Work vehicles

Abstract

To provide a work vehicle that can improve the work efficiency of the forklift operation when pulling out a load from a pallet, regardless of the work site environment. [Solution] A wheel loader 1 with pallet forks is characterized by having a switchable valve 74 that can switch between a float position 741 that connects the rod chamber 125A and bottom chamber 125B of the fork cylinder 125 that drives the forks 2 to the hydraulic oil tank 71, and a float release position 742 that blocks the communication between the rod chamber 125A and bottom chamber 125B of the fork cylinder 125 and the hydraulic oil tank 71, thereby enabling the operation of the fork cylinder 125 by the operating lever 334, and a controller 9 that controls the switchable valve 74.

Description

Technical Field

[0001] The present invention relates to a work vehicle provided with a work device.

Background Art

[0002] A work vehicle performs various operations using a work device mounted on the front portion of the vehicle body. For example, a work vehicle equipped with forks for transporting pallets on which loads are placed performs cargo handling operations in which the forks are inserted into insertion spaces of the pallets, the pallets are lifted, and the pallets are lowered at predetermined positions. When pulling the forks out of the insertion spaces of the pallets, the forks need to be parallel to the pallets so that the forks do not come into contact with the top surfaces of the insertion spaces of the pallets. However, when the pallets are not placed horizontally such as during work on sloped ground, it is difficult to keep the forks always parallel to the pallets.

[0003] For example, Patent Document 1 discloses a forklift in which a sensor for detecting an obstacle is attached to the tip of a fork, and when the sensor detects an obstacle obliquely above or obliquely below the tip of the fork, the fork is tilted, whereby contact of the fork with the top surface or the bottom surface of the insertion space of the pallet can be avoided.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0005] However, if the technology described in Patent Document 1 is applied to a wheel loader with pallet forks used for loading and unloading operations at sites handling soil and compost, the sensors attached to the tips of the forks may become buried and contaminated in the soil and compost, making it impossible to properly detect obstacles such as the top surface of the insertion space, and thus making it impossible to avoid contact of the forks with the top surface of the pallet insertion space.

[0006] Therefore, the object of the present invention is to provide a work vehicle that is not affected by the working environment and can improve the workability of the forklift operation from a pallet on which a load is placed. [Means for solving the problem]

[0007] To achieve the above objective, the present invention provides a work vehicle comprising a vehicle body, an arm member attached to the front of the vehicle body, a fork attached to the tip of the arm member via a backrest, an attachment hydraulic cylinder for rotating the fork vertically relative to the tip of the arm member, and an operating lever for operating the attachment hydraulic cylinder, characterized in that the work vehicle comprises a switching valve that can be switched between a float position that connects the rod chamber and bottom chamber of the attachment hydraulic cylinder to a hydraulic oil tank, and a float release position that blocks communication between the rod chamber and bottom chamber of the attachment hydraulic cylinder and the hydraulic oil tank, thereby enabling operation of the attachment hydraulic cylinder by the operating lever, and a controller that controls the switching valve. [Effects of the Invention]

[0008] According to the present invention, the workability of the forklift operation from a pallet on which a load is placed can be improved, regardless of the working environment. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments. [Brief explanation of the drawing]

[0009] [Figure 1]This is an external side view showing an example configuration of a wheel loader according to the first embodiment of the present invention. [Figure 2] This is an enlarged perspective view showing one example configuration of a work device. [Figure 3A] This is a schematic diagram showing one example of a fork configuration. [Figure 3B] This is a schematic diagram showing other examples of fork configurations. [Figure 4] This is a partially enlarged perspective view showing an example of the configuration of the driver's unit. [Figure 5] This diagram shows an example configuration of a fork drive system, specifically the system configuration when the switching valve is switched to the float release position. [Figure 6] This diagram shows an example configuration of a fork drive system, specifically the system configuration when the switching valve is switched to the float position. [Figure 7A] This is a functional block diagram showing the functions of the controller according to the first embodiment. [Figure 7B] This flowchart shows the processing flow executed by the controller according to the first embodiment. [Figure 8] This is an explanatory diagram illustrating how the fork is pulled out from the pallet. [Figure 9] This is a partially enlarged perspective view showing one example configuration of a work apparatus according to the second embodiment of the present invention. [Figure 10] This is a system configuration diagram showing one example of the configuration of a fork drive system according to a second embodiment of the present invention. [Figure 11] This is a functional block diagram showing the functions of the controller according to the second embodiment. [Figure 12] This is a flowchart showing the processing flow executed by the controller according to the second embodiment. [Modes for carrying out the invention]

[0010] Hereinafter, as an example of one embodiment of the work vehicle according to each embodiment of the present invention, a wheel loader with pallet forks will be described.

[0011] <First Embodiment> First, a wheel loader 1 according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 8.

[0012] (Configuration of Wheel Loader 1) The configuration of the wheel loader 1 will be described with reference to FIGS. 1 to 4.

[0013] FIG. 1 is an external side view showing an example of the configuration of the wheel loader 1 according to the first embodiment of the present invention. FIG. 2 is an enlarged perspective view showing an example of the configuration of a working device 12. FIG. 3A is a schematic view showing an example of the configuration of a fork 2. FIG. 3B is a schematic view showing another example of the configuration of the fork 2. FIG. 4 is a partially enlarged perspective view showing an example of the configuration of an operation unit 13.

[0014] As shown in FIG. 1, the wheel loader 1 is an articulated work vehicle that is steered by the vehicle body being bent at the vicinity of the center. A front frame 1A, which is the front portion of the vehicle body, and a rear frame 1B, which is the rear portion of the vehicle body, are connected by a center joint 10 so as to be rotatable in the left-right direction, and the front frame 1A bends in the left-right direction relative to the rear frame 1B.

[0015] In the following description, of the left-right directions that correspond to the vehicle width direction of the vehicle body, the direction on the left side with respect to the forward traveling direction is defined as "left direction", and the direction on the right side with respect to the forward traveling direction is defined as "right direction".

