side plate 40R is attached to the outer end portion (right end portion) of the right expansion and contraction screed 31R in the vehicle width direction.

[0041] The expansion and contraction moldboard 41 is a member for adjusting the amount of the paving material remaining in front of the expansion and contraction screed 31 among the paving materials spread out by the screw SC. The expansion and contraction moldboard 41 is configured to be expanded and contracted in the vehicle width direction together with the expansion and contraction screed 31. The side plate 40 is connected to an outer end portion of the expansion and contraction moldboard 41 in the vehicle width direction (Y-axis direction).

[0042] Specifically, the expansion and contraction moldboard 41 is a plate-shaped member extending in the vehicle width direction, and includes a left expansion and contraction moldboard 41L and a right expansion and contraction moldboard 41R. The left side plate 40L is attached to the outer end portion (left end portion) of the left expansion and contraction moldboard 41L in the vehicle width direction, and the right side plate 40R is attached to the outer end (right end portion) of the right expansion and contraction moldboard 41R.

[0043] In addition, the expansion and contraction moldboard 41 is configured so that the height in the Z-axis direction can be adjusted independently of the expansion and contraction screed 31 and the side plate 40. As a result, the asphalt finisher 100 adjusts the size of the gap between the lower end of the expansion and contraction moldboard 41 and the roadbed by moving the expansion and contraction moldboard 41 up and down, and as a result, the amount of the paving material passing through the gap can be adjusted. Therefore, the asphalt finisher 100 can adjust the amount (height) of the paving material remaining in the region behind the expansion and contraction moldboard 41 and in front of the expansion and contraction screed 31 by moving the expansion and contraction moldboard 41 up and down. In addition, the asphalt finisher 100 can adjust the amount of the paving material taken below the expansion and contraction screed 31.

[0044] The screed step 42 is a member used as a scaffold when a worker works behind the screed 3. Specifically, the screed step 42 includes a left screed step 42L, a center screed step 42C, and a right screed step 42R.

[0045] The retaining plate 43 is a plate-shaped member for preventing the paving material, which is fed out in the vehicle width direction by the screw SC, from being scattered in front of the screw SC. The asphalt finisher 100 can appropriately feed the paving material in the vehicle width direction by using the screw SC due to the action of the retaining plate 43. Specifically, the retaining plate 43 includes a left retaining plate 43L and a right retaining plate 43R.[Functional Configuration]

[0046] Next, in addition to Figs. 1A and 1B, a functional configuration of the controller 50 will be described with reference to Fig. 2. Specifically, the functional configuration of the controller 50 regarding the adjustment function of the driving force of the front wheel 6 (hereinafter, "front wheel driving force adjustment function") will be described.

[0047] Fig. 2 is a functional block diagram illustrating an example of the configuration of the controller 50.

[0048] The controller 50 includes a paving material weight acquisition unit 50A and a front wheel driving force control unit 50B. The functions of the paving material weight acquisition unit 50A and the front wheel driving force control unit 50B are achieved, for example, by loading a predetermined program installed in the auxiliary storage device into the memory device and executing the program on the CPU.

[0049] The paving material weight acquisition unit 50A acquires information regarding the weight of the paving material inside the hopper 2. Specifically, the paving material weight acquisition unit 50A may repeat the processing of acquiring information regarding the weight of the paving material inside the hopper 2 at each predetermined control cycle during the operation of the asphalt finisher 100.

[0050] For example, the paving material weight acquisition unit 50A estimates the amount (volume) of the paving material inside the hopper 2 based on the output data taken in from the space recognition device CM. In this case, the paving material weight acquisition unit 50A may estimate the amount (volume) of the paving material inside the hopper 2 in consideration of an open / closed state of the hopper 2, that is, an expansion / contraction state of the hopper cylinder 24. This is because the shape of an accommodating portion of the paving material inside the hopper 2 changes depending on the open / closed state of the hopper 2. The paving material weight acquisition unit 50A may estimate (calculate) the weight of the paving material inside the hopper 2 based on the estimated volume of the paving material inside the hopper 2, the density (mass per unit volume) of the paving material, and the like.

[0051] In addition, the paving material weight acquisition unit 50A may estimate (calculate) the weight of the paving material inside the hopper 2 based on, for example, the output of the load cell or the strain gauge installed in the hopper 2.

[0052] The front wheel driving force control unit 50B (an example of a control unit) performs control to adjust the driving force of the front wheel 6 based on the information regarding the weight of the paving material inside the hopper 2 acquired by the paving material weight acquisition unit 50A. Specifically, the front wheel driving force control unit 50B repeatedly performs the processing regarding the control for adjusting the driving force of the front wheel 6 at each predetermined control cycle, in synchronization with the processing of the paving material weight acquisition unit 50A.

[0053] In a case where the weight of the paving material inside the hopper 2 is relatively large, the front wheel driving force control unit 50B adjusts the driving force of the front wheel 6 to be relatively large. On the other hand, in a case where the weight of the paving material inside the hopper 2 is relatively small, the front wheel driving force control unit 50B adjusts the driving force of the front wheel 6 to be relatively small. As a result, the controller 50 can adjust the driving force of the front wheel 6 according to the magnitude of the weight of the paving material inside the hopper 2, that is, the magnitude of the load acting on the front wheel 6. Therefore, it is possible to suppress a situation where the driving force of the front wheel 6 exceeds the frictional force between the front wheel 6 and the roadbed and the front wheel 6 slips (wheel spin).

[0054] Specifically, the front wheel driving force control unit 50B controls the driving force of the front wheel 6 so as to maintain a target value changed according to the change in the weight of the paving material acquired by the paving material weight acquisition unit 50A while the asphalt finisher 100 (tractor 1) travels. As a result, the controller 50 can be achieved to correspond to the weight of the paving material inside the hopper 2.

