forklift

Abstract

To provide a forklift that prevents an excessive load from being applied to a front lift chain in a full-free three-stage mast.SOLUTION: A stopper mechanism with a stopper part and a stopped part to which the stopper part engages includes a chain tension measuring device for measuring the tension of a front lift chain 46, a controller 54 connected to the chain tension measuring device, and a warning device controlled by the controller. When a middle mast 20 is raised through operation of a rear lift cylinder 35, the controller 54 determines whether a chain tension measured by the chain tension measuring device is greater than a chain tension calculation value calculated based on an internal pressure of the rear lift cylinder 35, and controls the warning device to issue an alarm if it is determined that the measured chain tension is greater than the chain tension calculation value.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a forklift. [Background technology]

[0002] Some forklifts are equipped with a three-section fully free-standing mast loading device. This three-section fully free-standing mast includes an outer mast, a middle mast, an inner mast, a rear lift cylinder for raising and lowering the middle mast, and a front lift cylinder for raising and lowering the lift bracket. The three-section fully free-standing mast also includes a rear lift chain connected to the outer mast and inner mast, and a front lift chain connected to the inner mast and lift bracket. Some forklifts are equipped with a stopper mechanism that includes a stopper portion on the lift bracket and a stoppered portion on the inner mast that engages with the stopper portion. The stopper mechanism is provided to prevent the lift bracket from slipping out of the inner mast. Incidentally, if the lift bracket is raised without properly adjusting the length of the front lift chain, or if the inner mast is lowered relative to the middle mast while the forks on the lift bracket are supported on a shelf, the stopper portion will engage with the stoppered portion.

[0003] Meanwhile, there is a known technology for preventing the free fall of forks due to loose lift chains and preventing damage to equipment due to impacts (see, for example, Patent Document 1). The forklift disclosed in Patent Document 1 has a mast assembly installed in front of the forklift body, with a load support device that moves up and down. The mast assembly is composed of a pair of fixed masts and a lifting mast. A chain attachment bracket fixed to the fixed mast has a hole formed therein, through which an anchor bolt that connects one end of the lift chain is inserted. A coil spring is inserted around the outer periphery of the anchor bolt, between a lower plate inserted and fixed to the lower end of the anchor bolt protruding downward from the underside of the chain attachment bracket, and an upper plate inserted near the bracket of the anchor bolt. Both ends of the lift chain are fixed to the bracket and the load support device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-265191 Summary of the Invention [Problem to be solved by the invention]

[0005] In a forklift equipped with a conventional three-stage fully free mast, the stopper and the stopped portion are locked together, preventing the lift bracket from slipping out of the inner mast. However, even after the stopper and the stopped portion are locked together, continuing to lift the forks can cause excessive loads on the front lift chain. This excessive load on the front lift chain can result in damage to the lift chain. Meanwhile, the technology disclosed in Patent Document 1 merely uses a coil spring to absorb the impact caused by loosening of the lift chain.

[0006] The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a forklift that prevents excessive load from being placed on the front lift chain in a full free three-stage mast. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides a construction machine comprising a pair of outer masts, a pair of middle masts which can be raised and lowered relative to the pair of outer masts, a pair of inner masts which can be raised and lowered relative to the pair of middle masts, lift brackets which can be raised and lowered relative to the pair of inner masts, rear lift cylinders which raise and lower the pair of middle masts relative to the pair of outer masts, front lift cylinders which raise and lower the lift brackets relative to the pair of inner masts, rear lift chains which are connected to the pair of outer masts and the pair of inner masts via the pair of middle masts and which raise and lower the pair of inner masts by extension and contraction of the rear lift cylinders, front lift chains which raise and lower the lift brackets by extension and contraction of the front lift cylinders, and a construction machine comprising: a lift chain for lifting and lowering the pair of inner masts; and a stopper mechanism that locks the lift bracket to the mast, the stopper mechanism having a stopped portion and a stopper portion to which the stopped portion locks, the forklift having a chain tension measuring device that measures the tension of the front lift chain, a controller connected to the chain tension measuring device, and an alarm controlled by the controller, wherein when the pair of middle masts are raised by operation of the rear lift cylinders, the controller determines whether the chain tension measurement value measured by the chain tension measuring device is greater than a chain tension calculation value calculated based on the internal pressure of the rear lift cylinders, and if it is determined that the chain tension measurement value is greater than the chain tension calculation value, it controls the alarm to issue a warning.

