Forklift loading equipment

Abstract

To provide a forklift cargo handling gear which can realize a shockless full-free cylinder and prevent an operation of a lift cylinder during rising of the full-free cylinder.SOLUTION: In the forklift cargo handling gear, a full-free cylinder 37 includes a cylinder body 38, a slidable piston 39, a piston rod 40 connected to the piston 39, a full-free cylinder hydraulic oil chamber to which hydraulic oil is supplied through a first hydraulic oil path, a cylinder space 43 that stores shockless hydraulic oil, a rod space 44 formed in the piston rod 40, in communication with the cylinder space through a diaphragm path 45, a switching valve 62 that switches distribution of hydraulic oil to a second hydraulic oil path, a pressure sensor 64 that detects the pressure of the first hydraulic oil path, and a controller 61 that controls opening / closing of the switching valve 62. The controller 61 opens the switching valve 62 when the pressure sensor 64 detects pressure exceeding a preset threshold value.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a cargo handling device for a forklift. [Background technology]

[0002] Some forklifts are equipped with a full-free type cargo handling device, which has a pair of left and right lift cylinders and a full-free cylinder. The lift cylinders are hydraulic cylinders that raise and lower the inner masts, and the full-free cylinders are hydraulic cylinders that raise and lower the lift brackets equipped with forks relative to the inner masts (see, for example, Patent Document 1).

[0003] This type of cargo handling device has a control valve that supplies and discharges hydraulic oil to the lift cylinder and full free cylinder, a hydraulic pipe that connects the control valve to the full free cylinder, and a hydraulic pipe that branches off from the hydraulic pipe and connects to the lift cylinder. When the inner mast and forks are raised from their lowest positions, the full free cylinder rises and the rod of the full free cylinder fully extends before the lift cylinder begins to extend. When the rod of the full free cylinder fully extends and the piston of the full free cylinder hits the rod guide, a shock occurs. However, Patent Document 1 employs a shockless mechanism to alleviate this shock.

[0004] When the fork is raised, hydraulic oil is supplied to the full free cylinder, causing the piston to rise. As the piston approaches the cylinder rod guide, the cylinder rod guide abuts against the hydraulic oil. As the piston rises, the hydraulic oil in the cavity is compressed between the rod guide and the piston. The compressed hydraulic oil then moves through the communication passage toward the reservoir and the rod chamber. During this movement, the hydraulic oil is throttled by the throttle portion of the communication passage, creating a certain resistance force on the piston. This resistance slows the piston's operating speed, causing its relative position to change relative to the rod guide. Therefore, the hydraulic oil being throttled by the throttle portion of the communication passage reduces shock at the end of the extension stroke of the cylinder rod. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-3199 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in Patent Document 1, the hydraulic oil in the space is compressed between the rod guide and the piston, so if the amount of hydraulic oil in the space increases, there is a problem that the lift cylinder rises when the piston of the full free cylinder does not rise sufficiently.

[0007] The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a loading and unloading device for a forklift that realizes shockless full free cylinders and prevents the lift cylinder from operating when the full free cylinder is raised. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a shipbuilding system comprising: outer masts; inner masts that can be raised and lowered relative to the outer masts; lift brackets that can be raised and lowered relative to the inner masts; a full free cylinder that raises and lowers the lift brackets relative to the inner masts; and a lift cylinder that raises and lowers the inner masts relative to the outer masts. A hydraulic oil tank that stores hydraulic oil for the lift cylinder; Hydraulic oil From the hydraulic oil tank a hydraulic oil pump that pumps up hydraulic oil; a lift lever that operates to raise and lower the lift bracket; and a control valve that controls the supply and discharge of hydraulic oil to the full free cylinder and the lift cylinder in conjunction with the operation of the lift lever. The control valve and the full free cylinder are connected, and the a first hydraulic oil passage for passing hydraulic oil to the full free cylinder; and connected to the lift cylinder , From the first hydraulic oil passage a second hydraulic oil passage for passing hydraulic oil to the lift cylinder; The control valve is disposed closer to the hydraulic oil tank than the branching portion of the first hydraulic oil passage to the second hydraulic oil passage. In a loading and unloading device of a forklift truck, the full free cylinder comprises a cylinder body, a piston slidable up and down inside the cylinder body, a piston rod connected to the piston and extending and retracting relative to the cylinder body, a full free cylinder hydraulic oil chamber formed below the piston in the cylinder body and to which hydraulic oil is supplied via the first hydraulic oil passage, a cylinder space formed above the piston in the cylinder body between the piston rod and the cylinder body and storing shockless hydraulic oil to prevent shock when the piston stops rising, a rod space formed inside the piston rod, and a throttle passage formed in the piston rod that communicates the rod space with the cylinder space, provided in the second hydraulic oil passage, The flow and cut-off of hydraulic oil to the second hydraulic oil passage is switched by opening and closing the passage. When hydraulic oil is supplied to the full free cylinder by the control valve, the supply of hydraulic oil to the lift cylinder is cut off by closing the valve, and hydraulic oil can be supplied to the lift cylinder by opening the valve. a pressure sensor for detecting the pressure of the first hydraulic oil passage; and a controller for controlling the opening and closing of the switching valve, When the switching valve is in a closed state, the control valve supplies hydraulic oil to the full free cylinder. The switching valve is opened when the pressure sensor detects a pressure exceeding a preset threshold value.