[0055] For example, the front wheel driving force control unit 50B may control (adjust) the driving force of the front wheel 6 by outputting a control command to a relief valve RV (described later) and adjusting the pressure of the hydraulic oil supplied to a front wheel traveling motor 22 (described later) that drives the front wheel 6. That is, the front wheel driving force control unit 50B may achieve the adjustment of the driving force of the front wheel 6 with the relief valve RV as a direct control target.

[0056] In addition, for example, the front wheel driving force control unit 50B may output a control command to a front wheel traveling pump 14F described later (specifically, a regulator that adjusts a tilt angle of a swash plate of the front wheel traveling pump 14F), in addition to the relief valve RV. That is, the front wheel driving force control unit 50B may achieve the adjustment of the driving force of the front wheel 6 with the front wheel traveling pump 14F (regulator) as a direct control target, in addition to the relief valve RV. As a result, the front wheel driving force control unit 50B can adjust the angle (hereinafter, "tilt angle") of the swash plate of the front wheel traveling pump 14F, and adjust the pressure of the hydraulic oil supplied to the front wheel traveling motor 22.

[0057] For example, the front wheel driving force control unit 50B may determine a target value for the driving force of the front wheel 6 according to the weight of the paving material inside the hopper 2, and control the controlled variable of the direct control target (relief valve RV and front wheel traveling pump 14F) so as to achieve the determined target value. In addition, the front wheel driving force control unit 50B may control the controlled variable of the direct control target, for example, in accordance with a control rule (refer to Fig. 4 described later) which is defined in advance so as to achieve the target value of the driving force of the front wheel 6 according to the weight of the paving material, and represents the relationship between the weight of the paving material and the controlled variable of the direct control target. As a result, the controller 50 can control the driving force of the front wheel 6 so as to maintain the target value of the driving force of the front wheel 6, which is changed according to the change in the weight of the paving material inside the hopper 2. Therefore, the controller 50 can appropriately control the driving force of the front wheel 6 according to a change in the weight of the paving material inside the hopper 2.[Hydraulic System]

[0058] Next, a hydraulic system mounted on the asphalt finisher 100 will be described with reference to Fig. 3.

[0059] Fig. 3 is a hydraulic circuit diagram illustrating an example of a configuration of the hydraulic system of the asphalt finisher 100.

[0060] The hydraulic system includes a hydraulic source 14, a rear wheel drive unit F1, a conveyor / screw drive unit F2, a front wheel drive unit F3, a steering / compacting device drive unit F4, a leveling unit F5, a hopper drive unit F6, a screed lift unit F7, and a screed expansion and contraction unit F8.

[0061] The hydraulic source 14 sucks the hydraulic oil from a hydraulic oil tank T and supplies the hydraulic oil to various drive units. The hydraulic source 14 includes an engine 14E, a rear wheel traveling pump 14R, a charge pump 14C, a cylinder pump 14M, a conveyor / screw pump 14S, and a front wheel traveling pump 14F.

[0062] The engine 14E is a drive source that drives the rear wheel traveling pump 14R, the charge pump 14C, the cylinder pump 14M, the conveyor / screw pump 14S, and the front wheel traveling pump 14F.

[0063] The rear wheel traveling pump 14R is a variable-capacity hydraulic pump that supplies hydraulic oil for driving to the rear wheel drive unit F1. Specifically, the rear wheel traveling pump 14R may be a swash plate type variable-capacity bidirectional hydraulic pump used in a closed circuit.

[0064] The charge pump 14C is a fixed-capacity hydraulic pump that supplies hydraulic oil for control to the rear wheel drive unit F1.

[0065] The cylinder pump 14M is a variable-capacity hydraulic pump capable of supplying hydraulic oil to each of the steering / compacting device drive unit F4, the leveling unit F5, the hopper drive unit F6, the screed lift unit F7, and the screed expansion and contraction unit F8. The cylinder pump 14M is a swash plate type variable-capacity hydraulic pump, and a discharge amount thereof is controlled so that a discharge pressure becomes constant at a predetermined pressure.

[0066] The conveyor / screw pump 14S is a variable-capacity hydraulic pump that supplies hydraulic oil to the conveyor / screw drive unit F2. Specifically, the conveyor / screw pump 14S may be a swash plate type variable-capacity hydraulic pump.

[0067] The front wheel traveling pump 14F (an example of a hydraulic pump) is a variable-capacity hydraulic pump that supplies hydraulic oil to the front wheel drive unit F3. Specifically, the front wheel traveling pump 14F is a swash plate type variable-capacity hydraulic pump.

[0068] The rear wheel drive unit F1 is configured to be able to drive the rear wheel 5 by using the hydraulic oil supplied from the hydraulic source 14. The rear wheel drive unit F1 includes a left rear wheel traveling motor 20L, a right rear wheel traveling motor 20R, check valves 20La and 20Ra, relief valves 20Lb and 20Rb, and a speed reducer switching valve V0.

[0069] The left rear wheel traveling motor 20L and the right rear wheel traveling motor 20R drive the left and right rear wheels, respectively. Specifically, the left rear wheel traveling motor 20L and the right rear wheel traveling motor 20R may be stepless speed change type hydraulic motors, and may form a closed circuit, that is, a hydro-static transmission (HST) circuit together with the rear wheel traveling pump 14R.

[0070] The check valve 20La maintains the pressure of hydraulic oil in a pipeline C1 connecting a first port ((1) in the drawing) of the rear wheel traveling pump 14R and a second port ((2) in the drawing) of each of the left rear wheel traveling motor 20L and the right rear wheel traveling motor 20R at a predetermined pressure or higher. Specifically, the check valve 20La causes the hydraulic oil discharged by the charge pump 14C to flow into the pipeline C1 in a case where the pressure of the hydraulic oil in the pipeline C1 is lower than the discharge pressure of the charge pump 14C. Similarly, the check valve 20Ra maintains the pressure of hydraulic oil in a pipeline C2 connecting a second port ((2) in the drawing) of the rear wheel traveling pump 14R and a first port ((1) in the drawing) of each of the left rear wheel traveling motor 20L and the right rear wheel traveling motor 20R at a predetermined pressure or higher. Specifically, the check valve 20Ra causes the hydraulic oil discharged by the charge pump 14C to flow into the pipeline C2 in a case where the pressure of the hydraulic oil in the pipeline C2 is lower than the discharge pressure of the charge pump 14C.

