Work vehicle, system including work vehicle, and method for controlling work vehicle

Abstract

According to the present invention, a driver's seat (5S) is disposed on a floor (5F). A seat suspension (40) has a variable damper element (20) that is disposed between the floor (5F) and the driver's seat (5S), and that is capable of switching a damping force between at least a first damping force and a second damping force that is greater than the first damping force. A displacement sensor (41) detects a relative displacement amount of the driver's seat (5S) with respect to the floor (5F). A controller (50) switches the damping force of the variable damper element (20) from the first damping force to the second damping force in a case in which a peak value of the relative displacement amount detected by the displacement sensor (41) is greater than a first predetermined value (PL1).

Description

Work vehicle, system including work vehicle, and work vehicle control method

[0001] The present disclosure relates to a work vehicle, a system including a work vehicle, and a method for controlling a work vehicle.

[0002] In work vehicles such as hydraulic excavators and wheel loaders, the driver's seat was fixed to the floor of the cab, so-called rigid seats were used. However, to improve ride comfort and reduce operator fatigue, work vehicles with mechanical suspension or air suspension between the driver's seat and the floor have appeared.

[0003] There are also work vehicles that allow the hardness of the dampers included in the seat suspension to be adjusted in multiple stages to suit the operator's preferences. Work vehicles that allow the hardness of the dampers to be adjusted are disclosed in Japanese Patent Laid-Open No. 2000-85435 (Patent Document 1), Japanese Patent Laid-Open No. 2000-85436 (Patent Document 2), etc.

[0004] JP 2000-85435 A JP 2000-85436 A

[0005] Work vehicles often travel through work sites with poor footing and often have to overcome bumps while traveling. Therefore, there is a demand for improved ride comfort even in such situations.

[0006] An object of the present disclosure is to provide a work vehicle, a system including a work vehicle, and a control method for a work vehicle that can improve ride comfort while traveling.

[0007] Each of the work vehicles and systems including the work vehicle of the present disclosure includes a work machine, a floor, a driver's seat, a seat suspension, a displacement sensor, and a controller. The driver's seat is disposed on the floor. The seat suspension is disposed between the floor and the driver's seat and has a variable damper element capable of switching damping force between at least a first damping force and a second damping force greater than the first damping force. The displacement sensor detects the amount of relative displacement of the driver's seat with respect to the floor. The controller switches the damping force of the variable damper element from the first damping force to the second damping force when the peak value of the amount of relative displacement detected by the displacement sensor is greater than a first predetermined value.

[0008] The control method for a work vehicle disclosed herein is a control method for a work vehicle having a work machine, a floor, a driver's seat arranged on the floor, a seat suspension arranged between the floor and the driver's seat and having a variable damper element capable of switching damping force between at least a first damping force and a second damping force greater than the first damping force, and a displacement sensor that detects the amount of relative displacement of the driver's seat with respect to the floor, and has the following steps:

[0009] A relative displacement of the driver's seat with respect to the floor is acquired. It is determined whether a peak value of the relative displacement detected by the displacement sensor is greater than a first predetermined value. If it is determined that the peak value is greater than the first predetermined value, the damping force of the variable damper element is switched from a first damping force to a second damping force.

[0010] According to the present disclosure, it is possible to realize a work vehicle, a system including a work vehicle, and a method for controlling a work vehicle that can improve ride comfort while traveling.

[0011] FIG. 1 is a side view showing the configuration of a wheel loader (an example of a work vehicle) according to an embodiment of the present disclosure. FIG. 2 is a diagram showing the configuration of a system including a work vehicle according to an embodiment of the present disclosure. FIG. 3 is a cross-sectional view showing the configuration of a variable damper element employed in a system including a work vehicle according to an embodiment of the present disclosure. FIG. 4 is a diagram showing functional blocks of a controller employed in a system including a work vehicle according to an embodiment of the present disclosure. FIG. 5 is a diagram showing (A) how a work vehicle travels, (B) a diagram showing the time change in the amount of relative displacement between the floor of the cab and the driver's seat during travel, (C) a diagram showing the time change in acceleration of the floor (base) in the cab, and (D) a diagram showing the time change in a command current value given to a variable damper element. FIG. 6 is a first flowchart showing a method for controlling a work vehicle according to an embodiment of the present disclosure. FIG. 7 is a second flowchart showing a method for controlling a work vehicle according to an embodiment of the present disclosure. FIG. 8 is a third flowchart showing a method for controlling a work vehicle according to an embodiment of the present disclosure.

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the specification and drawings, identical or corresponding components are designated by the same reference numerals, and redundant explanations will not be repeated. In addition, in the drawings, configurations may be omitted or simplified for the sake of convenience.

[0013] In the following description, the terms "up," "down," "front," "rear," "left," and "right" refer to directions relative to an operator seated in the driver's seat 5S in the driver's cab 5 shown in Fig. 1. In Fig. 1, the front-to-rear direction is indicated by Z, with Zf indicating the front direction and Zb indicating the rear direction. In Fig. 2, the up-down direction is indicated by Y.

[0014] <Configuration of Work Vehicle> The configuration of a wheel loader will be described as an example of a work vehicle in this embodiment using Figure 1. Note that the work vehicle in this embodiment is not limited to a wheel loader. The work vehicle in this embodiment may be any work vehicle that has a work implement and a driver's seat, and may also be a hydraulic excavator, bulldozer, motor grader, etc.

[0015] Figure 1 is a side view showing the configuration of a wheel loader according to one embodiment of the present disclosure. As shown in Figure 1, the wheel loader 1 according to this embodiment has a running body 2 and a work implement 3. The work implement 3 is disposed on the running body 2. The running body 2 has a body frame 10, a pair of front wheels 4, a driver's compartment (cab) 5, an engine compartment 6, a pair of rear wheels 7, and a steering cylinder 9. The wheel loader 1 uses the work implement 3 to perform work such as loading earth and sand.