[0009] In this invention, when the lift bracket is raised, the control valve supplies hydraulic oil to the full free cylinder hydraulic oil chamber through the first hydraulic oil passage so as to extend the full free cylinder. Before the full free cylinder is almost completely extended, the hydraulic oil pressure in the cylinder space increases, causing hydraulic oil to flow from the cylinder space to the rod space through the throttle passage, thereby mitigating shock. When the pressure in the first hydraulic oil passage exceeds a threshold, the switching valve switches from a closed state to an open state, allowing hydraulic oil to be supplied to the lift cylinder. Therefore, even if the full free cylinder is extended with an increased amount of hydraulic oil in the cylinder chamber, the lift cylinder will not extend before the full free cylinder is almost completely extended. As a result, the full free cylinder is shockless and the lift cylinder can be prevented from operating at any time other than when the full free cylinder is about to stop rising.

[0010] In addition, in the loading device of the forklift ,before The lever sensor detects the operating position of the lift lever. Sa When the switching valve is in an open state and the lift lever is in a raised position, the controller The switching valve is not closed even when the pressure in the first hydraulic oil passage becomes equal to or lower than a threshold value. This may also be configured as follows. In this case, when the full free cylinder is fully extended and the lift cylinder is extended, the switching valve is in an open state. When the switching valve is in an open state and the lift lever is in the raised position, the pressure in the first hydraulic oil passage is lower than the threshold value. below Even if the valve is open, the switching valve remains open, so that the supply of hydraulic oil to the lift cylinder can be continued, allowing the lift cylinder to be lifted stably. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a cargo handling device for a forklift that can realize a shockless full free cylinder and prevent the lift cylinder from operating when the full free cylinder is raised. [Brief explanation of the drawings]

[0012] [Figure 1]1 is a side view of a forklift according to an embodiment of the present invention. [Figure 2] 1 is a front perspective view of a cargo handling device of a forklift according to an embodiment of the present invention, as viewed obliquely from the front. [Figure 3] 1 is an explanatory diagram schematically illustrating a cargo handling apparatus according to the present invention. [Figure 4] FIG. 2 is an explanatory diagram illustrating a hydraulic circuit of the cargo handling apparatus of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] A loading and unloading device for a forklift according to an embodiment of the present invention will be described below with reference to the drawings. The loading and unloading device for a forklift according to this embodiment is an example applied to a forklift with a three-stage full free mast. Note that the terms "front and back," "left and right," and "up and down" that specify directions are shown based on the state in which the forklift operator is seated in the driver's seat and facing the forward direction of the forklift.

[0014] As shown in Figure 1, the forklift 10 is provided with a cargo handling device 12 at the front of a vehicle body 11. A driver's seat 13 is provided near the center of the vehicle body 11. Drive wheels 14 are provided as front wheels at the front of the vehicle body 11, and steering wheels 15 are provided as rear wheels at the rear of the vehicle body 11. A counterweight 16 is provided at the rear of the vehicle body 11, and the counterweight 16 is used to adjust the vehicle weight and achieve weight balance in the vehicle body 11. The forklift 10 of this embodiment is an engine forklift.