[0071] The relief valve 20Lb maintains the pressure of the hydraulic oil in the pipeline C1 to be a predetermined relief pressure or lower. Specifically, the relief valve 20Lb causes the hydraulic oil in the pipeline C1 to flow out to the outside of the closed circuit (for example, the hydraulic oil tank T) in a case where the pressure of the hydraulic oil in the pipeline C1 exceeds the relief pressure. Similarly, the relief valve 20Rb maintains the pressure of the hydraulic oil in the pipeline C2 to be a predetermined relief pressure or lower. Specifically, the relief valve 20Rb causes the hydraulic oil in the pipeline C2 to flow out to the outside of the closed circuit (for example, the hydraulic oil tank T) in a case where the pressure of the hydraulic oil in the pipeline C2 exceeds the relief pressure.

[0072] The speed reducer switching valve V0 switches the reduction ratio of each of the left rear wheel traveling motor 20L and the right rear wheel traveling motor 20R. Specifically, the speed reducer switching valve V0 switches the reduction ratio of each of the left rear wheel traveling motor 20L and the right rear wheel traveling motor 20R using the hydraulic oil discharged by the charge pump 14C in response to a control command from the controller 50.

[0073] The conveyor / screw drive unit F2 is configured to be able to drive the conveyor CV and the screw SC by using the hydraulic oil supplied from the hydraulic source 14. The conveyor / screw drive unit F2 includes a conveyor motor 21C, a screw motor 21S, a conveyor control valve V1C, and a screw control valve V1S.

[0074] Both the conveyor motor 21C and the screw motor 21S are variable-capacity hydraulic motors that constitute an open circuit. The conveyor motor 21C includes a left conveyor motor 21CL and a right conveyor motor 21CR. The screw motor 21S includes a left screw motor 21SL and a right screw motor 21SR. The conveyor control valve V1C includes a left conveyor control valve V1CL and a right conveyor control valve V1CR. The screw control valve V1S includes a left screw control valve V1SL and a right screw control valve V1SR.

[0075] The left conveyor control valve V1CL operates in response to a control command from the controller 50 to cause the hydraulic oil discharged by the conveyor / screw pump 14S to flow into a suction port of the left conveyor motor 21CL and to discharge hydraulic oil flowing out from a discharge port of the left conveyor motor 21CL to the hydraulic oil tank T. The right conveyor control valve V1CR operates in response to a control command from the controller 50 to cause the hydraulic oil discharged by the conveyor / screw pump 14S to flow into a suction port of the right conveyor motor 21CR and to discharge hydraulic oil flowing out from a discharge port of the right conveyor motor 21CR to the hydraulic oil tank T. Similarly, the left screw control valve V1SL operates in response to a control command from the controller 50 to cause the hydraulic oil discharged by the conveyor / screw pump 14S to flow into a suction port of the left screw motor 21SL and to discharge hydraulic oil flowing out from a discharge port of the left screw motor 21SL to the hydraulic oil tank T. The right screw control valve V1SR operates in response to a control command from the controller 50 to cause the hydraulic oil discharged by the conveyor / screw pump 14S to flow into a suction port of the right screw motor 21SR and to discharge hydraulic oil flowing out from a discharge port of the right screw motor 21SR to the hydraulic oil tank T. The hydraulic oil flowing out from the discharge port of each of the left conveyor motor 21CL, the right conveyor motor 21CR, the left screw motor 21SL, and the right screw motor 21SR is discharged to the hydraulic oil tank T through an oil cooler OC.

[0076] The front wheel drive unit F3 is configured to be able to drive the front wheel 6 by using the hydraulic oil supplied from the hydraulic source 14. The front wheel drive unit F3 includes a front wheel traveling motor 22, a front wheel traveling valve V2, and a relief valve RV.

[0077] The front wheel traveling motor 22 (an example of a hydraulic motor) is a fixed-capacity hydraulic motor that constitutes an open circuit. The front wheel traveling motor 22 includes a left front wheel traveling motor 22L for driving the left front wheel 6L (refer to Fig. 5A) of the front wheels 6 and a right front wheel traveling motor 22R for driving the right front wheel 6R (refer to Fig. 5A) of the front wheels 6.

[0078] The front wheel traveling valve V2 operates in response to a control command from the controller 50, and causes the hydraulic oil discharged by the front wheel traveling pump 14F to flow into a suction port of the front wheel traveling motor 22. The front wheel traveling pump 14F supplies the hydraulic oil to each of the left front wheel traveling motor 22L and the right front wheel traveling motor 22R in parallel via the front wheel traveling valve V2.

[0079] The relief valve RV is provided in an oil passage between the front wheel traveling pump 14F and the front wheel traveling valve V2. The relief valve RV is, for example, an electromagnetic relief valve. When the pressure of the hydraulic oil in the oil passage between the front wheel traveling pump 14F and the front wheel traveling motor 22 reaches a predetermined relief pressure, the relief valve RV discharges the hydraulic oil in the oil passage to the hydraulic oil tank T. As a result, the pressure of the hydraulic oil supplied to the front wheel traveling motor 22 can be limited to a predetermined relief pressure or lower.

