Work vehicle

Abstract

Provided is a material handling vehicle capable of measuring the load acting on a load support unit by excluding the influence of the operating pressure generated during the lifting and lowering of the load support unit. 【Solution means】The forklift (material handling vehicle) includes a fork (load support unit) for supporting a load, a lift cylinder for raising and lowering the fork, a pump 32 for sending hydraulic oil to the lift cylinder, a motor 33 (pump drive unit) for driving the pump 32, a lift control valve for controlling the flow rate of the hydraulic oil, a valve opening detection unit 61 for detecting the opening degree of the lift control valve, a hydraulic pressure sensor 43 (hydraulic pressure detection unit) for detecting the hydraulic pressure in the lift cylinder, a load calculation unit 51 for calculating the load acting on the fork based on the hydraulic pressure, a correction amount calculation unit 54 for calculating a correction amount based on the opening degree, and a load correction unit 55 for correcting the load based on the correction amount.

Description

Technical Field

[0001] The present invention relates to a material handling vehicle that measures the load acting on a load support part.

Background Art

[0002] Patent Document 1 describes a forklift as a material handling vehicle capable of measuring a load, which includes a fork as a load support part, a lift cylinder for raising and lowering the fork, and a hydraulic pressure sensor for detecting the hydraulic pressure of the hydraulic oil flowing between a tank and the lift cylinder.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the configuration of Patent Document 1, there is a problem that the load measured based on the hydraulic pressure during the raising and lowering of the fork includes the influence of the operating pressure (the pressure change generated when the lift cylinder operates). Therefore, when the fork lifts a load during the upward movement of the fork, there are inconveniences such as being unable to accurately measure the weight of the load, and when the fork places a load during the downward movement of the fork, there is an inconvenience that it is impossible to accurately detect that the fork has separated from the load.

[0005] In view of the above circumstances, the present invention has been made, and an object thereof is to provide a material handling vehicle capable of measuring the load acting on a load support part by excluding the influence of the operating pressure generated during the raising and lowering of the load support part.

Means for Solving the Problems

[0006] To solve the above problems, the cargo handling vehicle of the present invention includes a cargo support portion for supporting cargo, a lift cylinder for raising and lowering the cargo support portion, a pump for sending hydraulic oil to the lift cylinder, a pump drive portion for driving the pump, a lift control valve for controlling the flow rate of the hydraulic oil, a valve opening detection portion for detecting the opening degree of the lift control valve, a hydraulic pressure detection portion for detecting the hydraulic pressure in the lift cylinder, a load calculation portion for calculating the load acting on the cargo support portion based on the hydraulic pressure, a correction amount calculation portion for calculating a correction amount for correcting the load based on the opening degree, and a load correction portion for correcting the load based on the correction amount.

[0007] Further, it is preferable to include a rotation speed detection portion for detecting the rotation speed of the pump drive portion, and the correction amount calculation portion calculates the correction amount based on the opening degree and the rotation speed.

[0008] Further, it is preferable to include a lift lever operated to control the opening degree, and the valve opening detection portion is composed of a lever sensor for detecting the operation amount of the lift lever and a valve opening calculation portion for calculating the opening degree based on the operation amount.

[0009] Further, it includes a notification portion for notifying that the load is an excessive load, and a notification control portion for controlling the notification portion. The notification control portion preferably operates the notification portion when the cargo support portion is rising and the load after correction based on the correction amount becomes larger than a predetermined excessive load determination threshold value.

[0010] Further, it includes a pump control portion for controlling the pump drive portion. The pump control portion preferably controls the pump drive portion to limit the rise of the cargo support portion when the cargo support portion is rising and the load after correction based on the correction amount becomes larger than a predetermined excessive load determination threshold value.

[0011] Further, a fork as the load support part, a key switch configured to be switchable between a key-on state and a key-off state, a notification part for notifying that the fork is not grounded to the ground, and a notification control part for controlling the notification part are provided. The lift cylinder is configured such that when the fork is grounded to the ground, the hydraulic pressure is lower than when the fork is not grounded to the ground. The notification control part preferably operates the notification part when the key switch is in the key-off state and the load is equal to or greater than a predetermined grounding determination threshold value.

Effect of the Invention

[0012] According to the present invention, it is possible to provide a cargo handling vehicle capable of measuring the load acting on the load support part by excluding the influence of the operating pressure generated during the lifting and lowering of the load support part.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0014] With reference to the drawings, a forklift 1 which is a cargo handling vehicle according to an embodiment of the present invention will be described. In FIG. 1, the front-rear direction X and the vertical direction Z of the forklift 1 are indicated by arrows.

[0015] As shown in FIG. 1, the forklift 1 is a manned forklift that is operated by an operator M riding on the forklift 1. The forklift 1 includes a vehicle body 11, a lift lever 12, forks 13, and a lift device 20.

[0016] The vehicle body 11 is equipped with a motor 11A, which is a rotary electric motor, as a prime mover for traveling. The vehicle body 11 travels on the road surface using the motor 11A as a power source. Note that, as a prime mover for traveling, an internal combustion engine may be provided instead of (or in addition to) the motor 11A.