[0016] The body frame 10 is of a so-called articulated (rotating) type and includes a front frame 11, a rear frame 12, and a connecting shaft 13. The front frame 11 is disposed in a forward direction Zf of the rear frame 12. The connecting shaft 13 is provided in the center of the body frame 10 in the left-right direction (vehicle width direction), and connects the front frame 11 and the rear frame 12 to each other so that they can rotate. A pair of front wheels 4 are attached to the left and right of the front frame 11. Furthermore, a pair of rear wheels 7 are attached to the left and right of the rear frame 12.

[0017] The work implement 3 is driven by hydraulic oil from a work implement pump (not shown). The work implement 3 has a boom 14, a bucket 15, a lift cylinder 16, a bucket cylinder 17, and a bell crank 18. The boom 14 is attached to the front frame 11. The bucket 15 is attached to the tip of the boom 14.

[0018] The lift cylinder 16 and the bucket cylinder 17 are hydraulic cylinders. One end of the lift cylinder 16 is attached to the front frame 11, and the other end of the lift cylinder 16 is attached to the boom 14. The boom 14 rotates up and down as the lift cylinder 16 extends and retracts. One end of the bucket cylinder 17 is attached to the front frame 11, and the other end of the bucket cylinder 17 is attached to the bucket 15 via a bell crank 18. The bucket 15 rotates up and down as the bucket cylinder 17 extends and retracts.

[0019] The operator's cab 5 is mounted on the rear frame 12. Inside the operator's cab 5, there are arranged an operator's seat 5S for an operator to sit in, a handle for steering, levers for operating the work implement 3, various switches, display devices, etc. The engine room 6 is arranged on the rear frame 12 in the rear direction Zb of the operator's cab 5 and houses an engine.

[0020] <Configuration of a System Including a Work Vehicle> Next, the configuration of a system including a work vehicle in this embodiment will be described with reference to FIGS. 2 to 4. FIG.

[0021] Fig. 2 is a diagram showing the configuration of a system including a work vehicle according to an embodiment of the present disclosure. Fig. 3 is a cross-sectional view showing the configuration of a variable damper element employed in a system including a work vehicle according to an embodiment of the present disclosure. Fig. 4 is a diagram showing functional blocks of a controller employed in a system including a work vehicle according to an embodiment of the present disclosure.

[0022] As shown in FIG. 2, the system including the work vehicle has a seat suspension 40 , a displacement sensor 41 , a current regulator 42 , an acceleration sensor 43 , and a controller 50 .

[0023] The driver's cab 5 has a floor 5F. A driver's seat 5S is disposed on the floor 5F of the driver's cab 5. A seat suspension 40 is disposed between the floor 5F and the driver's seat 5S.

[0024] The seat suspension 40 has a variable damper element 20 and an elastic member 30. The variable damper element 20 absorbs vibrations in the up-down direction Y of the driver's seat 5S. The variable damper element 20 is configured to be able to change the damping force of the vibrations in the up-down direction Y of the driver's seat 5S. The variable damper element 20 is able to switch the damping force between at least a first damping force and a second damping force that is greater than the first damping force. One end (e.g., the lower end) of the variable damper element 20 is fixed to the floor 5F, and the other end (e.g., the upper end) is fixed to the driver's seat 5S.

[0025] The elastic member 30 absorbs vibrations in the vertical direction Y of the driver's seat 5S that cannot be fully absorbed by the variable damper element 20. The elastic member 30 is made of, for example, a spring. One end (for example, the lower end) of the elastic member 30 is fixed to the floor 5F, and the other end (for example, the upper end) is fixed to the driver's seat 5S.

[0026] One end of each of the variable damper element 20 and the elastic member 30 may be fixed directly to the floor 5F, or may be fixed indirectly via a bracket or the like. The other end of each of the variable damper element 20 and the elastic member 30 may be fixed directly to the driver's seat 5S, or may be fixed indirectly via a bracket or the like.

[0027] The displacement sensor 41 detects the amount of displacement of the driver's seat 5S relative to the floor 5F. The displacement sensor 41 is fixed to, for example, the floor 5F. The displacement sensor 41 may be fixed directly to the floor 5F, or may be fixed indirectly via a bracket or the like. The displacement sensor 41 may also be fixed to, for example, the driver's seat 5S. In this case, the displacement sensor 41 may be fixed directly to the driver's seat 5S, or may be fixed indirectly via a bracket or the like.

[0028] The current adjusting device 42 is electrically connected to the coil 25 (FIG. 3) of the variable damper element 20. The current adjusting device 42 adjusts the amount of current supplied to the coil 25 of the variable damper element 20. The current adjusting device 42 can, for example, switch between a state in which current is supplied to the coil 25 of the variable damper element 20 and a state in which the current supply is cut off.

[0029] The acceleration sensor 43 detects the acceleration of the floor 5F. The acceleration sensor 43 is fixed to the floor 5F, for example. The acceleration sensor 43 may be fixed directly to the floor 5F, or may be fixed indirectly via a bracket or the like.

[0030] The controller 50 includes a processor, a main memory, and a storage. The processor is, for example, a CPU (Central Processing Unit). The main memory includes, for example, a non-volatile memory such as a ROM (Read Only Memory) and a volatile memory such as a RAM (Random Access Memory). The controller 50 reads a program stored in the storage, loads it into the main memory, and executes predetermined processing in accordance with the program.