[0080] The relief pressure of the relief valve RV is variable. Specifically, the controller 50 transmits a control command for designating the setting content (set value) of the relief pressure to the relief valve RV. As a result, the relief valve RV sets (changes) the relief pressure in response to a control command input from the controller 50. As a result, the relief valve RV can maintain the pressure of the hydraulic oil in the oil passage between the front wheel traveling pump 14F and the front wheel traveling motor 22 to be a set relief pressure or lower. Therefore, the controller 50 (front wheel driving force control unit 50B) adjusts the pressure of the hydraulic oil supplied to the front wheel traveling motor 22 by varying the relief pressure of the relief valve RV, and as a result, the driving force of the front wheel 6 can be adjusted.

[0081] The steering / compacting device drive unit F4 is configured to be able to drive a steering device and a compacting device (both not illustrated) by using the hydraulic oil supplied from the hydraulic source 14.

[0082] The steering device is a hydraulic device for steering the front wheel 6. For example, the steering device changes the steering angle of the front wheel 6 by using the hydraulic oil discharged by the cylinder pump 14M in response to an operation of the steering wheel by an operator. In addition, the compacting device is a hydraulic device for compacting the paving material. The compacting device includes a tamper and a vibrator, and operates the tamper and the vibrator by using the hydraulic oil discharged by the cylinder pump 14M.

[0083] The leveling unit F5 is configured so that the pavement thickness can be adjusted by using the hydraulic oil supplied from the hydraulic source 14. The leveling unit F5 includes a leveling cylinder 23, a leveling control valve 33, and a pilot check valve 33P.

[0084] As described above, the leveling cylinder 23 moves the leveling arm 3A up and down in order to adjust the pavement thickness. Specifically, the leveling cylinder 23 is configured to contract when the pavement thickness is increased and to expand when the pavement thickness is decreased. The leveling cylinder 23 includes a left leveling cylinder 23L and a right leveling cylinder 23R.

[0085] The leveling control valve 33 operates in response to a control signal from the controller 50 to control the flow rate and the direction of the flow of the hydraulic oil supplied to the leveling cylinder 23. The leveling control valve 33 includes a left leveling control valve 33L and a right leveling control valve 33R. In a case where the pavement thickness is increased, the left leveling control valve 33L causes the hydraulic oil discharged by the cylinder pump 14M to flow into a rod-side oil chamber of the left leveling cylinder 23L and causes the hydraulic oil flowing out from a head-side oil chamber of the left leveling cylinder 23L to discharge to the hydraulic oil tank T. In this case, the left leveling cylinder 23L contracts, and the left leveling arm 3AL rises. The same applies to the right leveling control valve 33R that contracts the right leveling cylinder 23R. On the other hand, in a case where the pavement thickness is reduced, the left leveling control valve 33L causes the hydraulic oil discharged by the cylinder pump 14M to flow into the head-side oil chamber of the left leveling cylinder 23L and causes the hydraulic oil flowing out from the rod-side oil chamber of the left leveling cylinder 23L to discharge to the hydraulic oil tank T. In this case, the left leveling cylinder 23L expands and the left leveling arm 3AL lowers. The same applies to the right leveling control valve 33R that expands the right leveling cylinder 23R.

[0086] The pilot check valve 33P is configured to prevent the leveling cylinder 23 from moving due to an external force. The pilot check valve 33P includes pilot check valves 33PaL, 33PbL, 33PaR, and 33PbR. For example, in the pilot check valve 33PaL, only in a case where the left leveling control valve 33L operates in response to an operation of the operator and the hydraulic oil discharged by the cylinder pump 14M flows into the head-side oil chamber of the left leveling cylinder 23L, the hydraulic oil in the rod-side oil chamber of the left leveling cylinder 23L is allowed to flow toward the hydraulic oil tank T. In other cases, the pilot check valve 33PaL prohibits the hydraulic oil in the rod-side oil chamber of the left leveling cylinder 23L from flowing toward the hydraulic oil tank T. The same applies to the pilot check valves 33PbL, 33PaR, and 33PbR.

[0087] The hopper drive unit F6 is configured to be able to open and close the hopper 2 by using the hydraulic oil supplied from the hydraulic source 14. The hopper drive unit F6 includes a hopper cylinder 24, a hopper control valve 34, and a pilot check valve 34P.

[0088] The hopper cylinder 24 opens and closes the hopper 2. The hopper cylinder 24 contracts when the hopper 2 is opened and expands when the hopper 2 is closed. The hopper cylinder 24 includes a left hopper cylinder 24L and a right hopper cylinder 24R.

[0089] The hopper control valve 34 operates in response to a control signal from the controller 50 to control the flow rate and the direction of the flow of the hydraulic oil supplied to the hopper cylinder 24. The hopper control valve 34 includes a left hopper control valve 34L and a right hopper control valve 34R. In a case where the hopper 2 is opened, the left hopper control valve 34L causes the hydraulic oil discharged by the cylinder pump 14M to flow into a rod-side oil chamber of the left hopper cylinder 24L and causes the hydraulic oil flowing out from a head-side oil chamber of the left hopper cylinder 24L to discharge to the hydraulic oil tank T. In this case, the left hopper cylinder 24L contracts. In addition, the right hopper control valve 34R causes the hydraulic oil discharged by the cylinder pump 14M to flow into a rod-side oil chamber of the right hopper cylinder 24R and causes the hydraulic oil flowing out from a head-side oil chamber of the right hopper cylinder 24R to discharge to the hydraulic oil tank T. In this case, the right hopper cylinder 24R contracts. On the other hand, in a case where the hopper 2 is closed, the left hopper control valve 34L causes the hydraulic oil discharged by the cylinder pump 14M to flow into the head-side oil chamber of the left hopper cylinder 24L and causes the hydraulic oil flowing out from the rod-side oil chamber of the left hopper cylinder 24L to discharge to the hydraulic oil tank T. In this case, the left hopper cylinder 24L expands. In addition, the right hopper control valve 34R causes the hydraulic oil discharged by the cylinder pump 14M to flow into the head-side oil chamber of the right hopper cylinder 24R and causes the hydraulic oil flowing out from the rod-side oil chamber of the right hopper cylinder 24R to discharge to the hydraulic oil tank T. In this case, the right hopper cylinder 24R expands.