[0016] The vehicle body is provided with four wheels 11, where two wheels 11 are respectively provided on the left and right sides of the front frame 1A as front wheels 11A, and the remaining two wheels 11 are respectively provided on the left and right sides of the rear frame 1B as rear wheels 11B. In FIG. 1, only the left front wheel 11A and the left rear wheel 11B among the four wheels 11 are shown.

[0017] At the front portion of the front frame 1A, a hydraulically driven working device 12 for performing cargo handling work of lifting a pallet P (see FIG. 8) for cargo transportation and lowering it at a predetermined position is attached.

[0018] As shown in Figures 1 and 2, the work device 12 includes a lift arm 121 as an arm member rotatably mounted to the front frame 1A, two lift arm cylinders 122 for driving the lift arm 121, a fork 2 that is inserted into and removed from the insertion space of the pallet P, a backrest 123 that supports the fork 2, a connecting member 124 that is rotatably mounted to the tip of the lift arm 121 and connects the lift arm 121 and the backrest 123, a fork cylinder 125 as an attachment hydraulic cylinder that rotates the fork 2 vertically relative to the tip of the lift arm 121, and a bell crank 126 that is rotatably connected to the lift arm 121 and constitutes a link mechanism between the connecting member 124 and the fork cylinder 125.

[0019] Although the two lift arm cylinders 122 are arranged side by side in the left-right direction of the vehicle body, only the lift arm cylinder 122 located on the left side is shown in Figures 1 and 2.

[0020] The lift arm 121 rotates vertically relative to the front frame 1A as hydraulic fluid flows in and out of the two lift arm cylinders 122, causing each rod to extend and retract.

[0021] As shown in Figure 2, the fork 2 has a pair of insertion / removal sections 21 arranged side by side at a predetermined distance apart in the left-right direction of the vehicle body, and a connecting section 22 that connects the pair of insertion / removal sections 21. Each pair of insertion / removal sections 21 is made by bending a long, narrow plate and includes an insertion plate section 21A which is inserted into the insertion space of the pallet P, and a mounting plate section 21B which is erected from one end (base end) of the insertion plate section 21A and attached to the backrest 123.

[0022] As shown in Figures 3A and 3B, the insertion plate portion 21A has a top surface 211 on which the load is placed that is flat from the base to the tip, without curving, so that it does not come into contact with the pallet P when it is inserted into or removed from the insertion space of the pallet P. On the other hand, the bottom surface 212, which is opposite to the top surface 211, has a tip that is curved downwards in an arc shape. In other words, the tip of the insertion plate portion 21A is formed with the top surface 211 being a flat surface and the bottom surface 212 being a curved surface.

[0023] In the example shown in Figure 3A, the tip of the insertion plate portion 21A is rounded, while in the example shown in Figure 3B, the tip of the insertion plate portion 21A is pointed. However, as long as the bottom surface 212 of the tip of the insertion plate portion 21A is curved, there are no particular restrictions on the shape of the tip of the insertion plate portion 21A.

[0024] In this way, the bottom surface 212 at the tip of the fork 2 is formed in an arc shape that curves downwards, making it less likely for the fork 2 to get caught on steps or other obstacles in the ground when inserting or removing it.

[0025] The fork 2 moves vertically in conjunction with the drive of the lift arm 121 and also tilts relative to the vehicle body via the lift arm 121. The tilting motion of the fork 2 is due to the rotation of the connecting member 124.

[0026] The connecting member 124 rotates vertically relative to the lift arm 121 as hydraulic fluid flows in and out of the fork cylinder 125, causing the rod 125C (see Figures 5 and 6) to extend and retract. As a result, the fork 2, together with the backrest 123, can tilt forward towards the vehicle body (forward tilt) or backward towards the vehicle body (rearward tilt).

[0027] In this embodiment, as shown in Figure 2, a marker 61 indicating the height position of the fork 2 relative to the ground surface is provided at the lower left end of the backrest 123. The marker 61 is, for example, a leveler, which protrudes from the left side of the backrest 123 and can be visually seen by the operator from the driver's unit 13 (see Figure 1) located on the rear frame 1B. The "ground surface" is the surface that the lower surface of the bottom of the pallet P on which the load X is stacked contacts, or in other words, the upper surface Z of the pallet storage area Y (see Figure 8).

[0028] Specifically, the sign 61 includes a bracket 611 fixed to the backrest 123, a rotating rod 612 rotatably attached to the bracket 611, and a connecting pin 613 connecting the bracket 611 and the rotating rod 612.

[0029] The connecting pin 613 is the rotation center of the rotating rod 612, but it is positioned towards the rear (vehicle side) of the center of the rotating rod 612. When no external force is acting on the rotating rod 612, due to the relationship of moments, the tip of the rotating rod 612 rotates downward. The operator can confirm the height position of the fork 2 by observing the movement of this rotating rod 612.

[0030] In this embodiment, the sign 61 is provided protruding from the lower left end of the backrest 123, but it is sufficient for it to protrude from one side of the backrest 123 in the left-right direction (vehicle width direction), and for example, it may protrude from the right side of the backrest 123. Furthermore, the configuration of the sign 61 does not necessarily have to include the mechanism described above, and it is sufficient for it to have a mechanism that allows the operator to see it from the driver's seat 13.

[0031] As shown in Figure 1, the rear frame 1B is provided with a driver's compartment 13 where the operator sits, a machine room 14 that houses various equipment necessary for driving the wheel loader 1, and a counterweight 15 that maintains balance with the work equipment 12 to prevent the vehicle body from tilting. In the rear frame 1B, the driver's compartment 13 is located at the front, the machine room 14 is located at the rear of the driver's compartment 13, and the counterweight 15 is located at the lower rear end.