[0031] The controller 50 is electrically connected to each of the displacement sensor 41, the current adjuster 42, and the acceleration sensor 43. The controller 50 acquires displacement data detected by the displacement sensor 41. The controller 50 controls the current adjuster 42 based on the displacement data detected by the displacement sensor 41. The controller 50 acquires acceleration data detected by the acceleration sensor 43. The controller 50 controls the current adjuster 42 based on the acceleration data detected by the acceleration sensor 43. The controller 50 adjusts the amount of current supplied to the coil 25 of the variable damper element 20 by controlling the current adjuster 42. In this way, the controller 50 adjusts the damping force of the variable damper element 20 between at least a first damping force and a second damping force.

[0032] The first damping force is, for example, the damping force of the variable damper element 20 when the current supply to the coil 25 of the variable damper element 20 is cut off. The second damping force is, for example, the damping force of the variable damper element 20 when the current is supplied to the coil 25 of the variable damper element 20.

[0033] However, the first damping force only needs to be smaller than the second damping force, and may be the damping force in a state where a current is supplied to the coil 25 of the variable damper element 20. In this case, the first damping force is the damping force in a state where a current amount smaller than the current amount that is passed through the coil 25 of the variable damper element 20 to obtain the second damping force is supplied.

[0034] The floor 5F may be any base supported by the traveling body 2, and may be any member that supports the driver's seat 5S via the seat suspension 40.

[0035] The controller 50 may be mounted on the wheel loader 1, or may be located remotely outside the wheel loader 1. When the controller 50 is located remotely outside the wheel loader 1, the controller 50 may be connected wirelessly to the displacement sensor 41, the current adjuster 42, the acceleration sensor 43, etc. The controller 50 may be stored in a server located remotely from the wheel loader 1.

[0036] As shown in FIG. 3, the variable damper element 20 includes a cylinder 21, a piston 22, a piston rod 23, a diaphragm 24, a coil 25, wiring 26, a magnetorheological fluid 27, and a seal bearing 28.

[0037] The cylinder 21 has a cylindrical shape (for example, a cylindrical shape). A piston 22 and a diaphragm 24 are disposed in the cylindrical internal space of the cylinder 21. The piston 22 is slidable along the axial direction AX of the cylinder 21 while contacting the inner circumferential surface of the cylinder 21.

[0038] The piston rod 23 has a first end and a second end that face each other in the axial direction AX. The first end of the piston rod 23 is connected to the piston 22 and is located in the interior space of the cylinder 21. The second end of the piston rod 23 is located outside the cylinder 21. The piston rod 23 is supported by a seal bearing 28 so as to be movable in the axial direction AX relative to the cylinder 21.

[0039] The internal space of the cylinder 21 is divided into a first fluid chamber 21A and a second fluid chamber 21B by the piston 22. The piston 22 has an annular orifice 22a that connects the first fluid chamber 21A and the second fluid chamber 21B. The annular orifice 22a penetrates the piston 22 in the axial direction AX.

[0040] The magnetorheological fluid 27 fills the first fluid chamber 21A, the second fluid chamber 21B, and the annular orifice 22a. The viscosity of the magnetorheological fluid 27 changes depending on the strength of the magnetic field acting on the magnetorheological fluid 27. For example, when no magnetic field is applied, the magnetorheological fluid 27 is in a low-viscosity liquid state, but when a magnetic field is applied, the viscosity increases and the fluid behaves like a semi-solid. The magnetorheological fluid 27 is a liquid such as oil or water in which ferromagnetic particles with a diameter of 1 μm to 10 μm are uniformly dispersed.

[0041] The diaphragm 24 divides the internal space of the cylinder 21 into a second fluid chamber 21B and a gas chamber 21C. The gas chamber 21C functions as an accumulator. A free piston may be used instead of the diaphragm.

[0042] The coil 25 is provided inside the piston 22. When energized, the coil 25 generates a magnetic field, which acts on the magnetorheological fluid 27. A wire 26 is electrically connected to the coil 25. The coil 25 is electrically connected to a current adjusting device 42 through the wire 26. This allows the current adjusting device 42 to adjust the amount of current supplied to the coil 25 through the wire 26.

[0043] 4, the controller 50 includes a displacement information acquisition unit 51, a displacement information determination unit 52, a damping force control unit 53, an acceleration information acquisition unit 54, an acceleration information determination unit 55, and a memory 56. The displacement information acquisition unit 51 acquires a signal indicating the amount of relative displacement of the driver's seat 5S in the up-down direction Y with respect to the floor 5F detected by the displacement sensor 41.

[0044] The displacement information determination unit 52 obtains the peak value of the relative displacement obtained by the displacement information acquisition unit 51. The displacement information determination unit 52 determines whether the peak value of the obtained relative displacement is greater than a first predetermined value PL1 ( FIG. 5B ). When making this determination, the displacement information determination unit 52 refers to the first predetermined value PL1 stored in the memory 56. The damping force control unit 53 outputs a command current that controls the current adjustment device 42 based on the determination result obtained by the displacement information determination unit 52.

[0045] When the damping force control unit 53 obtains from the displacement information determination unit 52 a determination result that the peak value of the relative displacement amount is greater than the first predetermined value PL1, the damping force control unit 53 outputs a command current to the current adjustment device 42 to switch the damping force of the variable damper element 20 from the first damping force to the second damping force. In this way, when the controller 50 determines that the peak value of the relative displacement amount is greater than the first predetermined value PL1, the controller 50 switches the damping force of the variable damper element 20 from the first damping force to the second damping force.