[0015] The vehicle body 11 is provided with a head guard 17 that covers the upper part of the driver's seat 13. A tilt cylinder 18 that is operated by hydraulic oil is installed between the vehicle body 11 and the cargo handling device 12. Operation of the tilt cylinder 18 causes the cargo handling device 12 to tilt in the front-to-rear direction with the lower end of the cargo handling device 12 as a fulcrum.

[0016] As shown in Figure 2, the cargo handling apparatus 12 is equipped with a mast 22 having outer masts 19, middle masts 20, and inner masts 21. The pair of left and right outer masts 19 are equipped with a pair of left and right middle masts 20 that can be raised and lowered inside the outer masts 19. The middle masts 20 are equipped with inner masts 21 that can be raised and lowered inside the middle masts 20. The cargo handling apparatus 12 is equipped with lift brackets 23 that rise and fall along the inner masts 21, and the lift brackets 23 allow various attachments to be attached and detached.

[0017] The upper ends of the outer masts 19 are connected by an upper beam 24. The lower parts of the outer masts 19 are connected by a lower beam (not shown). The upper ends of the middle masts 20 are connected by an upper beam 25. The lower parts of the middle masts 20 are connected by a bottom beam (not shown). The upper ends of the inner masts 21 are connected by an upper beam 26. The lower parts of the inner masts 21 are connected by a lower beam 27. As shown in Figure 2, the lift bracket 23 is provided with a pair of left and right forks 28 and a backrest 29. The left and right forks 28 scoop up and support a load. The backrest 29 supports the rear of the load supported by the pair of left and right forks 28.

[0018] As shown in Figure 3, one end of a lift chain 30 is fixed to the upper part of the outer mast 19. A chain wheel 31, around which the lift chain 30 is looped, is provided at the upper part of the middle mast 20, and the lift chain 30 is looped around the chain wheel 31, with the other end of the lift chain 30 fixed to the lower part of the inner mast 21. The outer mast 19 is provided with a lift cylinder 32 that is operated by the supply and discharge of hydraulic oil. By operating the lift cylinder 32, the middle mast 20 rises and falls inside the outer mast 19, and the inner mast 21 rises and falls inside the middle mast 20.

[0019] As shown in Figure 3, the lift cylinder 32 includes a cylinder body 33, a piston 34 that slides inside the cylinder body 33, and a piston rod 35 that is connected to the piston 34 and extends and retracts relative to the cylinder body 33. A hydraulic oil chamber 36 is formed in the cylinder body 33 below the piston 34, serving as a lift cylinder hydraulic oil chamber. When hydraulic oil is supplied to the hydraulic oil chamber 36, the piston 34 rises in the cylinder body 33 and the piston rod 35 extends. When hydraulic oil is discharged from the hydraulic oil chamber 36, the piston 34 descends in the cylinder body 33 and the piston rod 35 retracts. The upper end of the piston rod 35 is connected to the upper beam 25 of the middle mast 20.

[0020] As shown in Figure 3, a full free cylinder 37 is erected on the lower beam 27 of the inner mast 21. The full free cylinder 37 is a hydraulic cylinder for raising and lowering the lift bracket 23 relative to the inner mast 21. As shown in Figure 4, the full free cylinder 37 includes a cylinder body 38, a piston 39 that slides inside the cylinder body 38, and a piston rod 40 that is connected to the piston 39 and extends and retracts relative to the cylinder body 38. A hydraulic oil chamber 41 is formed in the cylinder body 38 below the piston 39, serving as a full free cylinder hydraulic oil chamber. When hydraulic oil is discharged from the hydraulic oil chamber 41, the piston 39 descends the cylinder body 38 and the piston rod 40 retracts. The pressure-receiving area of ​​the hydraulic oil chamber 41 is set smaller than that of the hydraulic oil chamber 36 of the lift cylinder 32.

[0021] As shown in FIG. 4, the full free cylinder 37 is equipped with a shockless mechanism 42 that prevents shock when the piston 39 stops rising. Above the piston 39 in the cylinder body 38, a cylinder space 43 is formed between the piston rod 40 and the cylinder body 38. A certain amount of hydraulic oil for shockless operation is stored in the cylinder space 43. The piston rod 40 is provided with a rod space 44 and a throttle passage 45 that connects the cylinder space 43 to the rod space 44. In other words, the shockless mechanism 42 has the cylinder space 43, the rod space 44, and the throttle passage 45. A communication passage 48 equipped with a check valve 49 is formed between the rod space 44 and the hydraulic oil chamber 41. Therefore, when the pressure of the hydraulic oil in the rod space 44 reaches or exceeds a certain pressure, the hydraulic oil is returned from the rod space 44 to the hydraulic oil chamber 41.

