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

Abstract

A driver's seat (5S) is disposed above a floor (5F). A seat suspension (40) is disposed between the floor (5F) and the driver's seat (5S) and has a variable damper element (20) that has a damping force capable of being switched between at least a first damping force and a second damping force higher than the first damping force. A displacement sensor (41) detects the amount of relative displacement 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) between the first damping force and the second damping force on the basis of whether a multiplication value where the amount of relative displacement detected by the displacement sensor (41) has been multiplied by a relative speed calculated from the amount of relative displacement is positive or negative.

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] The work vehicle and system including the work vehicle of the present disclosure each include a work implement, 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 a relative displacement amount of the driver's seat with respect to the floor. The controller switches the damping force of the variable damper element between the first damping force and the second damping force based on whether a positive or negative value is obtained by multiplying the relative displacement amount detected by the displacement sensor by a relative velocity calculated from the relative displacement amount.

[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] The amount of relative displacement of the driver's seat with respect to the floor is acquired. The relative velocity is calculated from the amount of relative displacement. It is determined whether the product of the amount of relative displacement and the relative velocity is positive or negative. Based on the result of determining whether the product is positive or negative, the damping force of the variable damper element is switched between a first damping force and 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 the time change in the relative displacement amount and relative speed between the floor of the cab and the driver's seat in the vertical direction. FIG. 6A is a diagram showing the traveling state of a work vehicle, FIG. 6B is a diagram showing the time change in the relative displacement amount between the floor of the cab and the driver's seat during traveling, and FIG. 6C is a diagram showing the time change in a command current value given to a variable damper element. FIG. 7 is a flow diagram showing a control method for a work vehicle according to an embodiment of the present disclosure. FIG. 8 is a diagram showing a modified example of the time change in the command current value given to a variable damper element.

[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. A driver's seat 5S for an operator is disposed inside the operator's cab 5. A handle for steering, levers for operating the work implement 3, various switches, display devices, and the like (not shown) are also disposed inside the operator's cab 5. The engine room 6 is disposed 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 , 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 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.

[0030] The controller 50 is electrically connected to the displacement sensor 41 and the current adjusting device 42. The controller 50 acquires displacement data detected by the displacement sensor 41. The controller 50 controls the current adjusting device 42 based on the displacement data detected by the displacement sensor 41. The controller 50 adjusts the amount of current supplied to the coil 25 of the variable damper element 20 by controlling the current adjusting device 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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, current adjustment device 42, etc. The controller 50 may be stored in a server located remotely from the wheel loader 1.

[0035] 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.

[0036] 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.

[0037] 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 slidable in the axial direction AX relative to the cylinder 21.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 4, the controller 50 includes a displacement information acquisition unit 51, a speed calculation unit 52, a multiplication value calculation unit 53, a multiplication value determination unit 54, a damping force control unit 55, a displacement information determination unit 56, and a memory 57. The displacement information acquisition unit 51 acquires a signal indicating the amount of relative displacement of the driver's seat 5S with respect to the floor 5F detected by the displacement sensor 41.

[0043] The velocity calculation unit 52 calculates the relative velocity of the driver's seat 5S with respect to the floor 5F by differentiating the displacement amount acquired by the displacement information acquisition unit 51. The multiplication value calculation unit 53 multiplies the relative displacement amount acquired by the displacement information acquisition unit 51 by the relative velocity calculated by the velocity calculation unit 52 to calculate a multiplication value.

[0044] The multiplication value determination unit 54 determines whether the multiplication value calculated by the multiplication value calculation unit 53 is a positive value or a negative value. The damping force control unit 55 outputs a command current for controlling the current adjustment device 42 based on the determination result of whether the multiplication value determined by the multiplication value determination unit 54 is a positive value or a negative value.