[0032] In this embodiment, the driver's unit 13 has a canopy structure in which the area above the driver's seat 32 is covered by a canopy 31 supported by a pair of vertically extending pillars, and the front, back, left, and right sides are open. In addition to the driver's seat 32 in which the operator sits, the driver's unit 13 is also equipped with an operating unit 33 for operating the wheel loader 1 and an alarm device 34 to alert the operator.

[0033] As shown in Figure 4, the operating unit 33 includes an accelerator pedal 331A for driving the vehicle, a pair of brake pedals 331B for stopping the vehicle, a steering wheel 332 for steering, a console 333 on which various operating switches and a monitor displaying the driving speed are located, work levers 334 for operating the two lift arm cylinders 122 and the fork cylinder 125 respectively, and a changeover switch 335 for switching the float function of the fork cylinder 125 on or off.

[0034] Within the driver's compartment 13, the accelerator pedal 331A and a pair of brake pedals 331B are located in front of and below the driver's seat 32, the steering wheel 332 is located above the accelerator pedal 331A and the pair of brake pedals 331B, the console 333 is located in front of the steering wheel 332, and the work control lever 334 is located to the right of the driver's seat 32. Note that the work control lever 334 does not necessarily have to be located to the right of the driver's seat 32; it may be located to the left of the driver's seat 32.

[0035] Furthermore, in the wheel loader 1 according to this embodiment, both the operation of the two lift arm cylinders 122 and the operation of the fork cylinder 125 can be performed with a single operating lever 334. That is, by operating a single operating lever 334, the lifting and lowering of the lift arm 121 and the forward and backward tilting of the fork 2 (connecting member 124) are performed. However, the invention is not limited to this, and separate operating levers may be provided for operating the two lift arm cylinders 122 and for operating the fork cylinder 125.

[0036] The changeover switch 335 is one form of a changeover indicator device for indicating the changeover position of the changeover valve 74, which will be described later. Specifically, the changeover switch 335 is a manual operating device for operating the changeover of the changeover valve 74 to the float position 741, and when it is ON, it enables the float function in the fork cylinder 125, and when it is OFF, it disables the float function in the fork cylinder 125.

[0037] Here, the "float function" in the fork cylinder 125 is a function that allows the fork 2 to be driven (tilted forward) without the operation of the fork 2 by the work operation lever 334 by draining the hydraulic fluid from inside the fork cylinder 125.

[0038] For example, even in situations where the pallet P is not placed horizontally, such as during loading and unloading operations on a slope, and the front of the work device 12 is difficult to see, by activating the float function of the fork cylinder 125, the operator can simply lower the lift arm 121, causing the forks 2 to become horizontal to the insertion opening of the pallet P, thus enabling smooth insertion and removal of the forks 2.

[0039] In this embodiment, the changeover switch 335 includes a first changeover operation unit 335A provided on the upper part of the work operation lever 334 and a second changeover operation unit 335B provided on the handle 332.

[0040] The operator turns on the changeover switch 335 by simultaneously operating the two changeover operation units 335A and 335B. This activates the float function in the fork cylinder 125. By configuring the changeover switch 335 with two changeover operation units 335A and 335B in this way, it is possible to avoid situations where the float function is activated due to unintended operation by the operator.

[0041] Note that the changeover switch 335 does not necessarily have to consist of two changeover operation units 335A and 335B, but may consist of only one changeover operation unit (for example, only the first changeover operation unit 335A or the second changeover operation unit 335B). Also, the arrangement of the first changeover operation unit 335A and the second changeover operation unit 335B does not have to be in the positions shown in Figure 5.

[0042] (Configuration of fork drive system 7) Next, the configuration of the fork drive system 7 will be described with reference to Figures 5 and 6. The fork drive system 7 is a drive system related to the tilting motion of the fork 2.

[0043] Figure 5 shows an example configuration of the fork drive system 7, and is a system configuration diagram when the switching valve 74 is switched to the float release position 74A. Figure 6 shows an example configuration of the fork drive system 7, and is a system configuration diagram when the switching valve 74 is switched to the float position 74B.

[0044] The fork drive system 7 includes a hydraulic oil tank 71 for storing hydraulic oil, a hydraulic pump 72 for pumping and discharging hydraulic oil from the hydraulic oil tank 71, a directional control valve 73 for controlling the flow (direction and flow rate) of hydraulic oil discharged from the hydraulic pump 72 and supplied to the fork cylinder 125, a switching valve 74 for switching the float function of the fork cylinder 125 on or off, and a controller 9 for controlling the switching valve 74.

[0045] The directional control valve 73 is located between the hydraulic fluid tank 71 and the hydraulic pump 72 and the fork cylinder 125.

[0046] When the directional control valve 73 is switched to the first switching position (not shown in the figure), the hydraulic fluid discharged from the hydraulic pump 72 flows into the rod chamber 125A of the fork cylinder 125, and the hydraulic fluid in the bottom chamber 125B of the fork cylinder 125 flows out into the hydraulic fluid tank 71. As a result, the rod 125C of the fork cylinder 125 retracts, and the fork 2 tilts forward toward the front of the vehicle body.

[0047] Furthermore, when the directional control valve 73 is switched to the second switching position (not shown), the hydraulic fluid discharged from the hydraulic pump 72 flows into the bottom chamber 125B of the fork cylinder 125, and the hydraulic fluid in the rod chamber 125A of the fork cylinder 125 flows out into the hydraulic fluid tank 71. As a result, the rod 125C of the fork cylinder 125 extends, and the fork 2 tilts backward toward the driver unit 13.

[0048] The switching valve 74 is electromagnetic and is located on a pair of sub-pipes 701A and 702A that branch off from a pair of main pipes 701 and 702 that connect the directional control valve 73 and the fork cylinder 125. A hydraulic oil tank 71 is connected downstream of the switching valve 74.