[0008] In this invention, when the rear lift cylinder is actuated to raise the middle mast, the controller determines whether the measured chain tension measured by the chain tension measuring device is greater than the calculated chain tension calculated based on the internal pressure of the rear lift cylinder. If the measured chain tension is determined to be greater than the calculated chain tension, the controller controls the alarm to issue a warning. Therefore, the forklift operator can know from the controller's determination that the stopper portion and the stopped portion are engaged. As a result, excessive load on the front lift chain in a fully free three-section mast can be prevented.

[0009] The forklift truck may further include a middle mast rise detector that detects the rise of the pair of middle masts due to the operation of the rear lift cylinders. In this case, the middle mast lift detector can detect the lifting of the pair of middle masts due to the operation of the rear lift cylinders.

[0010] The forklift truck may further include a chain anchor bolt for fixing the front lift chain to the inner mast, and the chain tension measuring device may be a strain detection sensor for detecting strain in the chain anchor bolt. In this case, the strain detection sensor can measure the tension of the front lift chain by detecting the strain of the chain anchor bolt.

[0011] In the forklift truck described above, the middle mast rise detector may be a height sensor that detects the height of the pair of middle masts, and the controller may be configured to determine whether the rear lift cylinders are extending or retracting based on the detection by the height sensor. In this case, the controller can determine whether the rear lift cylinder is extending or retracting using a height sensor that detects the height of the middle mast. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a forklift truck that prevents an excessive load from being applied to the front lift chain in a full free three-stage mast. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a side view of a forklift according to an embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view of the loading device of the forklift truck as seen from the front. [Figure 3] FIG. 1 is an explanatory diagram illustrating a configuration of a loading device of a forklift truck. [Figure 4] FIG. 2 is a perspective view of the main part of the loading device of the forklift truck as seen from the rear. [Figure 5] FIG. 2 is a perspective view of the upper part of the loading device of the forklift truck as seen from the front. [Figure 6] FIG. 10 is a flowchart showing a procedure for detecting engagement of the stopper body. DETAILED DESCRIPTION OF THE INVENTION

[0014] A forklift according to this embodiment will be described below with reference to the drawings. The forklift according to this embodiment is a forklift equipped with a three-stage fully free-standing mast. The terms "front and back," "left and right," and "up and down" that specify directions are used based on the position of the forklift operator seated in the driver's seat and facing the forward direction of the forklift.

[0015] 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.

[0016] 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.

[0017] As shown in Figure 2, the cargo handling apparatus 12 is equipped with a full free three-section 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.

[0018] As shown in FIG. 2, the upper ends of the pair of left and right outer masts 19 are connected by an outer upper beam 24. As shown in FIG. 3, the lower parts of the pair of left and right outer masts 19 are connected by an outer lower beam 25. The upper ends of the pair of left and right middle masts 20 are connected by a middle upper beam 26 (see FIG. 2). The lower parts of the pair of left and right middle masts 20 are connected by a middle lower beam 27. The upper ends of the pair of left and right inner masts 21 are connected by an inner upper beam 28. The lower parts of the pair of left and right inner masts 21 are connected by an inner lower beam 29 (see FIG. 2). As shown in FIG. 4, the pair of left and right inner masts 21 are connected at their intermediate positions by an inner intermediate beam 30. The lift bracket 23 is equipped with a pair of left and right forks 31 and a backrest 32. The left and right forks 31 lift up and support a load. The backrest 32 supports the rear of the load supported by the pair of left and right forks 31.

[0019] As shown in Figure 3, one end of a rear lift chain 33 is fixed to the upper part of the outer mast 19. A lift chain anchor bracket (not shown) is attached to the outer mast 19, and a chain anchor bolt (not shown) is fixed to the lift chain anchor bracket. One end of the rear lift chain 33 is connected to the upper end of the chain anchor bolt.