[0045] When the damping force control unit 55 obtains a determination result from the multiplication value determination unit 54 that the multiplication value is a positive value, the damping force control unit 55 outputs a command current that sets the damping force of the variable damper element 20 to the first damping force to the current adjustment device 42. In this way, when the controller 50 determines that the multiplication value is a positive value, the damping force of the variable damper element 20 is set to the first damping force.

[0046] Furthermore, when the damping force control unit 55 obtains a determination result from the multiplication value determination unit 54 that the multiplication value is a negative value, the damping force control unit 55 outputs a command current that sets the damping force of the variable damper element 20 to the second damping force to the current adjustment device 42. In this way, when the controller 50 determines that the multiplication value is a negative value, the damping force of the variable damper element 20 is set to the second damping force.

[0047] The displacement information determination unit 56 determines whether the absolute value of the peak of the relative displacement amount acquired by the displacement information acquisition unit 51 is less than a predetermined value. When making this determination, the displacement information determination unit 56 refers to the predetermined value stored in the memory 57.

[0048] The damping force control unit 55 outputs a command current to control the current adjustment device 42 based on the determination result of the displacement information determination unit 56. When the damping force control unit 55 obtains a determination result from the displacement information determination unit 56 that the absolute value of the peak of the relative displacement amount is less than a predetermined value, the damping force control unit 55 outputs a command current to the current adjustment device 42 that sets the damping force of the variable damper element 20 to the first damping force. In this way, when the controller 50 determines that the absolute value of the peak of the relative displacement amount is less than the predetermined value, the controller 50 sets the damping force of the variable damper element 20 to the first damping force.

[0049] 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 55. When the current adjusting device 42 obtains a command current from the damping force control unit 55 to cause the variable damper element 20 to have a first damping force, for example, the current adjusting device 42 does not supply current to the coil 25 of the variable damper element 20 (cuts off the supply of current). On the other hand, when the current adjusting device 42 obtains a command current from the damping force control unit 55 to cause the variable damper element 20 to have a second damping force, for example, the current adjusting device 42 supplies current to the coil 25 of the variable damper element 20. 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 current to the coil 25 of the variable damper element 20.

[0050] 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.

[0051] <Principle of Damping Force Control> Based on the skyhook theory, the controller 50 shown in Fig. 2 controls the damping force of the variable damper element 20 so that it is greater than in other states when the amount of relative displacement in the up-down direction Y between the driver's seat 5S and the floor 5F transitions from the peak of the displacement to the origin (0) of the displacement. This will be described below.

[0052] The Skyhook theory assumes a model in which an object is suspended in mid-air from an imaginary line by a damper. The state that the Skyhook theory aims to achieve is a state in which the object is connected to the ground by a spring and to the imaginary line by a damper.

[0053] In this model, the damping force Fd of the damper can be simplified and expressed by the following equation (1).

[0054] Fd=CsVs (1) In equation (1), Cs is the damping coefficient of the damper, and Vs is the displacement velocity of the object in the vertical direction Y.

[0055] However, in reality, no imaginary line exists, so the above model is replaced with a state in which the object (driver's seat 5S) and the base (floor 5F) are connected by a variable damper element 20 and an elastic member 30, as shown in Figure 2.

[0056] The damping force Fd in this state is expressed by the following equation (2) based on equation (1): Fd = Cvar(t) (Vs - Vb) (2) In equation (2), Vs is the displacement speed of the object (driver's seat 5S) in the vertical direction Y, and Vb is the displacement speed of the base (floor 5F) in the vertical direction Y.

[0057] In this embodiment, the discriminants for Cvar(t) in equation (2) are the following equations (3) and (4).

[0058] Cvar(t) = Cmax((Xs - Xb) (Vs - Vb) < 0) (3) Cvar(t) = Cmin((Xs - Xb) (Vs - Vb) ≥ 0) (4) In equations (3) and (4), Xs is the displacement of the object (driver's seat 5S) in the vertical direction Y, and Xb is the displacement of the base (floor 5F) in the vertical direction Y. Therefore, (Xs - Xb) is the relative displacement of the object (driver's seat 5S) in the vertical direction Y with respect to the base (floor 5F). Also, (Vs - Vb) is the relative velocity of the object (driver's seat 5S) in the vertical direction Y with respect to the base (floor 5F).