[0049] The switching valve 74 switches between a float position 741 and a float release position 742. In the float position 741, the rod chamber 125A and bottom chamber 125B of the fork cylinder 125 are connected to the hydraulic oil tank 71. In the float release position 742, the connection between the rod chamber 125A and bottom chamber 125B of the fork cylinder 125 and the hydraulic oil tank 71 is cut off, allowing the fork cylinder 125 to be operated by the work operation lever 334.

[0050] Specifically, when the changeover valve 74 is switched to the float position 741 by the changeover switch 335 (on operation), it switches to the float position 741 based on the switching command from the controller 9 (the state shown in Figure 6). At this time, the indicator 61 indicates the insertion / removal permission position that allows the insertion and removal of the fork 2 from the pallet P.

[0051] As a result, the weight of the pallet including the load and the weight of the fork 2 cause the hydraulic fluid in the rod chamber 125A and bottom chamber 125B of the fork cylinder 125 to flow into the hydraulic fluid tank 71, causing the rod 125C to retract. Consequently, the fork 2 tilts forward toward the front of the vehicle without the operator having to operate the fork 2 using the work operation lever 334.

[0052] In this embodiment, if the changeover switch 335 is operated to instruct a switch to the float position 741 (on operation) when the indicator 61 does not indicate the insertion / removal permitted position, the changeover valve 74 is locked to the float position 741 by the float prohibition control of the controller 9 and maintained in the float release position 742 (the state shown in Figure 5). In this case, the fork 2 will operate as usual according to the operation of the work operation lever 334.

[0053] At this time, an alarm device 34 installed in the control unit 13 will sound an alarm, prompting the operator to be careful not to switch the switching valve 74 to the float position 741. The alarm device 34 may also audibly alert the operator using a buzzer or voice, or visually alert the operator using text or images.

[0054] This prevents the fork 2 from tilting forward without operation of the work lever 334, even if the changeover switch 335 is accidentally turned on and the float function in the fork cylinder 125 is activated, when it is undesirable to pull the fork 2 out of the pallet P, that is, when the height position of the fork 2 is not in an appropriate position relative to the insertion space of the pallet P.

[0055] Furthermore, in this embodiment, the operating unit 13 is provided with a limit switch 82 as a limiting device to restrict the float prohibition control by the controller 9. When the float prohibition control of the controller 9 is restricted by the limit switch 82 (operated to ON), even if the changeover switch 335 is operated to ON when the indicator 61 does not indicate the insertion / removal permitted position, the changeover valve 74 will switch to the float position 741 and the alarm device 34 will not activate.

[0056] For example, when performing cargo handling operations using the wheel loader 1, even in situations where it is undesirable to withdraw the forks 2 from the pallet P, the operator may still decide to withdraw the forks 2 from the pallet P. In such cases, by using the limit switch 82, it is possible to deliberately prevent the controller 9 from executing float prohibition control and to prevent the alarm device 34 from activating.

[0057] Furthermore, in this embodiment, even when the vehicle's travel speed S is greater than or equal to a predetermined speed threshold Sth (S≧Sth), the switching valve 74 is locked to the float position 741 by the float prohibition control of the controller 9 and maintained in the float release position 742 (as shown in Figure 5).

[0058] The vehicle's speed S is detected by a vehicle speed sensor 62, which acts as a vehicle speed detection device. The vehicle speed sensor 62 may be, for example, a sensor that detects the rotational speed of the wheels 11. Here, the "predetermined speed threshold Sth" is a value based on the vehicle's running state, that is, the running speed that indicates the vehicle is not stationary, and is set to, for example, about 1 km / h.

[0059] This is to reduce the risk that, when the vehicle is in motion, the fork 2 may tilt forward due to the float function without operation of the work control lever 334, and then rapidly descend downward (towards the ground) and collide with the ground or the cargo bed.

[0060] Furthermore, in this embodiment, when the switching valve 74 is switched to the float position 741, if the vehicle's reverse distance L becomes greater than or equal to a predetermined distance threshold Lth (L≧Lth), it switches from the float position 741 to the float release position 742.

[0061] The vehicle's reverse distance L is detected by a reverse distance sensor 63, which acts as a reverse distance detection device. The reverse distance sensor 63 may include, for example, a sensor that measures the distance the vehicle has moved in reverse based on the rotation speed of the wheels 11.

[0062] Here, the "predetermined distance threshold Lth" corresponds to the distance based on the reverse distance of the vehicle body when the fork 2 is completely withdrawn from the insertion space of the pallet P, and is set based on the length of the portion of the fork 2 (insertion plate portion 21A) that is inserted into the insertion space of the pallet P.

[0063] This prevents the fork 2 from tilting forward due to its float function and colliding with the ground when it is fully withdrawn from the insertion space of the pallet P.

[0064] Furthermore, in this embodiment, a relief valve 75 is provided on a relief pipeline 701B that branches off from the main pipeline 701 connecting the directional control valve 73 and the rod chamber 125A of the fork cylinder 125 and connects to the hydraulic oil tank 71 (i.e., connects the rod chamber 125A of the fork cylinder 125 and the hydraulic oil tank 71) to discharge the hydraulic oil in the rod chamber 125A to the hydraulic oil tank 71.

[0065] The relief valve 75 discharges the hydraulic fluid in the rod chamber 125A to the hydraulic fluid tank 71 when the pressure Pa in the rod chamber 125A exceeds a predetermined set pressure Path (Pa ≥ Path). The "predetermined set pressure Path" is a value that can be arbitrarily changed according to the specifications of the fork 2, and is set, for example, based on the load applied to the truck bed or truck body, which serves as a pallet storage area Y (see Figure 8), via the fork 2 by the lowering operation of the lift arm 121.

[0066] As a result, even when the wheel loader 1 is unable to activate the float function in the fork cylinder 125, the hydraulic fluid in the rod chamber 125A of the fork cylinder 125 is discharged into the hydraulic fluid tank 71, allowing the rod 125C to move freely. Therefore, the operator can horizontalize the fork 2 simply by lowering the lift arm 121. In addition, when the truck bed is a pallet storage area Y (see Figure 8), the load on the truck bed and the truck body can be reduced.