[0017] The lift lever 12 is an operation unit operated by the operator M and is operated to control the opening degree of a lift control valve 34 (see FIG. 2) described later. The lift lever 12 assumes a neutral state for maintaining the elevation of the forks 13, a non-neutral state for raising the forks 13, and a non-neutral state for lowering the forks 13. The lift lever 12 is configured to be tiltable in the front-rear direction X. When tilted backward from the neutral state, it switches to the non-neutral state for raising, and when tilted forward from the neutral state, it switches to the non-neutral state for lowering. When the operator M releases his or her hand from the non-neutral state lift lever 12 (that is, when no external force acts on the lift lever 12), the lift lever 12 is configured to automatically return to the neutral state. The lift lever 12 is configured to be interlocked with the valve body of the lift control valve 34 (see FIG. 2) described later, and the opening degree of the lift control valve 34 changes according to the operation of the lift lever 12.

[0018] The forks 13 are a pair of left and right claws and constitute a load support portion for supporting a load. The forks 13 are attached to a lift bracket 22 described later and are configured to be movable in the vertical direction Z together with the lift bracket 22.

[0019] The lift device 20 is a hydraulic device for raising and lowering the fork 13. The lift device 20 is composed of a mast 21, a lift bracket 22, a lift cylinder 23, etc. The lift cylinder 23 is an actuator that expands and contracts by hydraulic pressure, expands and contracts the mast 21 in the vertical direction Z, and moves the lift bracket 22 along the mast 21. In this way, the lift cylinder 23 moves the fork 13 in the vertical direction Z (i.e., raises and lowers it) with respect to the vehicle body 11.

[0020] As shown in FIG. 2, the lift cylinder 23 is a single-acting hydraulic cylinder, and has a hydraulic chamber 23A, a piston 23B that moves in the vertical direction Z according to the hydraulic pressure in the hydraulic chamber 23A, and a rod 23C that moves together with the piston 23B. When hydraulic oil is supplied to the hydraulic chamber 23A, the piston 23B and the rod 23C move upward, the mast 21 connected to the rod 23C extends, and the fork 13 rises together with the lift bracket 22. Also, when the hydraulic oil is discharged from the hydraulic chamber 23A, the piston 23B and the rod 23C move downward, the mast 21 contracts, and the fork 13 descends together with the lift bracket 22.

[0021] The hydraulic pressure in the lift cylinder 23 is higher when the fork 13 is supporting a load than when it is not, and the greater the weight of the load, the higher the hydraulic pressure, in a state where the fork 13 is stationary. Also, the lift cylinder 23 is configured such that when the fork 13 is in contact with the ground, the hydraulic pressure is lower due to the resistance force acting from the ground than when the fork 13 is not in contact with the ground.

[0022] Also, as shown in FIG. 2, the forklift 1 includes a tank 31, a pump 32, a motor 33, a lift control valve 34, a check valve 35, a lever sensor 41, a motor sensor 42, a hydraulic pressure sensor 43, a key switch 44, an audio playback device 45, and a control device 50.

[0023] The tank 31 is an oil tank that stores hydraulic oil, and the pump 32 is an oil delivery device that sends out hydraulic oil. The pump 32 sucks in hydraulic oil from the tank 31 and sends the hydraulic oil to the lift cylinder 23 via the lift control valve 34.

[0024] The motor 33 is a rotary electric motor equipped with a rotor 33A and constitutes a pump drive unit that drives the pump 32. The motor 33 drives the pump 32 connected to the rotor 33A by rotating the rotor 33A. In this way, an electric oil pump is constituted by the pump 32 and the motor 33.

[0025] The lift control valve 34 is a manual valve provided with a spool (not shown) which is a valve body interlocked with the lift lever 12, and is a three-port valve connected to the oil passages 34P, 34T, and 34C. The oil passage 34P is a flow path of the hydraulic oil flowing from the pump 32 to the lift control valve 34, the oil passage 34T is a flow path of the hydraulic oil flowing from the lift control valve 34 to the tank 31, and the oil passage 34C is a flow path of the hydraulic oil flowing from one of the lift control valve 34 and the lift cylinder 23 to the other. The lift control valve 34 controls the flow direction of the hydraulic oil by changing the connection mode of the oil passages 34P, 34T, and 34C according to the state of the lift lever 12, and controls the flow rate of the hydraulic oil by changing the opening degree (the position of the spool) according to the operation amount of the lift lever 12.

[0026] Specifically, when the lift lever 12 is in the neutral state, the lift control valve 34 closes the oil passages 34P, 34T, and 34C. In this case, the hydraulic oil sent out from the pump 32 is not supplied to the hydraulic chamber 23A of the lift cylinder 23, and the hydraulic oil in the hydraulic chamber 23A is not discharged to the tank 31.