[0022] When the piston rod 40 of the full free cylinder 37 rises, the hydraulic oil in the cylinder space 43 is pressurized by the piston 39 before it reaches its full rise. As a result, the hydraulic oil flows through the throttle passage 45 to the rod space 44. Because the hydraulic oil flowing through the throttle passage 45 is throttled, the ascending speed of the piston 39 decreases, and the impact when the piston 39 stops ascending is alleviated. Note that when the hydraulic oil in the cylinder space 43 flows through the throttle passage 45 to the rod space 44, the holding pressure of the full free cylinder 37 is the sum of the load pressure received by the full free cylinder 37 and the pressure loss caused by flowing through the throttle passage 45. The load pressure is based on the weight of the lift bracket 23 equipped with the forks 28, and if the forks 28 are supporting a load, the weight of the load is also added, increasing the load pressure.

[0023] As shown in Figure 2, a pair of left and right chain wheels 46 are provided on the upper end of the piston rod 40. A lift chain 47 is hung on the chain wheels 46, connecting the inner mast 21 and the lift bracket 23. One end of the lift chain 47 is connected to the upper part of the cylinder body 38, and the other end of the lift chain 47 is connected to the lower part of the lift bracket 23. Therefore, when the piston rod 40 of the full free cylinder 37 rises, the lift bracket 23 rises without the inner mast 21 and middle mast 20 rising.

[0024] Next, the hydraulic circuit 50 of the cargo handling device 12 will be described. As shown in FIG. 4, the hydraulic circuit 50 includes a hydraulic oil tank 51 that stores hydraulic oil, a hydraulic oil pump 52 that pumps hydraulic oil from the hydraulic oil tank 51, and a control valve 53 that distributes the hydraulic oil pumped by the hydraulic oil pump 52. A first pipe 54 connects the hydraulic oil tank 51 and the hydraulic oil pump 52, and a second pipe 55 connects the hydraulic oil pump 52 and the control valve 53. A third pipe 56 connects the control valve 53 and the hydraulic oil chamber 41 of the full free cylinder 37. A fourth pipe 57 branches off from the third pipe 56 and serves as a second hydraulic oil passage connected to the hydraulic oil chambers 36 of the pair of left and right lift cylinders 32. A fifth pipe 58 is also provided to return hydraulic oil from the control valve 53 to the hydraulic oil tank 51.

[0025] The control valve 53 is a mechanical control valve that is switched in conjunction with the operation of a lift lever 59 that controls the elevation of the lift bracket 23, and supplies and discharges hydraulic oil to and from the lift cylinder 32 and full free cylinder 37. The lift lever 59 is provided on the driver's seat 13, and is placed in the raised position when tilted backward and in the lowered position when tilted forward. An intermediate position is set between the raised and lowered positions of the lift lever 59, and the lift bracket 23 is not raised or lowered at the intermediate position. A lever sensor 60 is provided to detect the operating position of the lift lever 59. The lever sensor 60 is connected to a controller 61.

[0026] The controller 61 controls each part of the forklift 10 and includes a CPU and a memory unit (not shown) including RAM and the like. The controller 61 may also include dedicated hardware, such as an application-specific integrated circuit (ASIC), that performs at least some of the various processes. The controller 61 may be configured as a circuit including one or more processors operating according to a computer program, one or more dedicated hardware circuits such as ASICs, or a combination thereof. The memory unit stores program code or instructions configured to cause the CPU to execute processes. The memory unit stores various programs for controlling the forklift 10. The memory unit, i.e., computer-readable medium, includes anything accessible by a general-purpose or special-purpose computer.