[0090] The pilot check valve 34P is configured to prevent the hopper cylinder 24 from contracting due to the weight of the hopper 2 or the weight of the hopper 2 and the paving material in the hopper 2 and causing the hopper 2 to open. The pilot check valve 34P includes a pilot check valve 34PL and a pilot check valve 34PR. For example, in the pilot check valve 34PL, only in a case where the left hopper control valve 34L operates in response to an operation of the operator and the hydraulic oil discharged by the cylinder pump 14M flows into the rod-side oil chamber of the left hopper cylinder 24L, the hydraulic oil in the head-side oil chamber of the left hopper cylinder 24L is allowed to flow toward the hydraulic oil tank T. In other cases, the pilot check valve 34PL prohibits the hydraulic oil in the head-side oil chamber of the left hopper cylinder 24L from flowing toward the hydraulic oil tank T. The same applies to the pilot check valve 34PR.

[0091] In the hopper drive unit F6, the pilot check valve is not installed between a rod-side oil chamber of the hopper cylinder 24 and the hopper control valve 34. This is because since the weight of the hopper 2 is large, there is a low possibility that the hopper cylinder 24 is unintentionally expanded due to an external force. However, a pilot check valve may be installed between the rod-side oil chamber of the hopper cylinder 24 and the hopper control valve 34.

[0092] The screed lift unit F7 is configured such that the screed 3 can be lifted or the lifted screed can be lowered by using the hydraulic oil supplied from the hydraulic source 14. The screed lift unit F7 includes a screed lift cylinder 25, a screed lift control valve 35, a switching valve 35a, a relief valve 35b, and a switching valve 35c.

[0093] As described above, the screed lift cylinder 25 lifts the screed 3 and lowers the lifted screed 3. Specifically, the screed lift cylinder 25 contracts when the screed 3 is lifted, and expands when the screed 3 is lowered. The screed lift cylinder 25 includes a left screed lift cylinder 25L and a right screed lift cylinder 25R.

[0094] The screed lift control valve 35 operates in response to a control signal from the controller 50 to control the flow rate and the direction of the flow of the hydraulic oil supplied to the screed lift cylinder 25. In a case where the screed 3 is lifted, the screed lift control valve 35 causes the hydraulic oil discharged by the cylinder pump 14M to flow into the rod-side oil chamber of the screed lift cylinder 25. In this case, the switching valve 35a is switched to the first position including the check valve in response to the control signal from the controller 50. As a result, it is possible to prevent the hydraulic oil from flowing back from the rod-side oil chamber of the screed lift cylinder 25 toward the hydraulic oil tank T. The hydraulic oil flowing out from a head-side oil chamber of the screed lift cylinder 25 is discharged to the hydraulic oil tank T without passing through the screed lift control valve 35. In this case, the screed lift cylinder 25 contracts. On the other hand, in a case where the screed 3 is lowered to the ground, the screed lift control valve 35 is not used and is maintained in the state illustrated in Fig. 3. In this case, the switching valve 35a is switched to the second position that does not include the check valve in response to the control signal from the controller 50. As a result, the hydraulic oil in the rod-side oil chamber of the screed lift cylinder 25 can flow out toward the hydraulic oil tank T. Therefore, the screed lift cylinder 25 is expanded by the weight of the screed 3, and the hydraulic oil in the rod-side oil chamber of the screed lift cylinder 25 is discharged to the hydraulic oil tank T through the switching valve 35a and the relief valve 35b.

[0095] The switching valve 35a and the relief valve 35b achieve vertical movement of the screed 3 in accordance with changes in lifting force (that is, a force that the paving material tries to lift the screed 3) generated when the asphalt finisher 100 paves the road while moving. Specifically, when the screed 3 rises due to an increase in lifting force, the screed lift cylinder 25 contracts. In this case, the hydraulic oil discharged by the cylinder pump 14M flows into the rod-side oil chamber of the screed lift cylinder 25 through a pipeline C3, the screed lift control valve 35, and the switching valve 35a. On the other hand, when the screed 3 is lowered due to a decrease in lifting force, the screed lift cylinder 25 is expanded. In this case, the hydraulic oil flowing out from the rod-side oil chamber of the screed lift cylinder 25 is discharged to the hydraulic oil tank T through the switching valve 35a, the screed lift control valve 35, and the relief valve 35b. The switching valve 35c is switched to the first position including the check valve in response to the control signal from the controller 50, when paving the road while the asphalt finisher 100 moves, that is, while the hydraulic device such as a downstream screed expansion and contraction unit F8 is not used. As a result, it is possible to prevent adverse effects on the hydraulic device such as the downstream screed expansion and contraction unit F8. Specifically, this is to prevent the expansion and contraction screed 31, a crown device, a step device (all not illustrated), or the like from unintentionally moving.

[0096] The screed expansion and contraction unit F8 is configured such that the expansion and contraction screed 31 can be expanded and contracted in the vehicle width direction (Y-axis direction) by using the hydraulic oil supplied from the hydraulic source 14. The screed expansion and contraction unit F8 includes a screed expansion and contraction cylinder 27, a screed expansion and contraction control valve 37, a pilot check valve 37P, and a relief valve 37V.

[0097] The screed expansion and contraction control valve 37 operates in response to a control signal from the controller 50 to control the flow rate and the direction of the flow of the hydraulic oil supplied to the screed expansion and contraction cylinder 27. The screed expansion and contraction control valve 37 includes a left screed expansion and contraction control valve 37L and a right screed expansion and contraction control valve 37R.