[0020] A chain wheel 34 on which a rear lift chain 33 is looped is provided on the upper part of the middle mast 20. The rear lift chain 33 is looped around the chain wheel 34, and the other end of the rear lift chain 33 is fixed to the lower part of the inner mast 21. Therefore, the rear lift chain 33 is connected to the outer mast 19 and the inner mast 21 via the middle mast 20. The outer mast 19 is provided with a rear lift cylinder 35 that is operated by the supply and discharge of hydraulic oil. By operating the rear lift cylinder 35, the middle mast 20 moves up and down inside the outer mast 19, and the inner mast 21 moves up and down inside the middle mast 20.

[0021] As shown in Figure 3, the rear lift cylinder 35 includes a cylinder body 36, a piston 37 that slides inside the cylinder body 36, and a piston rod 38 that is connected to the piston 37 and extends and retracts relative to the cylinder body 36. A hydraulic oil chamber 39 is formed in the cylinder body 36 below the piston 37, serving as a lift cylinder hydraulic oil chamber. When hydraulic oil is supplied to the hydraulic oil chamber 39, the piston 37 rises in the cylinder body 36 and the piston rod 38 extends. When hydraulic oil is discharged from the hydraulic oil chamber 39, the piston 37 descends in the cylinder body 36 and the piston rod 38 retracts. The upper end of the piston rod 38 is connected to the middle mast 20.

[0022] As shown in FIG. 3, a front lift cylinder 40 is provided upright on the inner lower beam 29 of the inner mast 21. The front lift cylinder 40 is a hydraulic cylinder for raising and lowering the lift bracket 23 relative to the inner mast 21. As shown in FIG. 3, the front lift cylinder 40 includes a cylinder body 41, a piston 42 that slides inside the cylinder body 41, and a piston rod 43 that is connected to the piston 42 and extends and retracts relative to the cylinder body 41. A hydraulic oil chamber 44 serving as a full free cylinder hydraulic oil chamber is formed below the piston 42 in the cylinder body 41. When hydraulic oil is discharged from the hydraulic oil chamber 44, the piston 42 descends the cylinder body 41 and the piston rod 43 retracts. The pressure-receiving area of ​​the hydraulic oil chamber 44 is set larger than that of the hydraulic oil chamber 39 of the rear lift cylinder 35. Note that the hose and hose pulley that supply hydraulic oil to the front lift cylinder 40 are not shown in FIG. 4.

[0023] As shown in Figure 4, a pair of left and right chain wheels 45 are provided on the upper end of the piston rod 43. A front lift chain 46 is looped around the chain wheels 45, connecting the inner mast 21 and the lift bracket 23. One end of the front lift chain 46 is connected to the inner intermediate beam 30 via a chain anchor bolt 47. The other end of the front lift chain 46 is connected to the lower part of the lift bracket 23 (see Figure 2). Therefore, when the piston rod 43 of the front lift cylinder 40 rises, the lift bracket 23 rises without raising the inner mast 21 or the middle mast 20. The outer mast 19 is provided with a lift height sensor 48 that detects whether the middle mast 20 is raised (see Figure 3). The lift height sensor 48 is provided to detect whether the rear lift cylinder 35 is extending or retracting, and is a sensor that sends an ON signal when the middle mast 20 is raised.

[0024] 3 and 5, the cargo handling apparatus 12 of this embodiment is equipped with a stopper mechanism 50. The stopper mechanism 50 is a mechanism for preventing the lift bracket 23 from slipping out of the inner mast 21 due to insufficient adjustment of the length of the rear lift chain 33. The stopper mechanism 50 has a stopped body 51 provided on the upper part of the lift bracket 23 as a portion to be stopped, and a stopper body 52 provided on the inner upper beam 28 of the inner mast 21 as a portion to be stopped.

[0025] The stoppered body 51 is a shaft-shaped member fixed near the upper end of the lift bracket 23. The stoppered body 51 protrudes from the rear surface of the lift bracket 23 so as to protrude toward the inner upper beam 28 of the inner mast 21. The stopper body 52 is a block-shaped member fixed to the front surface of the inner upper beam 28. The stopper body 52 protrudes from the front surface of the inner upper beam 28 so as to protrude toward the lift bracket 23 in accordance with the position of the stoppered body 51. Therefore, even if the length of the front lift chain 46 is improperly adjusted, the stoppered body 51 is engaged with the stopper body 52, preventing the lift bracket 23 from slipping off the inner mast 21. Furthermore, even if the inner mast 21 is lowered with the forks 31 placed on a shelf or the like, the stoppered body 51 is engaged with the stopper body 52, preventing the lift bracket 23 from slipping off the inner mast 21.