[0027] In this embodiment, a switching valve 62 is provided in the fourth pipe 57. The switching valve 62 has a solenoid spool (not shown), and when the solenoid is energized, it opens so that hydraulic oil in the fourth pipe 57 can be supplied to the lift cylinder 32, and when the solenoid is deenergized, it closes. In other words, the switching valve 62 switches between opening and closing to allow or block the flow of hydraulic oil to the fourth pipe 57 as the second hydraulic oil path. In the closed position, a check valve 63 is positioned, allowing hydraulic oil from the lift cylinder 32 to the control valve 53 to pass through the switching valve 62. The switching between opening and closing of the switching valve 62 is performed by a controller 61. When not energized, the switching valve 62 is normally in the closed position.

[0028] The third pipe 56 is provided with a pressure sensor 64 that detects the oil pressure of the third pipe 56. The pressure sensor 64 is connected to the controller 61, and the oil pressure detected by the pressure sensor 64 is transmitted to the controller 61. When the switching valve 62 is in the closed state, the oil pressure detected by the pressure sensor 64 is proportional to the load that the full free cylinder 37 receives from the lift bracket 23.

[0029] In this embodiment, a certain amount of hydraulic oil for shockless operation is stored in the cylinder space 43 of the full free cylinder 37. The controller 61 controls the switching valve 62 to prevent the lift cylinder 32 from starting to extend while the full free cylinder 37 is still extending. The controller 61 has a preset hydraulic pressure threshold for the third pipe 56. The threshold is set based on the holding pressure of the full free cylinder 37 when the piston 39 pressurizes the hydraulic oil in the cylinder space 43. The holding pressure of the full free cylinder 37 is the sum of the load pressure received by the full free cylinder 37 and the pressure loss caused by the hydraulic oil flowing through the throttle passage 45. Therefore, the threshold is a pressure that at least exceeds the load pressure of the full free cylinder 37.

[0030] When the detection value of the pressure sensor 64 exceeds the threshold value, it means that the piston 39 is pressurizing the hydraulic oil in the cylinder space 43, the holding pressure is increasing, and the lift of the piston 39 is nearing completion. When the lift bracket 23 is being lifted, the controller 61 controls the switching valve 62 so that the switching valve 62 is switched from the closed position to the open position when the detection value of the pressure sensor 64 exceeds the threshold value.

[0031] When the switching valve 62 is switched to the open position due to the threshold being exceeded, the controller 61 controls the switching valve 62 to maintain the open state even if the detection value of the pressure sensor 64 becomes equal to or less than the threshold when the lever sensor 60 indicates the lift lever 59 is in the raised position. By controlling the switching valve 62 to maintain the open state, the supply of hydraulic oil to the lift cylinder 32 is prevented even if the pressure fluctuation of the full free cylinder 37 occurs due to the start of hydraulic oil flow into the lift cylinder 32. but On the other hand, when the lever sensor 60 indicates that the lift lever 59 is in a position other than the raised position, the controller 61 controls the switching valve 62 to close when the detection value of the pressure sensor 64 falls below the threshold value.

[0032] Next, the operation of the cargo handling apparatus 12 of this embodiment will be described. A case where the forks 28 are raised from the lowest position to the highest position will be described. To raise the forks 28, the operator of the forklift 10 switches the lift lever 59 to the raised position. Switching the lift lever 59 to the raised position enables the control valve 53 to supply hydraulic oil to the full free cylinder 37. In addition, the controller 61 operates the hydraulic oil pump 52. At this time, the switching valve 62 is in a closed state.

[0033] When the operator operates the lift lever 59, hydraulic oil pumped up by the hydraulic oil pump 52 is supplied to the hydraulic oil chamber 41 of the full free cylinder 37 through the control valve 53. The supply of hydraulic oil to the hydraulic oil chamber 41 causes the piston 39 to rise and the piston rod 40 to extend. As the piston rod 40 extends, the lift bracket 23 equipped with the fork 28 rises relative to the inner mast 21. At this time, the holding pressure of the full free cylinder 37 is the load pressure caused by the weight of the lift bracket 23, fork 28, and backrest 29, and if the fork 28 is supporting a load, the weight of the load is added. The holding pressure of the full free cylinder 37 is determined based on the hydraulic pressure in the third pipe 56 detected by the pressure sensor 64.