[0067] Furthermore, this relief valve 75 is in a supplementary position to the float function in the fork cylinder 125, and the fork drive system 7 does not necessarily need to be equipped with the relief valve 75.

[0068] (Controller 9 configuration) Next, the configuration of the controller 9 will be explained with reference to Figure 7A.

[0069] Figure 7A is a functional block diagram showing the functions of the controller 9 according to the first embodiment.

[0070] The controller 9 is configured with a CPU, RAM, ROM, HDD, input interface, and output interface connected to each other via a bus. Various sensors such as a vehicle speed sensor 62, a reverse distance sensor 63, and a traffic sign 61, as well as various operating devices such as a changeover switch 335 and a limit switch 82, are connected to the input interface, while a changeover valve 74 and an alarm device 34 are connected to the output interface.

[0071] In this hardware configuration, the CPU reads the control program (software) stored on a recording medium such as ROM, HDD, or optical disc, expands it onto RAM, and executes the expanded control program. The control program and hardware then work together to realize the functions of the controller 9.

[0072] In this embodiment, the configuration of the controller 9 is described as a combination of software and hardware, but it is not limited to this, and it may also be configured using an integrated circuit that realizes the functions of the control program executed on the wheel loader 1.

[0073] As shown in Figure 7A, the controller 9 includes a data acquisition unit 91, a driving state determination unit 92, a float control determination unit 93, a reverse distance determination unit 94, a storage unit 95, and a command signal output unit 96.

[0074] The data acquisition unit 91 acquires the switching signal output from the changeover switch 335, the limiting signal output from the limiting switch 82, the position signal output from the sign 61 (a signal indicating that the sign 61 is in the position where insertion and removal is permitted), the vehicle's travel speed S detected by the vehicle speed sensor 62, and the vehicle's reverse distance L detected by the reverse distance sensor 63.

[0075] The traveling state determination unit 92 determines whether or not the traveling speed S of the vehicle body acquired by the data acquisition unit 91 is equal to or higher than a predetermined speed threshold Sth, that is, whether or not the vehicle body is in a traveling state.

[0076] The float control determination unit 93 determines to execute float prohibition control for maintaining the switching valve 74 at the float release position 742 when the traveling state determination unit 92 determines that the traveling speed S of the vehicle body is equal to or higher than the predetermined speed threshold Sth (S≧Sth), that is, when it is determined that the vehicle body is in the traveling state.

[0077] Subsequently, the float control determination unit 93 determines to cancel the float prohibition control when it is determined that the traveling speed S of the vehicle body re-acquired by the data acquisition unit 91 is less than the predetermined speed threshold Sth (S<Sth), that is, when the vehicle body has stopped.

[0078] Further, the float control determination unit 93 determines to execute float control for switching the switching valve 74 to the float position 741 when the data acquisition unit 91 acquires an ON signal as a switching signal from the changeover switch 335, that is, when an operation for instructing switching to the float position 741 is performed by the changeover switch 335.

[0079] However, when the data acquisition unit 91 acquires an ON signal from the changeover switch 335 while not acquiring the position signal from the marker 61, that is, when an operation for instructing switching to the float position 741 is performed by the changeover switch 335 while the marker 61 does not indicate the insertion / removal permission position, the float control determination unit 93 determines to execute the float prohibition control.

[0080] Furthermore, if the data acquisition unit 91 has acquired an ON signal as a restriction signal from the restriction switch 82, the float control determination unit 93 will decide to execute float control even if it has acquired an ON signal from the changeover switch 335 when it has not acquired a position signal from the indicator 61. In other words, if the float control determination unit 93 has performed an operation to restrict float prohibition control by the restriction switch 82, and the indicator 61 is not indicating the insertion / removal permitted position, and an operation to switch to the float position 741 has been performed by the changeover switch 335, the float control determination unit 93 will decide to execute float control.

[0081] The reverse distance determination unit 94 determines whether the reverse distance L of the vehicle body acquired by the data acquisition unit 91 is greater than or equal to a predetermined distance threshold Lth.

[0082] The storage unit 95 is a memory that stores a predetermined speed threshold Sth and a predetermined distance threshold Lth, respectively.

[0083] When the float control determination unit 93 determines that float control should be performed, the command signal output unit 96 outputs a float command signal to the switching valve 74 to switch the switching valve 74 to the float position 741 (execution of float control by the controller 9).

[0084] On the other hand, if the float control determination unit 93 determines that float prohibition control should be performed, the command signal output unit 96 outputs a lock command signal to the switching valve 74 to lock the switching of the switching valve 74 to the float position 741 and maintain the switching valve 74 in the float release position 742 (execution of float prohibition control by the controller 9).

[0085] Furthermore, if the float control determination unit 93 determines that the float prohibition control should be released, the command signal output unit 96 outputs a lock release command signal to the switching valve 74 to release the state in which the switching valve 74 is maintained at the float release position 742 and enable the switching valve 74 to be switched to the float position 741.

[0086] Furthermore, when the indicator 61 does not indicate the insertion / removal permitted position, the command signal output unit 96 outputs an alarm command signal to the alarm device 34 if the changeover switch 335 is used to instruct the unit to switch to the float position 741, and the float control determination unit 93 decides to execute float prohibition control.

[0087] Furthermore, if the command signal output unit 96 outputs a float command signal to the switching valve 74 and then the data acquisition unit 91 acquires an off signal from the changeover switch 335, or if the reverse distance determination unit 94 determines that the reverse distance L of the vehicle body is greater than or equal to a predetermined distance threshold Lth (L≧Lth), the command signal output unit 96 outputs a float release command signal to the switching valve 74 to switch the switching valve 74 from the float position 741 to the float release position 742.

[0088] (Processing performed by controller 9 and movement of fork 2) Next, the processing flow executed by the controller 9 and the movement of the fork 2 in accordance with the control by the controller 9 will be explained with reference to Figures 7B and 8.