[0046] Furthermore, when the damping force control unit 53 obtains from the displacement information determination unit 52 a determination result that the peak value of the relative displacement amount is equal to or less than the first predetermined value PL1, the damping force control unit 53 outputs a command current to the current adjustment device 42 to maintain the damping force of the variable damper element 20 at the current damping force. In this way, when the controller 50 determines that the peak value of the relative displacement amount is equal to or less than the first predetermined value PL1, the controller 50 maintains the damping force of the variable damper element 20 at the current damping force.

[0047] The displacement information determination unit 52 also determines whether the absolute value of the peak of the acquired relative displacement is less than a second predetermined value PL2 (FIG. 5B). The second predetermined value PL2 is a value smaller than the first predetermined value PL1. When making this determination, the displacement information determination unit 52 refers to the second predetermined value PL2 stored in the memory 56.

[0048] When the damping force control unit 53 obtains from the displacement information determination unit 52 a determination result that the peak absolute value of the relative displacement amount is less than the second predetermined value PL2, the damping force control unit 53 outputs a command current to the current adjustment device 42 to switch the damping force of the variable damper element 20 from the second damping force to the first damping force. In this way, when the controller 50 determines that the peak absolute value of the relative displacement amount is less than the second predetermined value PL2, the controller 50 switches the damping force of the variable damper element 20 from the second damping force to the first damping force.

[0049] The acceleration information acquisition unit 54 acquires a signal indicating the acceleration of the floor 5F in the vertical direction Y detected by the acceleration sensor 43. The acceleration information determination unit 55 determines whether the absolute value of a first peak in the acceleration waveform of the floor 5F acquired by the acceleration information acquisition unit 54 is greater than the absolute value of a second peak immediately before (just before) the first peak. For example, as shown in FIG. 5C , the acceleration information determination unit 55 determines whether the absolute value α1 of a first peak PB1 in the acceleration waveform of the floor 5F is greater than the absolute value α2 of a second peak PB2 immediately before the first peak PB1. At this time, the acceleration information determination unit 55 may refer to the acceleration waveform of the floor 5F stored in the memory 56. The memory 56 may store acceleration information (including acceleration peak values) acquired by the acceleration information determination unit 55.

[0050] The damping force control unit 53 outputs a command current for controlling the damping force of the variable damper element 20 to the current adjustment device 42 based on the determination result of the acceleration information determination unit 55. When the damping force control unit 53 obtains a determination result from the acceleration information determination unit 55 that the absolute value of the first peak is greater than the absolute value of the second peak, the damping force control unit 53 outputs a command current for switching the damping force of the variable damper element 20 from the second damping force to the first damping force to the current adjustment device 42. In this way, when the controller 50 determines that the absolute value of the first peak is greater than the absolute value of the second peak, the controller 50 switches the damping force of the variable damper element 20 from the second damping force to the first damping force.

[0051] The current adjusting device 42 adjusts the value of the current supplied to the coil 25 of the variable damper element 20 based on the command current obtained from the damping force control unit 53. When the current adjusting device 42 obtains from the damping force control unit 53 a command current for causing the variable damper element 20 to have a first damping force, the current adjusting device 42 does not supply current to the coil 25 of the variable damper element 20 (cuts off the current supply), for example. On the other hand, when the current adjusting device 42 obtains from the damping force control unit 53 a command current for causing the variable damper element 20 to have a second damping force, the current adjusting device 42 supplies current to the coil 25 of the variable damper element 20, for example. In this way, the current adjusting device 42 adjusts the damping force of the variable damper element 20 by on / off control that supplies or cuts off the current supply to the coil 25 of the variable damper element 20.

[0052] Furthermore, the current adjustment device 42 may adjust the damping force of the variable damper element 20 by a method other than the on / off control described above. The current adjustment device 42 may adjust the damping force of the variable damper element 20, for example, by changing (increasing or decreasing) the amount of current supplied to the coil 25 of the variable damper element 20. Specifically, the amount of current supplied to the coil 25 may be controlled to be small when adjusting the damping force of the variable damper element 20 to a first damping force, and to be large when adjusting the damping force of the variable damper element 20 to a second damping force.

[0053] <Method of Controlling a Work Vehicle> Next, a method of controlling a work vehicle in this embodiment will be described with reference to Figs. 5 to 8, using as an example a state in which the wheel loader 1 climbs over a step while traveling.

[0054] 5A shows a diagram illustrating the traveling state of a work vehicle, FIG. 5B shows a diagram illustrating the time change in the relative displacement between the floor of the cab and the driver's seat while traveling, FIG. 5C shows a diagram illustrating the time change in the acceleration of the floor (base) of the cab, and FIG. 5D shows the time change in the command current value given to the variable damper element. FIGS. 6 to 8 are flow charts illustrating a control method for a work vehicle according to an embodiment of the present disclosure.

[0055] As shown in Figure 5(A), while the wheel loader 1 is traveling forward, there are cases where the front wheels 4 of the wheel loader 1 run up a step ST, and then the rear wheels 7 run up the step ST. In this case, the amount of relative displacement in the up-down direction Y of the driver's seat 5S with respect to the floor 5F of the driver's cab 5 changes, for example, as shown in Figure 5(B).

[0056] The arrow AR1 shown in Figure 5(B) and the arrow AR3 in Figure 5(C) each indicate the point in time when the front wheels 4 of the wheel loader 1 run up onto the step ST. The arrow AR2 in Figure 5(B) and the arrow AR4 in Figure 5(C) each indicate the point in time when the rear wheels 7 of the wheel loader 1 run up onto the step ST.

[0057] The arrows ARA, ARC, and ARD shown in Fig. 5(D) indicate the time points at which the relative displacement reaches peaks PA1, PA2, and PA3, respectively, as shown in Fig. 5(B). The arrow ARB shown in Fig. 5(D) indicates the time point at which the acceleration of the floor 5F of the cab in the vertical direction Y reaches peak PB1, as shown in Fig. 5(C).