[0034] When the piston 39 rises and approaches the top of the cylinder body 38, the hydraulic oil in the cylinder space 43 is pressurized by the piston 39. The hydraulic oil in the cylinder space 43 is pressurized by the piston 39 and flows through the throttle passage 45 into the rod space 44. The pressure loss caused by the hydraulic oil passing through the throttle passage 45 reduces the upward speed of the piston 39. Therefore, even when the piston 39 abuts against the cylinder body 38 and stops rising, the impact is mitigated. Meanwhile, as the hydraulic oil in the cylinder space 43 is pressurized by the piston 39, the hydraulic oil passes through the throttle passage 45 and the holding pressure of the full free cylinder 37 increases.

[0035] As the piston 39 continues to pressurize the hydraulic oil in the cylinder space 43, the holding pressure of the full free cylinder 37 exceeds the threshold value. When the holding pressure of the full free cylinder 37 exceeds the threshold value, the controller 61 switches the switching valve 62 from a closed state to an open state. At this time, the fork 28 is positioned close to the uppermost position relative to the inner mast 21. By switching the switching valve 62 to an open state, hydraulic oil from the control valve 53 is supplied to the hydraulic oil chamber 36 of the lift cylinder 32, causing the piston 34 of the lift cylinder 32 to rise and the piston rod 35 to extend. As the piston rod 35 extends, the middle mast 20 rises relative to the outer mast 19, and as the middle mast 20 rises, the inner mast 21 rises relative to the middle mast 20.

[0036] When the lift cylinder 32 is extended, that is, when the operator keeps the lift lever 59 in the raised position, the controller 61 controls the switching valve 62 to remain open even if the holding pressure of the full free cylinder 37 drops below the threshold. When the piston 34 abuts against the upper part of the cylinder body 33 and the extension of the piston rod 35 stops, the middle mast 20 is raised to its highest position relative to the outer mast 19, and the inner mast 21 is raised to its highest position relative to the middle mast 20. Therefore, the forks 28 are in their uppermost positions.

[0037] However, the amount of hydraulic oil in the cylinder space 43 of the full free cylinder 37 may increase beyond a certain level. This increase in hydraulic oil is caused by a deterioration in the function of a sealing member (not shown) provided in the full free cylinder 37, resulting in hydraulic oil leakage. For example, in the case of a cargo handling device without a switching valve 62, when the amount of hydraulic oil in the cylinder space 43 increases, the holding pressure of the full free cylinder 37 becomes greater than the holding pressure of the lift cylinder 32, not just before the piston 39 has completed its ascent, but before the piston 39 has fully ascended. As a result, hydraulic oil is supplied to the lift cylinder 32. Therefore, in this embodiment, the switching valve 62 is controlled to a closed state so that hydraulic oil is not supplied to the lift cylinder 32 while the piston 39 is ascending, and hydraulic oil is not supplied to the lift cylinder 32 unless the holding pressure of the full free cylinder 37 exceeds a threshold value.

[0038] The cargo handling apparatus 12 according to this embodiment has the following advantages. (1) When the lift bracket 23 is raised, the control valve 53 supplies hydraulic oil to the hydraulic oil chamber 41 through the third pipe 56, which serves as the first hydraulic oil passage, to extend the full free cylinder 37. Before the full free cylinder 37 fully extends, the pressure of the shock-reducing hydraulic oil in the cylinder space 43 increases, causing hydraulic oil to flow out of the cylinder space 43 and mitigating shock. When the pressure in the third pipe 56 exceeds a threshold, the switching valve 62 switches from a closed state to an open state, enabling the supply of hydraulic oil to the lift cylinder 32. Therefore, even if the full free cylinder 37 extends with an increased amount of hydraulic oil in the cylinder space 43, the lift cylinder 32 will not extend at any time other than when the full free cylinder 37 has almost stopped rising. As a result, it is possible to achieve shock reduction (shockless) for the full free cylinder 37 and prevent the lift cylinder 32 from operating before the full free cylinder 37 has stopped rising.

[0039] (2) When the full free cylinder 37 is fully extended and the lift cylinder 32 is extended, the switching valve 62 is in an open state. When the switching valve 62 is in an open state and the lift lever 59 is in the raised position, the pressure in the third pipe 56 is lower than the threshold value. below Even if this occurs, the switching valve 62 remains open. As a result, the supply of hydraulic oil to the lift cylinder 32 can be continued, and the lift cylinder 32 can be lifted stably.

[0040] (3) The threshold value of the holding pressure of the full free cylinder 37 is set, so that the full free cylinder 37 During extension, regardless of the holding pressure of the lift cylinder 32, the switching valve 62 can be switched to supply hydraulic oil to the lift cylinder 32.