[0026] The forklift 10 of this embodiment also includes a chain tension measuring device that measures the tension of the front lift chain 46. As shown in Fig. 4, the chain tension measuring device is a strain detection sensor 53 attached to the upper end of the chain anchor bolt 47. The strain detection sensor 53 is a strain gauge or load cell that detects the axial strain of the chain anchor bolt 47. The strain detection sensor 53 is connected to a controller 54 mounted on the forklift 10, and a signal detected by the strain detection sensor 53 is transmitted to the controller 54.

[0027] The controller 54 controls each component of the forklift 10 and receives signals from various sensors, including the strain detection sensor 53. The controller 54 includes a CPU and a memory unit (not shown) such as RAM. The controller 54 may also include dedicated hardware, such as an application-specific integrated circuit (ASIC), that performs at least some of the various processes. The controller 54 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 the 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 dedicated computer. The controller 54 is connected to an alarm 55 provided in the driver's seat 13, which warns the operator by visual display or audible warning.

[0028] A load based on at least the weights of the inner mast 21, middle mast 20, front lift cylinder 40, and rear lift chain 33 acts on the rear lift chain 33. For example, when the fork 31 is not in contact with the road surface, the weights of the inner mast 21, front lift cylinder 40, and rear lift chain 33, as well as the lift bracket 23 and fork 31, act on the rear lift chain 33. An internal pressure corresponding to these weights is generated in the hydraulic oil chamber 39 of the rear lift cylinder 35. A pressure sensor (not shown) that detects the internal pressure of the rear lift cylinder 35 or the front lift cylinder 40 is connected to the controller 54. The internal pressure measured by the pressure sensor is transmitted to the controller 54.

[0029] A load based on at least the weight of the lift bracket 23, fork 31, backrest 32, and front lift chain 46 acts on the front lift chain 46. For example, when the fork 31 is not in contact with the shelf, the weight of the lift bracket 23, fork 31, backrest 32, and front lift chain 46 acts on the front lift chain 46. An internal pressure corresponding to this weight is generated in the hydraulic oil chamber 44 of the front lift cylinder 40. In addition, a tensile load is always applied to the front lift chain 46, and this tensile load tries to pull up the chain anchor bolt 47, causing strain in the chain anchor bolt 47 that stretches it in the axial direction. For this reason, the strain detection sensor 53 detects the strain and transmits a signal to the controller 54.

[0030] Incidentally, if the length of the front lift chain 46 is not adjusted properly, the extension of the front lift cylinder 40 may cause the stopped object 51 to become engaged with the stopper body 52 when the lift bracket 23 is raised. The engagement of the stopped object 51 with the stopper body 52 prevents the lift bracket 23 from jumping out of the inner mast 21. If the extension of the front lift cylinder 40 continues with the stopped object 51 engaged with the stopper body 52, the load acting on the front lift chain 46 will increase. Furthermore, after the extension of the front lift cylinder 40, the rear lift cylinder 35 will further extend.

[0031] In this embodiment, the controller 54 obtains the measured chain tension of the front lift chain 46 from the strain detection sensor 53. The controller 54 also calculates the calculated chain tension of the front lift chain 46 and the rear lift chain 33 based on the internal pressure of the rear lift cylinder 35 or the front lift cylinder 40. When the rear lift cylinder 35 is actuated to raise the middle mast 20, the controller 54 determines whether the measured chain tension is greater than the calculated chain tension, and determines whether the stopped body 51 and the stopper body 52 are engaged. When it is determined that the stopped body 51 is engaged with the stopper body 52, the controller 54 activates the alarm 55.