[0089] Figure 7B is a flowchart showing the processing flow executed by the controller 9 according to the first embodiment. Figure 8 is an explanatory diagram illustrating how the fork 2 is pulled out from the pallet P.

[0090] First, the operator presses the accelerator pedal 331A to move the vehicle forward in order to transport the pallet P loaded with cargo X to the pallet storage area Y. As shown in Figure 7B, the controller 9's data acquisition unit 91 acquires the vehicle's travel speed S (hereinafter referred to as "vehicle speed S") detected by the vehicle speed sensor 62 (S911).

[0091] Next, the driving state determination unit 92 determines whether the vehicle speed S obtained in step S911 is equal to or greater than a predetermined speed threshold Sth (S912).

[0092] When it is determined in step S912 that the vehicle speed S is equal to or higher than a predetermined speed threshold Sth (S≧Sth) (S912 / YES), that is, when the vehicle body starts moving and enters a traveling state, the command signal output unit 96 outputs a lock command signal to the switching valve 74 (S913). On the other hand, when it is determined in step S912 that the vehicle speed S is less than the predetermined speed threshold Sth (S<Sth) (S912 / NO), the process returns to step S911.

[0093] Next, the data acquisition unit 91 acquires the vehicle speed S detected by the vehicle speed sensor 62 again (S914). Subsequently, the traveling state determination unit 92 determines whether or not the vehicle speed S re-acquired in step S914 is less than the predetermined speed threshold Sth (S915).

[0094] When it is determined in step S915 that the vehicle speed S is less than the predetermined speed threshold Sth (S<Sth) (S915 / YES), that is, when the vehicle body arrives at the pallet storage site Y (the state shown at the upper left end in FIG. 8), the command signal output unit 96 outputs an unlock command signal to the switching valve 74 (S916). On the other hand, when it is determined in step S915 that the vehicle speed S is equal to or higher than the predetermined speed threshold Sth (S≧Sth) (S915 / NO), the process returns to step S914.

[0095] Next, as in the state shown in the upper center in FIG. 8, the operator operates the work operation lever 334 to lower the lift arm 121. Subsequently, the operator checks whether or not the indicator 61 indicates the insertion / extraction permitted position. When the operator determines that the indicator 61 indicates the insertion / extraction permitted position, the operator turns on the changeover switch 335.

[0096] At this time, in the controller 9, as shown in FIG. 7B, the data acquisition unit 91 acquires the ON signal from the changeover switch 335 (S917 / YES) and also acquires the position signal from the indicator 61 (S918 / YES), so that the command signal output unit 96 outputs a float command signal to the switching valve 74 (S919).

[0097] As a result, the switching valve 74 switches to the float position 741, and the fork 2 tilts forward as shown in the upper right corner of Figure 8.

[0098] Next, as shown in the lower left of Figure 8, the operator starts reversing the vehicle to pull the fork 2 out of the insertion space of the pallet P. At this time, the operator turns off the changeover switch 335 to disable the float function of the fork cylinder 125. Then, as shown in the lower right of Figure 8, the operator continues to reverse the vehicle, and when the entire insertion plate portion 21A of the fork 2 is pulled out of the insertion space of the pallet P, the removal of the fork 2 is completed.

[0099] At this point, as shown in Figure 7B, the controller 9's data acquisition unit 91 acquires an off signal from the changeover switch 335 (S920 / YES). Then, the command signal output unit 96 outputs a float release command signal to the changeover valve 74 (S923), and the processing in the controller 9 is completed.

[0100] On the other hand, if the operator does not turn off the changeover switch 335 when the vehicle starts to reverse, that is, if the data acquisition unit 91 does not receive an off signal from the changeover switch 335 (S920 / NO), the data acquisition unit 91 acquires the reverse distance L detected by the reverse distance sensor 63 (S921).

[0101] Next, the reverse distance determination unit 94 determines whether the reverse distance L obtained in step S921 is greater than or equal to a predetermined distance threshold Lth (S922).

[0102] If it is determined in step S922 that the reverse distance L is greater than or equal to a predetermined distance threshold Lth (L≧Lth) (S922 / YES), the command signal output unit 96 outputs a float release command signal to the switching valve 74 (S923), and the processing in the controller 9 ends.

[0103] As a result, the switching valve 74 is switched from the float position 741 to the float release position 742, enabling operation of the fork 2 via the work operation lever 334. Even in this case, the operator continues to reverse the vehicle body, and when the entire insertion plate portion 21A of the fork 2 is pulled out from the insertion space of the pallet P, the pulling-out of the fork 2 is completed.

[0104] On the other hand, when it is determined in step S922 that the reverse travel distance L is less than the predetermined distance threshold Lth (L<Lth) (S922 / NO), the process returns to step S920.

[0105] Here, when the data acquisition unit 91 has acquired the ON signal from the changeover switch 335 (S917 / YES) but has not acquired the position signal from the marker 61 (S918 / NO), the controller 9 determines whether the data acquisition unit 91 has acquired a signal from the restriction switch 82 (S924).

[0106] When it is determined in step S924 that the data acquisition unit 91 has acquired the OFF signal from the restriction switch 82 (S924 / YES), that is, when no operation for restricting the float prohibition control has been performed by the restriction switch 82, the command signal output unit 96 outputs a lock command signal to the switching valve 74 and outputs an alarm command signal to the alarm device 34 (S925), then returns to step S917.

[0107] Meanwhile, when it is determined in step S924 that the data acquisition unit 91 has acquired the ON signal from the restriction switch 82 (S924 / NO), that is, in a state where an operation for restricting the float prohibition control has been performed by the restriction switch 82, the process proceeds to step 919, and the command signal output unit 96 outputs a float command signal to the switching valve 74.

[0108] In this way, by providing the fork cylinder 125 with a float function, the pulling-out operation of the fork 2 from the pallet on which the load is placed can be performed smoothly without being affected by the environment of the work site.