[0058] As shown in Figure 5 (B), when the front wheels 4 of the wheel loader 1 run over a step ST, the impact pushes up the floor 5F of the cab 5. As a result, the floor 5F approaches the driver's seat 5S via the seat suspension 40, and the driver's seat 5S is displaced relative to the floor 5F in the negative direction. After this, the restoring force of the elastic member 30 (Figure 2) causes the driver's seat 5S to move away from the floor 5F, and the driver's seat 5S is displaced relative to the floor 5F in the positive direction. After this, the amount of relative displacement of the driver's seat 5S with respect to the floor 5F gradually attenuates as displacement in the negative direction and displacement in the positive direction are repeated.

[0059] After this, when the rear wheels 7 of the wheel loader 1 run over the step ST, the impact pushes up the floor 5F of the cab 5 again. As a result, the floor 5F approaches the driver's seat 5S via the seat suspension 40, and the driver's seat 5S is displaced relative to the floor 5F in the negative direction. After this, the restoring force of the elastic member 30 (FIG. 2) moves the driver's seat 5S away from the floor 5F, and the driver's seat 5S is displaced relative to the floor 5F in the positive direction. After this, the amount of relative displacement of the driver's seat 5S with respect to the floor 5F gradually attenuates as displacement in the negative direction and displacement in the positive direction are repeated.

[0060] In this embodiment, the amount of relative displacement of the driver's seat 5S relative to the floor 5F in the up-down direction Y is detected by the displacement sensor 41. The displacement sensor 41 outputs a signal indicating the detected amount of relative displacement to the controller 50. The displacement information acquisition unit 51 of the controller 50 acquires the signal indicating the amount of relative displacement of the driver's seat 5S output from the displacement sensor 41 (step S1: FIG. 6). The amount of relative displacement has a waveform such as that shown in FIG. 5(B), for example. The displacement information acquisition unit 51 outputs the signal indicating the amount of relative displacement to the displacement information determination unit 52.

[0061] The displacement information determination unit 52 recognizes a peak in the waveform of the relative displacement amount, acquires the relative displacement amount (peak value) at the recognized peak (step S2: FIG. 6), and determines whether the peak value of the acquired relative displacement amount is greater than a first predetermined value PL1 (step S3: FIG. 6).

[0062] If the displacement information determiner 52 determines that the peak value of the relative displacement amount is greater than the first predetermined value PL1, the displacement information determiner 52 outputs a signal indicating the determination result to the damping force control unit 53. In this case, the damping force control unit 53 outputs a command current to the current adjuster 42 to switch the damping force of the variable damper element 20 from the first damping force to the second damping force (step S4: FIG. 6). Specifically, the damping force control unit 53 controls the current adjuster 42 to supply current to the coil 25 of the variable damper element 20, for example, as indicated by arrows ARA and ARC in FIG. 5(D).

[0063] At this time, as shown in Figure 5 (B), when the relative displacement amount becomes larger than the first predetermined value PL1 and the relative displacement amount changes from increasing to decreasing (the point indicated by arrows ARA and ARC), the controller 50 switches the damping force of the variable damper element 20 from the first damping force to the second damping force.

[0064] 5(D), the controller 50 controls the value of the command current provided to the variable damper element 20 so that it increases from a first current value C0 (for example, 0) to a second current value C1 that is greater than the first current value C0 while sloping along the time axis. In other words, the controller 50 increases the command current value from the first current value C0 to the second current value C1 over time T, thereby sloping the rise of the command current value from the first current value C0 to the second current value C1 along the time axis.

[0065] The time T during which the command current value is increased from the first current value C0 to the second current value C1 may be longer than the time from peak PA1 or PA2 to the next (immediately following) peak in the waveform of the relative displacement. Furthermore, it is preferable that this time T be constant for each rise of the command current value from the first current value C0 to the second current value C1. The time T may be changed as appropriate. It is also preferable that the rate of increase of the command current value from the first current value C0 to the second current value C1 be constant.

[0066] On the other hand, if the displacement information determination unit 52 determines in step S3 of FIG. 6 that the peak value of the relative displacement amount is less than the first predetermined value PL1, steps S1, S2, and S3 of FIG. 6 are repeated.

[0067] 6, the acceleration of the floor 5F is also acquired and determined. The variable damper element 20, which has been set to the second damping force in the above control, is switched from the second damping force to the first damping force as follows, based on the determination result of the acceleration of the floor 5F.

[0068] The acceleration (base acceleration) of the floor 5F is detected by the acceleration sensor 43. The acceleration sensor 43 outputs a signal indicating the detected acceleration to the controller 50. The acceleration information acquisition unit 54 of the controller 50 acquires the signal indicating the acceleration of the floor 5F output from the acceleration sensor 43 (step S11: FIG. 7). The acceleration of the floor 5F has a waveform such as that shown in FIG. 5(C), for example. The acceleration information acquisition unit 54 outputs the signal indicating the acceleration to the acceleration information determination unit 55.

[0069] The acceleration information determination unit 55 recognizes a peak (acceleration peak) in the acceleration waveform. The acceleration information determination unit 55 obtains the absolute value of the acceleration at the recognized acceleration peak (step S12: FIG. 7). The acceleration information determination unit 55 determines whether the absolute value of the obtained acceleration peak (first peak) is greater than the absolute value of the immediately preceding (previous) acceleration peak (second peak) (step S13: FIG. 7).