[0059] By using the above equations (3) and (4), it is possible to determine the state in which the amount of relative displacement of the driver's seat 5S with respect to the floor 5F in the vertical direction Y moves from the peak of the displacement to the origin of the displacement. This will be explained using FIG.

[0060] 5 is a diagram showing the time-dependent change in the relative displacement and relative velocity between the floor of the cab and the driver's seat in the vertical direction Y. In FIG. 5, the solid curve indicates the relative displacement between the floor 5F and the driver's seat 5S. The dashed curve indicates the relative velocity between the floor 5F and the driver's seat 5S.

[0061] 5, it is assumed that the amount of relative displacement of the driver's seat 5S in the vertical direction Y with respect to the floor 5F changes like a sine curve. In this case, since the relative velocity is obtained by differentiating the amount of relative displacement, the relative velocity of the driver's seat 5S in the vertical direction Y with respect to the floor 5F changes like a cosine curve.

[0062] The origin of the waveform of the relative displacement (the point where the waveform intersects with 0) indicates the relative position of the driver's seat 5S with respect to the floor 5F in a stationary state. The origin of the relative velocity (the point where the waveform intersects with 0) indicates the relative velocity of the driver's seat 5S with respect to the floor 5F in a stationary state.

[0063] Here, the case where the multiplication value (Xs-Xb) (Vs-Vb) obtained by multiplying the relative displacement amount (Xs-Xb) of the driver's seat 5S with respect to the floor 5F in the vertical direction Y by the relative velocity (Vs-Vb) of the driver's seat 5S with respect to the floor 5F in the vertical direction Y is negative is shown as region RA in Figure 5. Also, the case where the multiplication value (Xs-Xb) (Vs-Vb) is positive is shown as region RB in Figure 5.

[0064] It can be seen that region RA is a region where the relative displacement amount (Xs-Xb) in the vertical direction Y shifts from the peak of the displacement to the origin of the displacement over time, and region RB is a region where the relative displacement amount (Xs-Xb) in the vertical direction Y shifts from the origin of the displacement to the peak of the displacement over time.

[0065] From the above, by using the discriminants (3) and (4), it is possible to determine the state in which the amount of relative displacement in the vertical direction Y between the driver's seat 5S and the floor 5F moves from the peak of the displacement to the origin of the displacement. In other words, depending on whether the multiplied value (Xs-Xb) (Vs-Vb) is positive or negative, it is possible to determine the state in which the amount of relative displacement in the vertical direction Y between the driver's seat 5S and the floor 5F moves from the peak of the displacement to the origin of the displacement.

[0066] In this embodiment, the controller 50 switches the damping force of the variable damper element 20 between the first damping force and the second damping force based on whether the multiplication value (Xs-Xb) (Vs-Vb) is positive or negative. The controller 50 switches between supplying and cutting off current to the coil 25 of the variable damper element 20, for example, based on whether the multiplication value (Xs-Xb) (Vs-Vb) is positive or negative.

[0067] If the controller 50 determines that the multiplication value (Xs-Xb) (Vs-Vb) is a negative value (i.e., if it determines that the multiplication value is in the region RA in FIG. 5), it sets the damping force of the variable damper element 20 to a second damping force that is greater than the first damping force. If the controller 50 determines that the multiplication value (Xs-Xb) (Vs-Vb) is a negative value, it supplies current to the coil 25 of the variable damper element 20, for example, to turn it on.

[0068] If the controller 50 determines that the multiplication value (Xs-Xb) (Vs-Vb) is a positive value (i.e., if the controller 50 determines that the multiplication value is in region RB in FIG. 5), the damping force of the variable damper element 20 is set to a first damping force that is smaller than the second damping force. If the controller 50 determines that the multiplication value (Xs-Xb) (Vs-Vb) is a positive value, the controller 50 cuts off the supply of current to the coil 25 of the variable damper element 20, for example, to set it to an off state.