[0032] 6 is a flow diagram for determining whether the stopped body 51 is engaged with the stopper body 52. ​​The controller 54 determines whether the lift height sensor 48 is ON (step S01). When the lift height sensor 48 is ON, the middle mast 20 is raised by the operation of the rear lift cylinder 35, and therefore, the state is in the rear lift cylinder operation range (step S02). Note that, when it is determined in step S01 that the lift height sensor 48 is OFF, the rear lift cylinder 35 is not operating, and the state is in the front lift cylinder operation range (step S07). In this case, the process returns from step S07 to step S01.

[0033] When the middle mast 20 is at the lowest position, the strain detection sensor 53 then detects strain on the chain anchor bolt 47 (step S03). The tension of the front lift chain 46 is measured by the strain detection sensor 53. Next, the controller 54 calculates the chain tension calculation value Tfc of the front lift chain 46, and determines whether the chain tension measurement value Tfa measured by the strain detection sensor 53 is greater than the calculated chain tension calculation value Tfc (step S04).

[0034] The calculated chain tension value Tfc can be calculated using the following formula, and a program for calculating the calculated chain tension value Tfc is stored in the controller 54. The calculated chain tension value Trc of the rear lift chain 33 can be calculated based on the internal pressure P, the cross-sectional area A1 of the rear lift cylinder 35, and the weight Mm of the middle mast 20. The calculated chain tension value Tfc can also be calculated based on the calculated chain tension value Trc, the weight Mi of the inner mast 21, and the weight Mfcyl of the front lift cylinder 40. Trc=(P×A1-Mm) / 2 (Formula 1) Tfc = Trc - Mi - Mfcyl (Equation 2) Tfc=(P×A1-Mm) / 2-Mi-Mfcyl (Formula 3) A1: Cross-sectional area of ​​rear lift cylinder 35 (a pair of two cylinders, left and right) A2: Cross-sectional area of ​​the front lift cylinder 40 Mi: Weight of inner mast 21 Mm: Weight of mid-mast 20 Mfcyl: Front lift cylinder 40 weight P: Internal pressure Tfa: Chain tension measurement value of the measured front lift chain 46 Tfc: Calculated chain tension for front lift chain 46 Trc: Calculated chain tension for rear lift chain 33 The internal pressure P of the front lift cylinder 40 and the rear lift cylinder 35 is the same, and the cross-sectional area A2 of the front lift cylinder 40 is larger than the cross-sectional area A1 of the rear lift cylinder 35 (A1 <A2)。

[0035] If it is determined that the measured chain tension value Tfa is greater than the calculated chain tension value Tfc (Tfa>Tfc), the controller 54 determines that the stopped body 51 is locked by the stopper body 52 (step S05). At this time, the measured chain tension value Tfa of the front lift chain 46 is expressed by the following equation. Tfa = (P × A2) / 2 (Equation 4) The magnitude relationship between the calculated chain tension value Tfc and the measured chain tension value Tfa is derived from the following equation. Tfa-Tfc={P×(A2-A1)+Mm+2Mi+2Mfcyl} / 2>0 ...(Formula 5) Tfa>Tfc (Equation 6) That is, the measured chain tension Tfa of the front lift chain 46 when the stopped body 51 and the stopper body 52 are engaged becomes greater than the calculated chain tension Tfc calculated based on the internal pressure P.

[0036] When the stopped body 51 is locked by the stopper body 52, the controller 54 issues a warning using the alarm 55 (step S06). If the measured chain tension Tfa is equal to or less than the calculated chain tension Tfc in step S05, the stopped body 51 is not locked by the stopper body 52 (step S08). In this case, the process returns to step S01. Note that when the stopped body 51 and the stopper body 52 are not locked, the measured chain tension Tfa and the calculated chain tension Tfc may be equal (Tfa = Tfc). Specifically, when the piston rod 43 of the front lift cylinder 40 is not fully extended, i.e., when the hydraulic oil chamber 44 of the front lift cylinder 40 is below the relief pressure, the measured chain tension Tfa and the calculated chain tension Tfc become equal. On the other hand, when the hydraulic oil chamber 44 is at the relief pressure, which is the maximum extension of the piston rod 43 of the front lift cylinder 40, the measured chain tension value Tfa becomes smaller than the calculated chain tension value Tfc (Tfa <Tfc)。