[0098] In a case where the left expansion and contraction screed 31L is retracted, the left screed expansion and contraction control valve 37L causes the hydraulic oil discharged by the cylinder pump 14M to flow into a rod-side oil chamber of the left screed expansion and contraction cylinder 27L, and causes the hydraulic oil flowing out from a head-side oil chamber of the left screed expansion and contraction cylinder 27L to discharge to the hydraulic oil tank T. In this case, the left screed expansion and contraction cylinder 27L contracts, and the left expansion and contraction screed 31L retracts. The same applies to a case where the right expansion and contraction screed 31R is retracted by the right screed expansion and contraction control valve 37R. On the other hand, in a case where the left expansion and contraction screed 31L is extruded, the left screed expansion and contraction control valve 37L causes the hydraulic oil discharged by the cylinder pump 14M to flow into the head-side oil chamber of the left screed expansion and contraction cylinder 27L, and causes the hydraulic oil flowing out from the rod-side oil chamber of the left screed expansion and contraction cylinder 27L to discharge to the hydraulic oil tank T. In this case, the left screed expansion and contraction cylinder 27L is expanded and the left expansion and contraction screed 31L is extruded. The same applies to a case where the right expansion and contraction screed 31R is retracted by the right screed expansion and contraction control valve 37R.

[0099] The pilot check valve 37P is configured to prevent the screed expansion and contraction cylinder 27 from unintentionally moving due to an external force. The pilot check valve 37P includes pilot check valves 37PaL, 37PaR, 37PbL, and 37PbR.

[0100] For example, in the pilot check valve 37PaL, only in a case where the left screed expansion and contraction control valve 37L operates in response to an operation of an operator and the hydraulic oil discharged by the cylinder pump 14M flows into the head-side oil chamber of the left screed expansion and contraction cylinder 27L, the hydraulic oil in the rod-side oil chamber of the left screed expansion and contraction cylinder 27L is allowed to flow toward the hydraulic oil tank T. In other cases, the pilot check valve 37PaL prohibits the hydraulic oil in the rod-side oil chamber of the left screed expansion and contraction cylinder 27L from flowing toward the hydraulic oil tank T. The same applies to the pilot check valves 37PbL, 37PaR, and 37PbR.

[0101] The relief valve 37V is configured to prevent a member related to the expansion and contraction screed 31 from being destroyed by an excessive external force acting in a direction where the expansion and contraction screed 31 is retracted. The relief valve 37V includes a left relief valve 37VL and a right relief valve 37VR.

[0102] For example, in a case where the pressure of hydraulic oil in the head-side oil chamber of the left screed expansion and contraction cylinder 27L is excessively increased by receiving excessive external force acting in the direction where the left screed expansion and contraction cylinder 27L is contracted, the left relief valve 37VL allows the hydraulic oil in the head-side oil chamber to flow out to the hydraulic oil tank T. As a result, the left screed expansion and contraction cylinder 27L contracts and absorbs a part of the external force to prevent the left expansion and contraction screed 31L from being damaged. The same applies to the right relief valve 37VR.[Specific Example of Method of Adjusting Driving Force of Front Wheel]

[0103] Next, in addition to Figs. 1A and 1B to 3, a method of adjusting the driving force of the front wheel 6 by the controller 50 will be specifically described with reference to Figs. 4 and 5A to 5D.

[0104] Fig. 4 is a graph illustrating an example of a method of controlling the driving force of the front wheel 6. Specifically, Fig. 4 includes a control rule 400 illustrating a relationship between the weight of the paving material inside the hopper 2 and the relief pressure (set value) of the relief valve RV set by the controller 50. Figs. 5A to 5D are front views illustrating a state of a paving material PM inside the hopper 2. Specifically, Fig. 5A illustrates a state of the paving material PM inside the hopper 2 immediately after the paving material PM is supplied by the dump truck. Fig. 5B illustrates a state of the paving material PM inside the hopper 2 when the amount decreases with respect to the state of Fig. 5A. Fig. 5C illustrates a state of the paving material PM inside the hopper 2 when the hopper 2 is closed to some extent (specifically, approximately half) due to a relative decrease in the amount of the paving material PM inside the hopper 2. Fig. 5D illustrates the amount of the paving material PM inside the hopper 2 when the amount of the paving material PM inside the hopper 2 is further reduced from the state of Fig. 5C and the hopper 2 is completely closed.

[0105] In Figs. 5A to 5D, the paving material PM in the hopper 2 is hatched with a satin finish. In addition, although the base portion 1BF of the tractor 1, the front wheel 6 (the left front wheel 6L and the right front wheel 6R), and the hopper cylinder 24 (the left hopper cylinder 24L and the right hopper cylinder 24R) are illustrated in Fig. 5A, these components are omitted in Figs. 5B to 5D. In addition, in Figs. 5A, 5C, and 5D, portions that are buried in the paving material PM and cannot be seen directly from the front (that is, are not exposed) are represented by dashed lines, of the inlet OPs of the conveyance passage CP provided in the front surface 1FW of the tractor 1.

[0106] As illustrated in Figs. 5A to 5D, the paving material PM is accommodated inside the hopper 2, specifically in a space surrounded by the front surface 1FW of the tractor 1 and the left and right hopper wings 2W (left hopper wing 2WL and right hopper wing 2WR).

[0107] As illustrated in Fig. 5A, a sufficient amount of the paving material PM is accumulated inside the hopper 2 immediately after the paving material PM is supplied from the dump truck. On the other hand, as illustrated in Figs. 5B to 5D, as the construction of the asphalt pavement by the asphalt finisher 100 progresses, the amount of the paving material PM inside the hopper 2 decreases. In this case, as illustrated in Fig. 5B, the amount decreases from the paving material PM in the central portion inside the hopper 2 where the conveyor CV is provided. Therefore, as illustrated in Figs. 5C and 5D, when the amount of the paving material inside the hopper 2 decreases to some extent, the hopper 2 is closed, and the paving materials PMs at both left and right end portions inside the hopper 2 are collected in the central portion. As a result, it is possible to suppress a situation where the paving material PM remains at the left and right end portions inside the hopper 2.