[0069] <Method of Controlling a Work Vehicle> Next, a method of controlling a work vehicle in this embodiment will be described with reference to Figs. 6 and 7, using as an example a state in which the wheel loader 1 goes over a step while traveling.

[0070] 6A is a diagram showing the state of travel of a work vehicle, FIG. 6B is a diagram showing the change over time in the amount of relative displacement between the floor of the cab and the driver's seat while the work vehicle is traveling, and FIG. 6C is a diagram showing the change over time in the command current value applied to the variable damper element. FIG. 7 is a flow diagram showing a control method for a work vehicle according to one embodiment of the present disclosure.

[0071] As shown in Figure 6(A), while the wheel loader 1 is traveling forward, there are cases where the front wheels 4 of the wheel loader 1 run up on a step ST, and then the rear wheels 7 run up on the step ST. In this case, the amount of relative displacement 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 6(B).

[0072] The arrow AR1 shown in Figure 6(B) indicates 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 6(B) indicates the point in time when the rear wheels 7 of the wheel loader 1 run up onto the step ST.

[0073] As shown in Figure 6 (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.

[0074] 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.

[0075] In this embodiment, the amount of relative displacement (Xs-Xb) 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.

[0076] 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 S1: FIG. 7 ). The displacement information acquisition unit 51 outputs the signal indicating the relative displacement amount to the speed calculation unit 52.

[0077] The velocity calculation unit 52 calculates the relative velocity (Vs-Vb) of the driver's seat 5S in the up-down direction Y with respect to the floor 5F by differentiating the relative displacement amount (step S2: FIG. 7). The velocity calculation unit 52 outputs a signal indicating the calculated relative velocity to the multiplication value calculation unit 53.

[0078] The multiplication value calculation unit 53 calculates the multiplication value (Xs-Xb) (Vs-Vb) by multiplying the relative displacement amount (Xs-Xb) acquired by the displacement information acquisition unit 51 by the relative velocity (Vs-Vb) calculated by the velocity calculation unit 52 (step S3: FIG. 7). The multiplication value calculation unit 53 outputs a signal indicating the calculated multiplication value to the multiplication value determination unit 54.

[0079] The multiplication value determination unit 54 determines whether the multiplication value (Xs-Xb) (Vs-Vb) calculated by the multiplication value calculation unit 53 is 0 or a positive value (step S4: FIG. 7). The multiplication value determination unit 54 outputs a signal indicating the determination result to the damping force control unit 55.

[0080] The damping force control unit 55 outputs a command current for controlling the current adjusting device 42 based on the determination result of the multiplication value determination unit 54 .

[0081] If the multiplied value is 0 or a positive value, the damping force control unit 55 outputs to the current adjusting device 42 a command current value that causes the damping force of the variable damper element 20 to become a small first damping force (step S5: FIG. 7). If the multiplied value is 0 or a positive value, the damping force control unit 55 controls the current adjusting device 42 to, for example, cut off the supply of current to the coil 25 of the variable damper element 20, as shown in FIG. 6(C).

[0082] On the other hand, if the multiplied value is negative, the damping force control unit 55 outputs to the current adjusting device 42 a command current value that causes the damping force of the variable damper element 20 to become a larger second damping force (step S6: FIG. 7). If the multiplied value is negative, the damping force control unit 55 controls the current adjusting device 42 to supply current to the coil 25 of the variable damper element 20, for example, as shown in FIG. 6(C).

[0083] As described above, the current supply to the coil 25 of the variable damper element 20 is controlled to be turned on and off. As a result, as shown in Figures 6(B) and 6(C), the current adjusting device 42 can be controlled to supply current to the coil 25 only when the waveform of the relative displacement amount transitions from its peak to its origin. Also, the current adjusting device 42 can be controlled to cut off the current to the coil 25 when the waveform of the relative displacement amount transitions from its origin to its peak.