[0109] In this embodiment, the controller 9 performed float control when the operator determined that the position of the indicator 61 was the insertion / removal permitted position and then turned on the changeover switch 335. However, the controller 9 is not limited to this, and may also perform float control when it receives a position signal from the indicator 61 and an ON signal from the changeover switch 335.

[0110] <Second Embodiment> Next, a wheel loader 1 according to the second embodiment of the present invention will be described with reference to Figures 9 to 12. In Figures 9 to 12, components that are common to those described in the first embodiment are denoted by the same reference numerals and their descriptions are omitted.

[0111] In this embodiment, the float function is automatically activated by the controller 9, without the operator having to operate the changeover switch 335.

[0112] Figure 9 is a partially enlarged perspective view showing one example configuration of a work device 12 according to the second embodiment of the present invention. Figure 10 is a system configuration diagram showing one example configuration of a fork drive system 7A according to the second embodiment of the present invention.

[0113] In the fork drive system 7A according to this embodiment, a position sensor 61A, which is a position detection device for detecting the position information of the fork 2 in the height direction, is used as a switching indicator device. The position sensor 61A is, for example, an infrared sensor, which is electrically connected to the controller 9A and outputs the detected position information to the controller 9A.

[0114] In Figure 9, the position sensor 61A is attached to the central part of the lower side of the connection portion 22 of the fork 2. However, there are no particular restrictions on the mounting location of the position sensor 61A; any mounting location that can detect the height position of the fork 2 is acceptable.

[0115] In this embodiment, the control of the switching valve 74 by the controller 9A is selected by a selection switch 84 provided in the operating unit 13 (see Figure 1). In other words, the selection switch 84 is a selection device for selecting whether to enable or disable the control of the switching valve 74 by the controller 9A.

[0116] When the operator turns on the selection switch 84, and the controller 9A is selected to enable control of the switching valve 74, the selection switch 84 outputs an ON signal to the controller 9A. As a result, the controller 9A starts the control process related to the switching valve 74.

[0117] Next, the functional configuration of controller 9A will be explained with reference to Figure 11. Figure 11 is a functional block diagram showing the functions of controller 9A.

[0118] The controller 9A includes a data acquisition unit 91A, a position determination unit 97, a reverse distance determination unit 94, a storage unit 95A, and a command signal output unit 96.

[0119] The data acquisition unit 91A acquires the ON signal output from the selection switch 84, the position information of the fork 2 detected by the position sensor 64, and the reverse distance L of the vehicle body detected by the reverse distance sensor 63.

[0120] The position determination unit 97 determines whether the position information of the fork 2 acquired by the data acquisition unit 91 indicates a position where insertion and removal is permitted.

[0121] The reverse distance determination unit 94 determines whether the reverse distance L of the vehicle body acquired by the data acquisition unit 91A is equal to or greater than a predetermined distance threshold Lth.

[0122] The storage unit 95A is a memory that stores data relating to a predetermined height indicating the insertion / removal permitted position and a predetermined distance threshold Lth, respectively.

[0123] The command signal output unit 96 outputs a float command signal to the switching valve 74 to switch the switching valve 74 to the float position 741 when an ON signal is acquired by the data acquisition unit 91 (i.e., the control of the switching valve 74 by the controller 9A is selected by the selection switch 84) and the position determination unit 97 determines that the position information of the fork 2 indicates the insertion / removal permitted position (it is below a predetermined height).

[0124] Furthermore, after outputting a float command signal to the switching valve 74, if the reverse distance determination unit 94 determines that the vehicle's reverse distance L is greater than or equal to a predetermined distance threshold Lth (L≧Lth), the command signal output unit 96 outputs a float release command signal to the switching valve 74 to switch the switching valve 74 to the float release position 742.

[0125] Next, the processing flow executed within controller 9A will be explained with reference to Figure 12. Figure 12 is a flowchart showing the processing flow executed in controller 9A.

[0126] In controller 9A, first, it is determined whether the data acquisition unit 91 has acquired an ON signal from the selection switch 84, that is, whether the selection switch 84 has been operated to the ON position (S901).

[0127] If the data acquisition unit 91 determines in step S901 that it has received an ON signal from the selection switch 84 (S901 / YES), the data acquisition unit 91 acquires the position information of the fork 2 detected by the position sensor 64 (S902).

[0128] If, in step S901, it is determined that the data acquisition unit 91 has not acquired an ON signal from the selection switch 84 (step S901 / NO), the controller 9A will not proceed to the next step until the data acquisition unit 91 acquires an ON signal from the selection switch 84, that is, until the selection switch 84 is turned ON.

[0129] Next, the position determination unit 97 determines whether or not the position information of the fork 2 acquired in step S902 indicates the insertion / removal permitted position (S903).

[0130] When it is determined in step S903 that the position information of the fork 2 indicates the insertion / removal permitted position (S903 / YES), that is, when the position information is less than a predetermined height, the command signal output unit 96 outputs a float command signal to the switching valve 74 (S904).

[0131] On the other hand, when it is determined in step S903 that the position information of the fork 2 does not indicate the insertion / removal permitted position (S903 / NO), that is, when the position information is equal to or greater than the predetermined height, the process returns to step S902, and does not proceed to the next processing until the position information of the fork 2 indicates the insertion / removal permitted position.

[0132] Next, the data acquisition unit 91 acquires the reverse travel distance L of the vehicle body detected by the reverse travel distance sensor 63 (S905).

[0133] Subsequently, the reverse travel distance determination unit 94 determines whether or not the reverse travel distance L of the vehicle body acquired in step S905 is equal to or greater than a predetermined distance threshold Lth (S906).

[0134] When it is determined in step S906 that the reverse travel distance L of the vehicle body is equal to or greater than the predetermined distance threshold Lth (L≧Lth) (S906 / YES), the command signal output unit 96 outputs a float release command signal to the switching valve 74 (S907), and the processing in the controller 9A ends.