[0108] As described above, the hopper 2 may be closed by the operation of an operator who monitors the internal state of the hopper 2. In addition, the hopper 2 may be automatically closed regardless of the operation of the operator. In this case, the controller 50 may determine whether or not the closing operation of the hopper 2 is necessary according to the amount (estimated value) of the paving material inside the hopper 2 estimated based on the output of the space recognition device CM. In addition, the controller 50 may determine the closing amount (angle) of the hopper 2 based on the amount (estimated value) of the paving material. The controller 50 may control the hopper drive unit F6 (hopper control valve 34) such that the expansion and contraction amount of the hopper cylinder 24 becomes the determined closing amount of the hopper 2.

[0109] Here, in a state where the driving force of the front wheel 6 is maintained in a relatively high state, when the construction work of the asphalt pavement by the asphalt finisher 100 proceeds to some extent, the driving force of the front wheel 6 can be greater than the maximum frictional force between the front wheel 6 and the roadbed. This is because the load on the front wheel 6 decreases as the amount of the paving material PM inside the hopper 2 decreases in accordance with the progress of the construction work. Therefore, there is a possibility that the front wheel 6 may slip (wheel spin) to damage the roadbed, or the propulsive force of the asphalt finisher 100 is reduced.

[0110] On the other hand, in the present embodiment, the controller 50 (front wheel driving force control unit 50B) adjusts the driving force of the front wheel 6 according to the amount of the paving material inside the hopper 2. Specifically, the front wheel driving force control unit 50B adjusts the driving force of the front wheel 6 so that the driving force of the front wheel 6 decreases as the amount of the paving material inside the hopper 2 decreases. As a result, the controller 50 can suppress a situation where the driving force of the front wheel 6 becomes more excessive than the maximum frictional force of the front wheel 6 in a case where the weight of the paving material inside the hopper 2 is relatively reduced. Therefore, in the present embodiment, the controller 50 can suppress damage to the roadbed and a decrease in the propulsive force of the asphalt finisher 100 due to the slip of the front wheel 6.

[0111] For example, as illustrated in Fig. 4, the controller 50 may control the relief pressure (set value) of the relief valve RV in accordance with the control rule 400 such that the smaller the weight of the paving material inside the hopper 2, the smaller the relief pressure of the relief valve RV. As a result, the pressure (maximum value) of the hydraulic oil supplied to the front wheel traveling motor 22 through the oil passage between the front wheel traveling pump 14F and the front wheel traveling motor 22 decreases as the weight of the paving material inside the hopper 2 decreases. Therefore, the controller 50 can specifically reduce the driving force of the front wheel 6 according to the decrease in the amount of the paving material inside the hopper 2.

[0112] In addition, as described above, the controller 50 may adjust the driving force of the front wheel 6 by controlling the tilt angle of the swash plate of the front wheel traveling pump 14F in addition to controlling the relief pressure of the relief valve RV.

[0113] In addition, as described above, the controller 50 may specifically set a target value of the driving force of the front wheel 6 according to the weight of the paving material inside the hopper 2, and adjust the controlled variable of the relief valve RV and the front wheel traveling pump 14F (regulator) so as to achieve the target value. In this case, a control rule representing a relationship between the driving force (target value) of the front wheel 6 and a controlled variable (relief pressure or tilt angle) may be defined in advance.[Action]

[0114] Next, the actions of the asphalt finisher 100 according to the present embodiment will be described.

[0115] In the present embodiment, the asphalt finisher 100 is provided with the controller 50 (front wheel driving force control unit 50B) that controls the driving force of the front wheel 6 of the tractor 1 based on the weight of the paving material in the hopper 2. Specifically, the front wheel driving force control unit 50B changes the driving force of the front wheel 6 of the tractor 1 according to a change in the weight of the paving material inside the hopper 2.

[0116] As a result, the asphalt finisher 100 (controller 50) can adjust the driving force of the front wheel 6 according to a decrease in the amount of the paving material inside the hopper 2 as the construction work of the asphalt pavement progresses. Therefore, the asphalt finisher 100 can appropriately reduce the driving force of the front wheel 6 to suppress the slip of the front wheel 6 according to a decrease in the load on the front wheel 6 due to a decrease in the amount of the paving material inside the hopper 2. Therefore, the asphalt finisher 100 can suppress damage to the roadbed due to slip of the front wheel 6.

[0117] In addition, in the present embodiment, the front wheel driving force control unit 50B may reduce the driving force of the front wheel 6 when the weight of the paving material inside the hopper 2 decreases.

[0118] As a result, the asphalt finisher 100 (controller 50) can reduce the driving force of the front wheel 6 according to a decrease in the weight of the paving material inside the hopper 2, that is, a decrease in the load on the front wheel 6, and specifically suppress the slip of the front wheel 6.

[0119] In addition, in the present embodiment, the front wheel driving force control unit 50B may control the driving force of the front wheel 6 so as to maintain a target value changed according to a change in the weight of the paving material inside the hopper 2 while the tractor 1 travels.

[0120] As a result, the asphalt finisher 100 (controller 50) can appropriately adjust the driving force of the front wheel 6 according to a change in the weight of the paving material inside the hopper 2.

[0121] In addition, in the present embodiment, the front wheel driving force control unit 50B may control the driving force of the front wheel 6 by adjusting the relief pressure of the relief valve RV. In addition, in the present embodiment, the front wheel driving force control unit 50B may control the driving force of the front wheel 6 by adjusting the angle (tilt angle) of the swash plate of the front wheel traveling pump 14F.