[0041] The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the spirit of the invention. For example, the following modifications may be made.

[0042] In the above embodiment, the pressure sensor is provided in the third pipe, but this is not limiting. For example, the pressure sensor may be provided in the hydraulic oil chamber of the full free cylinder. In this case, the pressure sensor is less susceptible to pressure loss in the third pipe compared to when the pressure sensor is provided in the third pipe, and therefore the relationship between the load on the full free cylinder received from the lift bracket and the pressure sensor is more accurate. In the above embodiment, a three-stage full free mast (FSV) loading device has been described as an example, but the loading device of a forklift is not limited to this. For example, the loading device of a forklift may be a two-stage full free mast (FV) loading device that does not have a middle mast. In the above embodiment, the forklift is an engine forklift, but the forklift is not limited to this. For example, the forklift may be a battery forklift or a fuel cell forklift. [Explanation of symbols]

[0043] 10. Forklift 11 Body 12 Cargo handling equipment 19 Outer Mast 21 Innamast 23 Lift bracket 28 Fork 32 Lift cylinder 37 Full free cylinder 38 Cylinder body 39 Piston 40 Piston rod 41 Hydraulic oil chamber 42 Shockless mechanism 43 Cylinder space 44 Rod Space 45 Aperture Passage 50 Hydraulic circuit 52 Hydraulic oil pump 53 Control valve 56 3rd piping (1st hydraulic oil path) 57 4th piping (2nd hydraulic oil path) 59 Lift lever 60 Lever sensor 61 Controller 62 Switching valve 63 Check valve 64 Pressure Sensor

Claims

1. Outer must and an inner mast that can be raised and lowered relative to the outer mast; a lift bracket that can be raised and lowered relative to the inner mast; a full free cylinder that raises and lowers the lift bracket relative to the inner mast; a lift cylinder for raising and lowering the inner mast relative to the outer mast; A hydraulic oil tank that stores hydraulic oil for the lift cylinder; a hydraulic oil pump that pumps hydraulic oil from the hydraulic oil tank; a hydraulic oil pump that pumps hydraulic oil; a lift lever for operating the lift bracket to raise and lower; a control valve that controls the supply and discharge of hydraulic oil to the full free cylinder and the lift cylinder in conjunction with the operation of the lift lever; a first hydraulic oil passage connecting the control valve and the full free cylinder and passing hydraulic oil from the control valve to the full free cylinder; a second hydraulic oil passage branched from the first hydraulic oil passage and connected to the lift cylinder, for passing hydraulic oil from the first hydraulic oil passage to the lift cylinder; In a loading device of a forklift, the control valve is arranged closer to the hydraulic oil tank than a branch portion of the first hydraulic oil line to the second hydraulic oil line, The full free cylinder is A cylinder body; a piston that is slidable up and down inside the cylinder body; a piston rod connected to the piston and extending and retracting relative to the cylinder body; a full free cylinder hydraulic oil chamber formed below the piston in the cylinder body and supplied with hydraulic oil via the first hydraulic oil passage; a cylinder space formed above the piston in the cylinder body between the piston rod and the cylinder body, in which shock-reducing hydraulic oil is stored to prevent shock when the piston stops rising; a rod space formed inside the piston rod; a throttle passage formed in the piston rod and communicating the rod space with the cylinder space, a switching valve provided in the second hydraulic oil passage, which switches between flow and cut-off of hydraulic oil from the first hydraulic oil passage to the second hydraulic oil passage by opening and closing, and when hydraulic oil is supplied to the full free cylinder by the control valve, cuts off the supply of hydraulic oil to the lift cylinder by closing the valve and allows the supply of hydraulic oil to the lift cylinder by opening the valve; a pressure sensor for detecting a pressure in the first hydraulic oil passage; a controller that controls opening and closing of the switching valve, a control valve configured to supply hydraulic oil to the full free cylinder when the control valve is in a closed state and the pressure sensor detects a pressure exceeding a preset threshold value;

2. a lever sensor for detecting the operation position of the lift lever; 2. The forklift loading device according to claim 1, wherein the controller does not close the switching valve even if the pressure in the first hydraulic oil line falls below a threshold value when the switching valve is open and the lift lever is in the raised position.

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