[0070] If the acceleration information determiner 55 determines that the absolute value of the acceleration peak is greater than the absolute value of the immediately preceding acceleration peak, the acceleration information determiner 55 outputs a signal indicating the determination result to the damping force control unit 53. In this case, the damping force control unit 53 outputs a command current value to the current adjuster 42 to switch the damping force of the variable damper element 20 from the second damping force to the first damping force (step S14: FIG. 7). If the damping force control unit 53 obtains a determination result that the absolute value of the acceleration peak is greater than the absolute value of the immediately preceding acceleration peak, the damping force control unit 53 controls the current adjuster 42 to, for example, cut off the current supply to the coil 25 of the variable damper element 20, as indicated by arrow ARB in FIG. 5(D). Note that the determination for switching the damping force of the variable damper element 20 from the second damping force to the first damping force at the timing indicated by arrow ARB may be a determination other than whether the absolute value of the acceleration peak is greater than the absolute value of the immediately preceding acceleration peak. The acceleration information determination unit 55 may, for example, perform control to switch the damping force of the variable damper element 20 from the second damping force to the first damping force based on the determination result that the effective value of the relative displacement is equal to or greater than a predetermined value. Furthermore, the determination to switch the damping force of the variable damper element 20 from the second damping force to the first damping force at the timing indicated by the arrow ARB may be a combination of determining whether the absolute value of the acceleration peak is greater than the absolute value of the immediately preceding acceleration peak and determining that the effective value of the relative displacement is equal to or greater than a predetermined value.

[0071] As a result of the above, for example, when the absolute value α1 of the acceleration peak PB1 (first peak) is greater than the absolute value α2 of the immediately preceding acceleration peak PB2 (second peak) as shown in FIG. 5(C), the current supply to the coil 25 of the variable damper element 20 is cut off as shown in FIG. 5(D).

[0072] On the other hand, if the acceleration information determination unit 55 determines in step S13 of FIG. 7 that the absolute value of the acceleration peak is equal to or less than the absolute value of the immediately preceding acceleration peak, steps S11, S12, and S13 of FIG. 7 are repeated.

[0073] In addition, in the control shown in Figure 6, the variable damper element 20, which has been set to the second damping force, is switched from the second damping force to the first damping force as follows based on the determination result of the peak value of the relative displacement of the driver's seat 5S with respect to the floor 5F.

[0074] The displacement information acquisition unit 51 of the controller 50 acquires a signal indicating the relative displacement amount of the driver's seat 5S output from the displacement sensor 41 (step S21: FIG. 8 ). The displacement information acquisition unit 51 outputs the signal indicating the relative displacement amount to the displacement information determination unit 52.

[0075] The displacement information determination unit 52 acquires a peak (displacement peak) in the waveform of the relative displacement amount. The displacement information determination unit 52 acquires the absolute value of the relative displacement amount at the acquired displacement peak (step S22: FIG. 8). The displacement information determination unit 52 determines whether the absolute value of the acquired displacement peak is less than a second predetermined value PL2 (step S23: FIG. 8).

[0076] If the displacement information determiner 52 determines that the absolute value of the displacement peak is less than the second predetermined value PL2, the displacement information determiner 52 outputs a signal indicating the determination result to the damping force control unit 53. In this case, the damping force control unit 53 outputs a command current to the current adjuster 42 to switch the damping force of the variable damper element 20 from the second damping force to the first damping force (step S24: FIG. 6). Specifically, as shown by the arrow ARD in FIG. 5(D), the damping force control unit 53 controls the current adjuster 42 to, for example, cut off the current supply to the coil 25 of the variable damper element 20. Note that the determination for switching the damping force of the variable damper element 20 from the second damping force to the first damping force at the timing shown by the arrow ARD may be a determination other than whether the absolute value of the displacement peak is less than the second predetermined value PL2. The displacement information determination unit 52 may control the damping force of the variable damper element 20 to be switched from the second damping force to the first damping force based on the determination result that the effective value of the relative displacement for the past 0.2 seconds (approximately 1 / 2 wavelength of the suspension vibration) is less than a predetermined value, for example.

[0077] As a result of the above, when the absolute value of the peak value is less than the second predetermined value PL2, for example, as in the case of the displacement peak PA3 shown in Figure 5(B), the controller 50 controls the current adjusting device 42 to cut off the current supply to the coil 25 of the variable damper element 20, for example, as shown in Figure 5(D).

[0078] On the other hand, if the displacement information determination unit 52 determines in step S23 of FIG. 8 that the absolute value of the displacement peak is equal to or greater than the second predetermined value PL2, steps S21, S22, and S23 of FIG. 8 are repeated.

[0079] 6 to 8 , as shown in FIG. 5 , current is supplied to the coil 25 of the variable damper element 20, keeping it in the ON state, from time ARA when a displacement peak PA1 having a peak value greater than the first predetermined value PL1 is detected until time ARB when an acceleration peak PB1 having an absolute value α1 greater than the absolute value α2 of the immediately preceding acceleration peak PB2 is detected. Furthermore, current supply to the coil 25 of the variable damper element 20 is interrupted, keeping it in the OFF state, from time ARB to time ARC when a displacement peak PA2 having a peak value greater than the first predetermined value PL1 is detected. Furthermore, current is supplied to the coil 25 of the variable damper element 20, keeping it in the ON state, from time ARC to time ARD when a displacement peak PA3 having an absolute value less than the second predetermined value PL2 is detected. Furthermore, after time ARD has passed, current supply to the coil 25 of the variable damper element 20 is interrupted, keeping it in the OFF state.