[0122] As a result, the asphalt finisher 100 (controller 50) can specifically adjust the driving force of the front wheel 6 by controlling a controlled variable such as the relief pressure of the relief valve RV and the tilt angle of the swash plate of the front wheel traveling pump 14F.Reference Signs List

[0123] 1Tractor 2Hopper 2WHopper wing 2WLLeft hopper wing 2WRRight hopper wing 3Screed 3ALeveling arm 5Rear wheel 6Front wheel 14Hydraulic source 14CCharge pump 14EEngine 14FFront wheel traveling pump (hydraulic pump) 14MCylinder pump 14RRear wheel traveling pump 14SConveyor / screw pump 20LLeft rear wheel traveling motor 20LaCheck valve 20LbRelief valve 20RRight rear wheel traveling motor 20RaCheck valve 20RbRelief valve 21Conveyor / screw motor 21CLLeft conveyor motor 21CRRight conveyor motor 21SLLeft screw motor 21SRRight screw motor 22Front wheel traveling motor (hydraulic motor) 23Leveling cylinder 23LLeft leveling cylinder 23RRight leveling cylinder 24Hopper cylinder 24LLeft hopper cylinder 24RRight hopper cylinder 25Screed lift cylinder 25LLeft screed lift cylinder 25RRight screed lift cylinder 27Screed expansion and contraction cylinder 27LLeft screed expansion and contraction cylinder 27RRight screed expansion and contraction cylinder 30Main screed 31Expansion and contraction screed 33Leveling control valve 33LLeft leveling control valve 33RRight leveling control valve 33P, 33PaL, 33PaR, 33PbL, 33PbRPilot check valve 34Hopper control valve 34LLeft hopper control valve 34RRight hopper control valve 34P, 34PL, 34PRPilot check valve 35Screed lift control valve 35aSwitching valve 35bRelief valve 35cSwitching valve 37Screed expansion and contraction control valve 37P, 37PaL, 37PaR, 37PbL, 37PbRPilot check valve 37VRelief valve 37VLLeft relief valve 37VRRight relief valve 40Side plate 41Expansion and contraction moldboard 42Screed step 43Retaining plate 50Controller 50APaving material weight acquisition unit 50BFront wheel driving force control unit (control unit) 100Asphalt finisher CMSpace recognition device CPConveyance passage CVConveyor F1Rear wheel drive unit F2Conveyor / screw drive unit F3Front wheel drive unit F4Steering / compacting device drive unit F5Leveling unit F6Hopper drive unit F7Screed lift unit F8Screed expansion and contraction unit OCOil cooler OPInlet RVRelief valve SCScrew SCLELeft extension screw SCLMLeft main screw SCRERight extension screw SCRMRight main screw V0Speed reducer switching valve V1CConveyor control valve V1CLLeft conveyor control valve V1CRRight conveyor control valve V1SScrew control valve V1SLLeft screw control valve V1SRRight screw control valve V2Front wheel traveling valve

Claims

1. An asphalt finisher (100) comprising: a tractor (1); a hopper (2) installed on a front side of the tractor (1), and that receives a paving material; a conveyor (CV) that conveys the paving material in the hopper (2) to a rear side of the tractor (1); a screw (SC) that spreads out the paving material conveyed by the conveyor (CV) on the rear side of the tractor (1); a screed (3) that spreads and levels the paving material spread out by the screw (SC) on a rear side of the screw (SC); and a control unit (50B) that controls a driving force of a front wheel (6) of the tractor (1) based on a weight of the paving material in the hopper (2), characterized in that the asphalt finisher (100) further comprises: a retaining plate (43) that is a plate-shaped member for preventing the paving material, which is fed out in a vehicle width direction by the screw (SC), from being scattered in front of the screw (SC); a paving material weight acquisition unit configured to estimate the weight of the paving material inside the hopper; and a space recognition device (CM) configured to acquire data for monitoring a state of the paving material in the hopper (2), wherein the control unit (50B) is configured to control the driving force of the front wheel (6) based on an estimation result of the weight provided by the estimation unit, wherein the paving material weight acquisition unit is configured to estimate the weight based on an output of the space recognition device (CM), and a volume of the paving material in the hopper (2) is estimated in consideration of an open / closed state of the hopper (2) based on the output of the space recognition device (CM), and the weight is estimated based on the estimated volume.

2. The asphalt finisher (100) according to claim 1, wherein the control unit (50B) is configured to change the driving force of the front wheel (6) of the tractor (1) according to a change in the weight.

3. The asphalt finisher (100) according to claim 2, wherein the control unit (50B) is configured to control the driving force of the front wheel (6) so as to maintain a target value changed according to the change in the weight while the tractor (1) travels.

4. The asphalt finisher (100) according to claim 2 or 3, wherein the control unit (50B) is configured to reduce the driving force of the front wheel (6) when the weight is reduced.

5. The asphalt finisher (100) according to any one of claims 1 to 4, further comprising: a hydraulic motor (22) that drives the front wheel (6); a hydraulic pump (14F) that supplies hydraulic oil to the hydraulic motor (22); and a relief valve (RV) provided in an oil passage between the hydraulic pump (14F) and the hydraulic motor (22), wherein the control unit (50B) is configured to control the driving force of the front wheel (6) by adjusting a relief pressure of the relief valve (RV).

6. The asphalt finisher (100) according to claim 5, wherein the control unit (50B) is configured to control the driving force of the front wheel (6) by adjusting an angle of a swash plate of the hydraulic pump (14F).

7. The asphalt finisher (100) according to claim 5 or 6, wherein the control unit (50B) is configured to adjust the relief pressure of the relief valve (RV) in accordance with a control rule (400) that is defined such that the smaller the weight, the smaller the relief pressure, and represents a relationship between the weight and the relief pressure.

8. The asphalt finisher (100) according to claim 5 or 6, wherein the control unit (50B) is configured to set a target value of the driving force of the front wheel (6) in accordance with a control rule (400) that is defined such that the smaller the weight, the smaller the target value of the driving force of the front wheel (6), and represents a relationship between the weight and the target value of the driving force of the front wheel (6), and is configured to adjust the relief pressure of the relief valve (RV) so as to realize the target value of the driving force of the front wheel (6) in accordance with a control rule (400) that represents a relationship between the target value of the driving force of the front wheel (6) and the relief pressure.