[0037] Next, the operation of the forklift 10 of this embodiment will be described. When the forks 31 are raised, hydraulic oil is supplied to the hydraulic oil chamber 44 of the front lift cylinder 40 and the hydraulic oil chamber 39 of the rear lift cylinder 35. Because the hydraulic oil chamber 44 and the hydraulic oil chamber 39 are connected by piping, the piston rod 43 of the front lift cylinder 40, whose cross-sectional area A2 is larger than the cross-sectional area A1, rises before the piston rod 38 of the rear lift cylinder 35. When the front lift cylinder 40 is raised, the internal pressures P of the hydraulic oil chamber 44 of the front lift cylinder 40 and the hydraulic oil chamber 39 of the rear lift cylinder 35 are equal.

[0038] When the piston rod 43 of the front lift cylinder 40 reaches its uppermost position, the piston rod 43 of the rear lift cylinder 35 begins to rise. As the piston rod 43 of the rear lift cylinder 35 rises, the inner mast 21 and middle mast 20 rise. When the middle mast 20 rises, the height sensor 48 transmits an ON signal to the controller 54. When the rear lift cylinder 35 is extended, the hydraulic oil chamber 44 of the front lift cylinder 40 and the hydraulic oil chamber 39 of the rear lift cylinder 35 have the same internal pressure P.

[0039] In the forklift 10 of this embodiment, if the length of the front lift chain 46 is adjusted appropriately, the stopper object 51 of the lift bracket 23 will not engage with the stopper object 52 of the inner mast 21 even when the fork 31 is raised. In the operating range of the rear lift cylinder 35, where the stopper object 51 does not engage with the stopper object 52 and the lift height sensor 48 is ON, the controller 54 determines that the measured chain tension Tfa is equal to or less than the calculated chain tension Tfc. However, if the length of the front lift chain 46 is not adjusted appropriately, the stopper object 51 may engage with the stopper object 52 when the fork 31 is raised.

[0040] When the fork 31 is raised while the stopped object 51 is engaged with the stopper body 52, the tension of the front lift chain 46 increases. When the piston rod 38 of the rear lift cylinder 35 is raised, the lift height sensor 48 transmits an ON signal to the controller 54. The strain of the chain anchor bolt 47 increases as the tension of the front lift chain 46 increases. The strain detection sensor 53 measures the measured chain tension value Tfa. The controller 54 determines that the measured chain tension value Tfa is greater than the calculated chain tension value Tfc, and therefore the stopped object 51 is engaged with the stopper body 52. ​​The controller 54 determines that the stopped object 51 is engaged with the stopper body 52 and activates the alarm 55.

[0041] The operator of the forklift 10 receives a warning from the alarm 55 and recognizes that the stopped body 51 is locked by the stopper body 52. ​​Then, by stopping the lifting of the forks 31 and lowering the forks 31, the occurrence of excessive load on the front lift chain 46 is prevented.

[0042] The forklift 10 of this embodiment has the following advantages. (1) When the rear lift cylinder 35 is actuated to raise the middle mast 20, the controller 54 determines whether the measured chain tension value Tfa is greater than the calculated chain tension value Tfc, which is calculated based on the internal pressure P of the rear lift cylinder 35. If it is determined that the measured chain tension value Tfa is greater than the calculated chain tension value Tfc, the controller 54 controls the alarm 55 to issue a warning. Therefore, the operator of the forklift 10 can know from the determination by the controller 54 that the stopped body 51 and the stopper body 52 are locked together.

[0043] (2) A middle mast rise detector is provided to detect the rise of the middle mast 20 due to the operation of the rear lift cylinder 35. Therefore, the lift height sensor 48 can detect the rise of the middle mast 20 due to the operation of the rear lift cylinder 35.

[0044] (3) The front lift chain 46 is provided with a chain anchor bolt 47 that secures the front lift chain 46 to the inner mast 21, and the chain tension measuring device is a strain detection sensor 53 that detects the strain of the chain anchor bolt 47. Therefore, the strain detection sensor 53 can measure the tension of the front lift chain 46 by detecting the strain of the chain anchor bolt 47.