[0135] On the other hand, when it is determined in step S906 that the reverse travel distance L of the vehicle body is less than the predetermined distance threshold Lth (L<Lth) (S906 / NO), the process returns to step S905, and does not proceed to the next processing until the reverse travel distance L of the vehicle body becomes equal to or greater than the predetermined distance threshold Lth.

[0136] Thus, in this embodiment as well, by activating the float function in the fork cylinder 125 with the controller 9A, it becomes possible to smoothly pull out the forks 2 from the pallet on which the load is placed, regardless of the environment of the work site.

[0137] The embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the embodiments described above, and various modifications are included. For example, in the above embodiments, a wheel loader 1 with pallet forks was described as an example of a work vehicle, but the invention is not limited to this, and other work vehicles such as tractors may be used as long as they are equipped with forks 2.

[0138] Furthermore, in the first embodiment described above, the controller 9 performed float control based on an output signal from the indicator 61 or the like, in addition to the ON signal from the changeover switch 335. However, it is not limited to this, and float control may be performed based solely on the ON signal from the changeover switch 335. In other words, the controller 9 may not be connected to the indicator 61 or the like, and may be configured to output a float command signal or a float release command signal based solely on the operation of the changeover switch 335 by an operator who has confirmed the status of the indicator 61. [Explanation of Symbols]

[0139] 1: Wheel loader (work vehicle) 1A: Front frame (body) 1B: Rear frame (body) 2: Fork 9,9A: Controller 13: Driver's Unit 34:Alarm device 61:Sign 61A: Position sensor (position detection device) 62: Vehicle speed sensor (vehicle speed detection device) 63: Reverse distance sensor (reverse distance detection device) 71: Hydraulic oil tank 74: Switching valve 75: Relief valve 82: Limiting switch (limiting device) 84: Selection switch (selection device) 121: Lift arm (arm component) 123: Backrest 125: Fork Cylinder (Attachment Hydraulic Cylinder) 125A: Rod chamber 125B: Bottom Chamber 211: Top surface 212: Bottom 334: Operation lever (operation lever) 335: Changeover switch (manual operating device) 701B: Relief conduit 741: Float position 742: Float release position L: Backward distance Lth: Distance threshold P: Palette S: Traveling speed Sth: Velocity threshold Z: ground plane

Claims

1. The car body and, An arm member attached to the front of the vehicle body, A fork is attached to the tip of the aforementioned arm member via a backrest, An attachment hydraulic cylinder that rotates the fork vertically relative to the tip of the arm member, An operating lever for operating the aforementioned attachment hydraulic cylinder, In a work vehicle equipped with, A switching valve that can be switched between a float position that connects the rod chamber and bottom chamber of the attachment hydraulic cylinder to the hydraulic fluid tank, and a float release position that blocks communication between the rod chamber and bottom chamber of the attachment hydraulic cylinder and the hydraulic fluid tank, thereby enabling operation of the attachment hydraulic cylinder by the operating lever. A controller that controls the aforementioned switching valve, Equipped with A work vehicle characterized by the following features.

2. In the work vehicle described in claim 1, The driver's compartment where the operator sits, A marker is provided that protrudes from one side of the backrest in the vehicle width direction and indicates the position of the fork in the height direction relative to the ground surface, A manual operating device provided in the operating unit for operating the switching of the switching valve to the float position, Equipped with, The aforementioned controller, When the manual operating device is used to instruct the switching to the float position, the switching valve is switched to the float position. A work vehicle characterized by the following features.

3. In the work vehicle described in claim 2, Furthermore, equipped with an alarm system, The aforementioned controller, If the sign does not indicate the insertion / removal permitted position for inserting and removing the forks from the pallet for cargo transport, and the manual control device is used to instruct the user to switch to the float position, the alarm device will sound an alarm and the float-prohibition control will be executed to maintain the switching valve in the float-release position. A work vehicle characterized by the following features.

4. In the work vehicle described in claim 3, The operating unit is further provided with a limiting device for limiting the float prohibition control, The aforementioned controller, If the float prohibition control is restricted by the limiting device, and the indicator does not indicate the removal permission position, and the manual operating device is used to instruct the switching to the float position, the float prohibition control will not be executed, and the switching valve will be switched to the float position. A work vehicle characterized by the following features.

5. In the work vehicle described in claim 1, The vehicle further includes a vehicle speed detection device that detects the vehicle's travel speed. The aforementioned controller, If the vehicle speed detected by the vehicle speed detection device is equal to or greater than a predetermined speed threshold, float prohibition control is executed to maintain the switching valve in the float release position. A work vehicle characterized by the following features.

6. In the work vehicle described in claim 1, The vehicle further includes a reverse distance detection device for detecting the reverse distance of the vehicle body, The aforementioned controller, When the switching valve is switched to the float position and the reverse distance detected by the reverse distance detection device exceeds a predetermined distance threshold, the switching valve is switched from the float position to the float release position. A work vehicle characterized by the following features.

7. In the work vehicle described in claim 1, A selection device for selecting whether to enable or disable the control of the switching valve by the controller, A position detection device that detects the positional information of the fork in the height direction relative to the ground surface, Equipped with, The aforementioned controller, When the selection device selects that the controller control of the switching valve is enabled, and the position information detected by the position detection device is less than a predetermined height, the switching valve is switched to the float position. A work vehicle characterized by the following features.

8. In the work vehicle described in claim 1, The attachment hydraulic cylinder is further provided with a relief valve located on the relief pipeline connecting the rod chamber and the hydraulic fluid tank, which discharges the hydraulic fluid from the rod chamber to the hydraulic fluid tank when the pressure in the rod chamber exceeds a predetermined set pressure. A work vehicle characterized by the following features.

9. In the work vehicle described in claim 1, The tip of the aforementioned fork is, The bottom surface, opposite to the top surface on which the load is placed, is formed in an arc shape that curves downwards. A work vehicle characterized by the following features.

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