[0084] In the above control, the displacement information acquisition unit 51 shown in Fig. 4 outputs a signal indicating the acquired relative displacement amount to the displacement information determination unit 56. The displacement information determination unit 56 determines whether the absolute value of the peak of the relative displacement amount acquired by the displacement information acquisition unit 51 is less than a predetermined value. When making this determination, the displacement information determination unit 56 refers to the predetermined value stored in the memory 57.

[0085] If the displacement information determination unit 56 determines that the absolute value of the peak of the relative displacement amount is less than a predetermined value, the displacement information determination unit 56 outputs a signal indicating the determination result to the damping force control unit 55. If the absolute value of the peak of the relative displacement amount is less than the predetermined value, the damping force control unit 55 outputs to the current adjustment device 42 a command current value such that the damping force of the variable damper element 20 becomes a small first damping force. As a result, when the vibration of the driver's seat 5S relative to the floor 5F has converged, the damping force of the variable damper element 20 can be maintained at the first damping force by, for example, cutting off the supply of current to the coil 25.

[0086] Although the above description has been given of the case where the rear wheel 7 runs over the step ST as the second running over of the step ST, the second running over of the step may also be the case where the front wheel 4 runs over the second step. Furthermore, similar control may also be executed for the third and subsequent running over of steps.

[0087] 8, the waveform of each of the upper peak portion (S1) and the lower peak portion (S2) in the time change of the command current value applied to the variable damper element may transition to or from the peak along a smooth curve. Furthermore, as shown by arrow S3, the peak value of the command current value in the ON state may be an intermediate current value between the peak value in another ON state and the peak value in the OFF state. Furthermore, as shown by arrow S4, the waveform of the command current value may be inclined when rising from the OFF state to the ON state.

[0088] <Effects> Next, the effects of this embodiment will be described.

[0089] In this embodiment, the damping force of the variable damper element 20 is switched between a first damping force and a second damping force based on the positive or negative sign of a multiplication value obtained by multiplying the amount of relative displacement detected by the displacement sensor 41 by the relative velocity calculated from that amount of relative displacement. The positive or negative sign of the multiplication value makes it possible to determine whether the relative displacement of the driver's seat 5S with respect to the floor 5F is in region RA or region RB shown in FIG. 5 . This allows the damping force of the variable damper element 20 to be switched between the first damping force and the second damping force in region RA and region RB, enabling shock absorption and quick convergence of vibration. This improves ride comfort when the wheel loader 1 goes over steps while traveling.

[0090] Furthermore, the above control is possible by detecting the amount of relative displacement with the displacement sensor 41, and other sensors are not required for the above control, so the configuration can be simplified.

[0091] 4, when the controller 50 determines that the multiplied value is negative, it sets the damping force of the variable damper element 20 to a second damping force that is greater than the first damping force. This allows the damping force of the variable damper element 20 to be large in an area RA where the relative displacement waveform transitions from its peak to the origin, as shown in FIG. 5, so that the vibration of the driver's seat 5S can be quickly converged.

[0092] 4, when the controller 50 determines that the multiplied value is a positive value, the damping force of the variable damper element 20 is set to a first damping force that is smaller than the second damping force. This makes it possible to reduce the damping force of the variable damper element 20 in a region RB where the waveform of the relative displacement transitions from the origin to the peak, as shown in FIG. 5, thereby facilitating impact absorption.

[0093] 4, in this embodiment, when the absolute value of the peak of the relative displacement is less than a predetermined value, the controller 50 sets the damping force of the variable damper element 20 to a small first damping force. This makes it possible to turn off the power supply to the variable damper element 20 when the vibration of the driver's seat 5S is weak.

[0094] 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.

[0095] 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.

[0096] <Additional Notes> The above-described embodiment includes the following technical ideas.