[0080] Note that, in the above, a case where the rear wheels 7 run over a step ST is described as the second run over of a step ST, but the second run over of a step may also be when the front wheels 4 run over a second step. Similar control may also be executed for the third and subsequent run over of a step. For example, the order in which steps ST are run over is not limited to front wheels → rear wheels, but may be front wheels → front wheels → rear wheels → rear wheels. Furthermore, in the above, a case in which the wheel loader 1 is moving forward is described, but the same control as in the case of moving forward may also be executed when moving backward.

[0081] <Effects> Next, the effects of this embodiment will be described.

[0082] In this embodiment, as shown in FIG. 5B , when the peak value of the relative displacement detected by the displacement sensor 41 is greater than a first predetermined value PL1, the damping force of the variable damper element 20 is switched from the first damping force to the second damping force. As a result, until the peak value of the relative displacement becomes greater than the first predetermined value PL1, the damping force of the variable damper element 20 is set to the small first damping force, making it easier to absorb impacts. After the peak value of the relative displacement becomes greater than the first predetermined value PL1, the damping force of the variable damper element 20 is set to the large second damping force, making it possible to quickly absorb vibrations of the driver's seat 5S in the up-down direction Y relative to the floor 5F. This improves ride comfort when the wheel loader 1 goes over steps while traveling.

[0083] In this embodiment, as shown in FIG. 5C , the controller 50 switches the damping force of the variable damper element 20 from the second damping force to the first damping force when it determines that the absolute value α1 of the first peak PB1 in the waveform of the acceleration of the floor 5F detected by the acceleration sensor 43 is greater than the absolute value α2 of the second peak PB2 immediately preceding the first peak PB1. This makes it easier for the variable damper element 20 to mitigate the impact when the vehicle runs over a step ST for the second or subsequent times. Furthermore, by focusing on acceleration as described above, it becomes easier to identify the second or subsequent times the wheel runs over a step ST. In this way, focusing on the relative displacement makes it possible to identify the first runover of a step ST, and focusing on acceleration makes it easy to identify the second or subsequent runover of a step ST.

[0084] 5B, in this embodiment, when the amount of relative displacement detected by the displacement sensor 41 becomes larger than a first predetermined value PL1 and it is determined that the relative displacement has changed from increasing to decreasing, the controller 50 switches the damping force of the variable damper element 20 from the first damping force to the second damping force. This makes it possible to switch the damping force based on the peak of the amount of relative displacement.

[0085] 5B, in this embodiment, when the absolute value of the peak PA3 of the relative displacement is less than the second predetermined value PL2, the controller 50 sets the damping force of the variable damper element 20 to the small first damping force. This makes it possible to reduce the amount of current supplied to the variable damper element 20 when the vibration of the driver's seat 5S is weak.

[0086] If the command current value is instantaneously increased from the first current value to the second current value at the peak of the relative displacement, the convergence of the vibration of the driver's seat 5S relative to the floor 5F will be delayed. Therefore, in this embodiment, as shown in Figure 5(D), the controller 50 switches the damping force of the variable damper element 20 from the first damping force to the second damping force by increasing the value of the command current given to the variable damper element 20 from the first current value to a second current value that is greater than the first current value while inclining on the time axis. As a result, the command current value rises slowly from the first current value to the second current value at the peak of the relative displacement, so that the vibration of the driver's seat 5S relative to the floor 5F can be quickly converged.

[0087] 3, the variable damper element 20 in this embodiment has a magnetorheological fluid 27 and a coil 25 that applies magnetism to the magnetorheological fluid 27. This makes it possible to easily adjust the damping force of the variable damper element 20 by passing electricity through the coil 25.

[0088] 6(B) and 6(C), the controller 50 controls the variable damper element 20 so that a first damping force is applied in the section from the origin to the peak of the waveform of the relative displacement amount detected by the displacement sensor 41, and controls the variable damper element 20 so that a second damping force is applied in the section from the peak to the origin of the waveform of the relative displacement amount. This makes it possible to absorb impacts and quickly converge vibrations, improving the ride comfort when going over steps while the wheel loader 1 is traveling.

[0089] <Additional Notes> The above-described embodiment includes the following technical ideas.

[0090] (Supplementary Note 1) A work vehicle having a work machine, comprising: a floor; a driver's seat arranged on the floor; a seat suspension arranged between the floor and the driver's seat and having a variable damper element capable of switching a damping force between at least a first damping force and a second damping force greater than the first damping force; a displacement sensor that detects a relative displacement amount of the driver's seat with respect to the floor; and a controller that switches the damping force of the variable damper element from the first damping force to the second damping force when a peak value of the relative displacement amount detected by the displacement sensor is greater than a first predetermined value.

[0091] (Appendix 2) The work vehicle described in Appendix 1 further includes an acceleration sensor that detects acceleration of the floor in the vertical direction, and the controller switches the damping force of the variable damper element from the second damping force to the first damping force when the absolute value of a first peak in the acceleration of the floor detected by the acceleration sensor is greater than the absolute value of a second peak immediately before the first peak.

[0092] (Supplementary Note 3) The work vehicle according to Supplementary Note 1 or Supplementary Note 2, wherein the controller switches the damping force of the variable damper element from the first damping force to the second damping force when it is determined that the relative displacement amount detected by the displacement sensor becomes larger than the first predetermined value and that the relative displacement amount has changed from increasing to decreasing.

[0093] (Supplementary Note 4) The work vehicle according to any one of Supplementary Note 1 to Supplementary Note 3, wherein the controller switches the damping force of the variable damper element from the second damping force to the first damping force when an absolute value of the peak of the relative displacement amount becomes less than a second predetermined value that is smaller than the first predetermined value.