[0045] (4) The middle mast rise detector is a height sensor 48 that detects the height of the pair of middle masts 20, and the controller 54 can determine whether the rear lift cylinders 35 are extending or retracting based on the detection by the height sensor 48. In addition, since the height sensor 48 that detects the height of the middle masts 20 can be used to determine whether the rear lift cylinders 35 are extending or retracting, the present invention can be applied to existing forklifts that are equipped with a height sensor.

[0046] 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.

[0047] In the above embodiment, the stopper detector detects the strain of the chain anchor bolt connected to the inner intermediate beam, but this is not limited to this. The stopper detector may also measure the chain tension by detecting the strain of the chain anchor bolt connected to the inner mast. In the above embodiment, when the measured chain tension is determined to be greater than the calculated chain tension, the controller controls the alarm to issue a warning. However, this is not limited to this. When the measured chain tension is determined to be greater than the calculated chain tension, the controller may, for example, issue a warning and open an unload valve in the hydraulic circuit to stop operation of the rear lift cylinder. In addition, in the case of a battery-powered forklift, the controller may stop the load-handling pump. In the above embodiment, the middle mast rise detector is a lift height sensor, but is not limited to this. The middle mast rise detector may be, for example, a means for detecting the rise of the middle mast based on the movement of the lift chain, or a means for detecting the rise of the middle mast based on the movement of the piston rod of the rear cylinder. In the above embodiment, an engine forklift is used as the forklift, but the present invention is not limited to this. The forklift may be an electric forklift. Furthermore, the forklift may be not only a forklift with a counterweight but also a reach forklift. [Explanation of symbols]

[0048] 10. Forklift 11 Body 12 Cargo handling equipment 13 Driver's seat 19 Outer Mast 20 Middlemast 21 Innamast 22 Mast 23 Lift bracket 31 Fork 33 Rear lift chain 35 Rear lift cylinder 40 Front lift cylinder 46 Front lift chain 47 Chain anchor bolt 48 Height sensor (middle mast rise detector) 50 Stopper mechanism 51 Stopped body (stopped portion) 52 Stopper body (stopper part) 53 Strain detection sensor (chain tension measurement section) 54 Controller 55 Alarm Tfa chain tension measurement Tfc chain tension calculation value Trc chain tension calculation value A1 Rear lift cylinder cross section area A2 Front lift cylinder cross section area Mi inner mast weight Mm Midmast Weight Mfcyl front lift cylinder weight P internal pressure

Claims

1. A pair of outer masts, a pair of middle masts that can be raised and lowered relative to the pair of outer masts; a pair of inner masts that can be raised and lowered relative to the pair of middle masts; a lift bracket that can be raised and lowered relative to the pair of inner masts; a rear lift cylinder for raising and lowering the pair of middle masts relative to the pair of outer masts; a front lift cylinder for raising and lowering the lift bracket relative to the pair of inner masts; a rear lift chain connected to the pair of outer masts and the pair of inner masts via the pair of middle masts, and configured to raise and lower the pair of inner masts by extension and contraction of the rear lift cylinders; a front lift chain that raises and lowers the lift bracket by extension and contraction of the front lift cylinder; a stopper mechanism for locking the lift bracket to the pair of inner masts, the stopper mechanism includes a stopped portion and a stopper portion to which the stopped portion is engaged, a chain tension measuring device that measures the tension of the front lift chain; a controller connected to the chain tension measuring device; an alarm controlled by the controller; The controller When the pair of middle masts are raised by the operation of the rear lift cylinders, a determination unit that determines whether a chain tension measurement value measured by the chain tension measuring device is greater than a calculated chain tension value calculated based on the internal pressure of the rear lift cylinder, and that controls the alarm to issue a warning when it is determined that the measured chain tension value is greater than the calculated chain tension value.

2. 2. The forklift according to claim 1, further comprising a middle mast rise detector for detecting the rise of the pair of middle masts due to the operation of the rear lift cylinders.

3. a chain anchor bolt for fixing the front lift chain to the inner mast; 3. The forklift according to claim 1, wherein the chain tension measuring device is a strain detection sensor that detects strain in the chain anchor bolt.

4. the middle mast rise detector is a height sensor that detects the height of the pair of middle masts, 3. The forklift according to claim 2, wherein the controller determines whether the rear lift cylinder is extended or retracted based on the detection by the height sensor.

Images