[0097] (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 between the first damping force and the second damping force based on the sign of a multiplication value obtained by multiplying the relative displacement amount detected by the displacement sensor by a relative speed calculated from the relative displacement amount.

[0098] (Supplementary Note 2) The work vehicle according to Supplementary Note 1, wherein the controller sets the damping force of the variable damper element to the second damping force when it is determined that the multiplied value is a negative value.

[0099] (Supplementary Note 3) The work vehicle according to Supplementary Note 1 or Supplementary Note 2, wherein the controller sets the damping force of the variable damper element to the first damping force when it is determined that the multiplied value is a positive value.

[0100] (Supplementary Note 4) The work vehicle according to any one of Supplementary Note 1 to Supplementary Note 3, wherein the controller sets the damping force of the variable damper element to the first damping force when an absolute value of a peak in the amount of relative displacement becomes less than a predetermined value.

[0101] (Supplementary Note 5) The work vehicle according to any one of Supplementary Note 1 to Supplementary Note 4, wherein the variable damper element includes a magnetorheological fluid and a coil that forms a magnetic field that acts on the magnetorheological fluid.

[0102] (Supplementary Note 6) The work vehicle according to any one of Supplementary Note 1 to Supplementary Note 5, wherein the controller controls the variable damper element so as to provide the first damping force in a section from an origin to a peak of a waveform of the relative displacement amount detected by the displacement sensor, and controls the variable damper element so as to provide the second damping force in a section from a peak to the origin of a waveform of the relative displacement amount detected by the displacement sensor.

[0103] (Supplementary Note 7) A system including a work vehicle having a work implement, 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 between the first damping force and the second damping force based on the sign of a multiplication value obtained by multiplying the relative displacement amount detected by the displacement sensor by a relative speed calculated from the relative displacement amount.

[0104] (Appendix 8) A control method for a work vehicle having a work implement, 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 the steps of: acquiring the relative displacement amount of the driver's seat with respect to the floor; calculating a relative velocity from the relative displacement amount; determining whether a product of the relative displacement amount and the relative velocity is positive or negative; and switching the damping force of the variable damper element between the first damping force and the second damping force based on a result of determining whether the multiplied value is positive or negative.

[0105] 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.

[0106] 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, 50 Controller, 51 Displacement information acquisition unit, 52 Speed ​​calculation unit, 53 Multiplication value calculation unit, 54 multiplication value determination unit, 55 damping force control unit, 56 displacement information determination unit, 57 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 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 between the first damping force and the second damping force based on the positive or negative sign of a multiplication value obtained by multiplying the relative displacement amount detected by the displacement sensor by a relative speed calculated from the relative displacement amount.

2. A work vehicle according to claim 1, wherein the controller sets the damping force of the variable damper element to the second damping force when it determines that the multiplied value is a negative value.

3. A work vehicle according to claim 1, wherein the controller sets the damping force of the variable damper element to the first damping force when it is determined that the multiplied value is a positive value.

4. A work vehicle according to claim 1, wherein the controller sets the damping force of the variable damper element to the first damping force when the absolute value of the peak of the relative displacement amount becomes less than a predetermined value.

5. A 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.

6. A work vehicle as described in claim 1, wherein the controller controls the variable damper element so as to provide the first damping force in the section from the origin to the peak of the waveform of the relative displacement amount detected by the displacement sensor, and controls the variable damper element so as to provide the second damping force in the section from the peak to the origin of the waveform of the relative displacement amount detected by the displacement sensor.

7. A system including 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 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 between the first damping force and the second damping force based on the positive or negative sign of a multiplication value obtained by multiplying the relative displacement amount detected by the displacement sensor by a relative speed calculated from the relative displacement amount.

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; calculating a relative velocity from the relative displacement amount; determining whether a multiplied value of the relative displacement amount and the relative velocity is positive or negative; and switching the damping force of the variable damper element between the first damping force and the second damping force based on the result of determining whether the multiplied value is positive or negative.

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