[0094] (Supplementary Note 5) The work vehicle according to any one of Supplementary Note 1 to Supplementary Note 4, wherein the controller switches the damping force of the variable damper element from the first damping force to the second damping force by increasing, with an inclination on a time axis, a value of a command current given to the variable damper element from a first current value to a second current value greater than the first current value.

[0095] (Supplementary Note 6) The work vehicle according to any one of Supplementary Note 1 to Supplementary Note 5, wherein the variable damper element includes a magnetorheological fluid and a coil that forms a magnetic field that acts on the magnetorheological fluid.

[0096] (Supplementary Note 7) A system for a work vehicle having a work machine, the system including a work vehicle comprising: a floor; a driver's seat arranged on the floor; a seat suspension arranged between the floor and the driver's seat and having a variable damper element capable of switching damping force between at least a first damping force and a second damping force greater than the first damping force; a displacement sensor that detects a relative displacement amount of the driver's seat with respect to the floor; and a controller that switches the damping force of the variable damper element from the first damping force to the second damping force when a peak value of the relative displacement amount detected by the displacement sensor is greater than a first predetermined value.

[0097] (Appendix 8) A control method for a work vehicle having a work machine, a floor, a driver's seat arranged on the floor, a seat suspension arranged between the floor and the driver's seat and having a variable damper element capable of switching damping force between at least a first damping force and a second damping force greater than the first damping force, and a displacement sensor that detects a relative displacement amount of the driver's seat with respect to the floor, the control method for a work vehicle comprising: a step of acquiring a relative displacement amount of the driver's seat with respect to the floor; a step of determining whether a peak value of the relative displacement amount detected by the displacement sensor is greater than a first predetermined value; and a step of switching the damping force of the variable damper element from the first damping force to the second damping force when it is determined that the peak value is greater than the first predetermined value.

[0098] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0099] REFERENCE SIGNS LIST 1 Wheel loader, 2 Traveling body, 3 Work machine, 4 Front wheel, 5 Cab, 5F Floor, 5S Cab, 6 Engine room, 7 Rear wheel, 9 Steering cylinder, 10 Body frame, 11 Front frame, 12 Rear frame, 13 Connecting shaft, 14 Boom, 15 Bucket, 16 Lift cylinder, 17 Bucket cylinder, 18 Bell crank, 20 Variable damper element, 21 Cylinder, 21A First fluid chamber, 21B Second fluid chamber, 21C Gas chamber, 22 Piston, 22a Annular orifice, 23 Piston rod, 24 Diaphragm, 25 Coil, 26 Wiring, 27 Magnetorheological fluid, 28 Seal bearing, 30 Elastic member, 40 Seat suspension, 41 Displacement sensor, 42 Current adjustment device, 43 Acceleration sensor, 50 Controller, 51 Displacement information acquisition unit, 52 Displacement information determination unit, 53 damping force control unit, 54 acceleration information acquisition unit, 55 acceleration information determination unit, 56 memory, ST step.

Claims

1. A work vehicle having a working machine, comprising: a floor; a driver's seat arranged on the floor; a seat suspension arranged between the floor and the driver's seat and having a variable damper element capable of switching damping force between at least a first damping force and a second damping force greater than the first damping force; a displacement sensor that detects the relative displacement of the driver's seat with respect to the floor; and a controller that switches the damping force of the variable damper element from the first damping force to the second damping force when the peak value of the relative displacement detected by the displacement sensor is greater than a first predetermined value.

2. A work vehicle as described in claim 1, further comprising an acceleration sensor that detects acceleration of the floor in the vertical direction, and wherein the controller switches the damping force of the variable damper element from the second damping force to the first damping force when the absolute value of a first peak in the acceleration of the floor detected by the acceleration sensor is greater than the absolute value of a second peak immediately preceding the first peak.

3. A work vehicle as described in claim 1, wherein the controller switches the damping force of the variable damper element from the first damping force to the second damping force when it determines that the relative displacement amount detected by the displacement sensor becomes greater than the first predetermined value and that the absolute value of the relative displacement amount has changed from an increase to a decrease.

4. A work vehicle as described in claim 1, wherein the controller switches the damping force of the variable damper element from the second damping force to the first damping force when the absolute value of the peak of the relative displacement amount becomes less than a second predetermined value which is smaller than the first predetermined value.

5. A work vehicle as described in claim 1, wherein the controller switches the damping force of the variable damper element from the first damping force to the second damping force by increasing the value of a command current given to the variable damper element from a first current value to a second current value greater than the first current value while inclining on the time axis.

6. The work vehicle according to claim 1, wherein the variable damper element comprises a magnetorheological fluid and a coil that forms a magnetic field acting on the magnetorheological fluid.

7. A system for a work vehicle having a working machine, comprising: a floor; a driver's seat arranged on the floor; a seat suspension arranged between the floor and the driver's seat and having a variable damper element capable of switching damping force between at least a first damping force and a second damping force greater than the first damping force; a displacement sensor that detects the relative displacement of the driver's seat with respect to the floor; and a controller that switches the damping force of the variable damper element from the first damping force to the second damping force when the peak value of the relative displacement detected by the displacement sensor is greater than a first predetermined value.

8. A control method for a work vehicle having a work machine, a floor, a driver's seat arranged on the floor, a seat suspension arranged between the floor and the driver's seat and having a variable damper element capable of switching damping force between at least a first damping force and a second damping force greater than the first damping force, and a displacement sensor that detects a relative displacement amount of the driver's seat with respect to the floor, comprising the steps of: acquiring the relative displacement amount of the driver's seat with respect to the floor; determining whether a peak value of the relative displacement amount detected by the displacement sensor is greater than a first predetermined value; and switching the damping force of the variable damper element from the first damping force to the second damping force when it is determined that the peak value is greater than the first predetermined value.

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