[0027] Also, when the lift lever 12 is in the upward non-neutral state, the lift control valve 34 connects the oil passages 34P and 34C to each other and closes the oil passage 34T. In this case, the hydraulic oil sent out from the pump 32 is supplied to the hydraulic chamber 23A of the lift cylinder 23 through the oil passage 34P and the oil passage 34C. Also, at this time, the lift control valve 34 increases [or decreases] the flow rate of the hydraulic oil supplied to the hydraulic chamber 23A of the lift cylinder 23 by increasing [or decreasing] the opening degree.

[0028] Also, when the lift lever 12 is in the downward non-neutral state, the lift control valve 34 connects the oil passages 34T and 34C to each other and closes the oil passage 34P. In this case, the hydraulic oil in the hydraulic chamber 23A of the lift cylinder 23 is discharged to the tank 31 through the oil passage 34C and the oil passage 34T. Also, at this time, the lift control valve 34 increases [or decreases] the flow rate of the hydraulic oil discharged from the hydraulic chamber 23A of the lift cylinder 23 by increasing [or decreasing] the opening degree.

[0029] The check valve 35 is a check valve provided between the pump 32 and the lift control valve 34. The check valve 35 allows the flow of hydraulic oil from the pump 32 to the lift control valve 34 and prohibits the flow of hydraulic oil from the lift control valve 34 to the pump 32.

[0030] The lever sensor 41 detects the operation amount of the lift lever 12 and outputs the detection result to the control device 50. The lever sensor 41, together with a valve opening degree calculation unit 53 described later, constitutes a valve opening degree detection unit 61 (see FIG. 3) that detects the opening degree of the lift control valve 34.

[0031] The motor sensor 42 detects the rotation of the rotor 33A and outputs the detection result to the control device 50. The motor sensor 42, together with a rotation speed calculation unit 52 described later, constitutes a rotation speed detection unit 62 (see FIG. 3) that detects the rotation speed of the motor 33.

[0032] The hydraulic pressure sensor 43 constitutes a hydraulic pressure detection unit that detects the hydraulic pressure in the lift cylinder 23 by detecting the pressure of the hydraulic oil supplied to the hydraulic chamber 23A of the lift cylinder 23. The hydraulic pressure sensor 43 outputs the detection result of the hydraulic pressure in the lift cylinder 23 to the control device 50.

[0033] The key switch 44 opens and closes a circuit connected to the power supply (not shown) of the forklift 1. The key switch 44 is configured to be switchable between a key-on state and a key-off state using a key (not shown) inserted into the key switch 44. The key-on state is a state in which the key switch 44 closes the circuit in order to activate the traveling function for the vehicle body 11 to travel, the lifting function for the lifting device 20 to raise and lower the fork 13, and other predetermined functions. Also, the key-off state is a state in which the key switch 44 opens the circuit in order to deactivate the traveling function and the lifting function, etc. Note that not all functions are deactivated in the key-off state. For example, power is supplied to the audio playback device 45 and the control device 50 even in the key-off state so that the audio playback device 45 can notify of the mistake of forgetting to lower the fork 13.

[0034] The audio playback device 45 is composed of a memory that stores audio data and a speaker that outputs the audio data as audio. The audio playback device 45 constitutes a notification unit that notifies that the load acting on the fork 13 is an excessive load and that the fork 13 is not grounded to the ground. For example, the audio playback device 45 notifies that the load acting on the fork 13 is an excessive load by outputting an audio such as "Load over", and notifies that the fork 13 is not grounded to the ground by outputting an audio such as "Have you forgotten to lower the claws?".

[0035] The control device 50 is composed of an arithmetic processing unit that operates according to a predetermined program, and controls the motor 33 based on the state and operation amount of the lift lever 12. Specifically, when the lift lever 12 is in the upward non-neutral state based on the output of the lever sensor 41, the control device 50 controls the motor 33 so that the supply amount of the hydraulic oil by the pump 32 increases [or decreases] when the operation amount of the lift lever 12 becomes large [or small]. Further, the control device 50 executes a load measurement process, an excessive load notification / upward control process, and a forgetting-to-lower notification process, which will be described later.

[0036] As shown in FIG. 3, in order to execute a load measurement process, an excessive load notification / upward control process, and a forgetting-to-lower notification process, which will be described later, the control device 50 includes a load calculation unit 51, a rotational speed calculation unit 52, a valve opening calculation unit 53, a correction amount calculation unit 54, a load correction unit 55, a notification control unit 56, and a motor control unit 57.

[0037] The load calculation unit 51 calculates the load acting on the fork 13 (specifically, the load value representing the load acting on the fork 13) based on the hydraulic pressure detected by the hydraulic pressure sensor 43 (that is, the hydraulic pressure in the lift cylinder 23). When the fork 13 is moving up and down, the load calculated by the load calculation unit 51 includes the influence of the operating pressure (that is, the pressure change generated when the lift cylinder 23 operates). When the load acting on the fork 13 in the state where the fork 13 supports the load without touching the ground is set as a positive value, the influence of the operating pressure generated during the upward movement of the fork 13 can be represented by a force that increases the load compared to when the fork 13 is stopped (that is, a positive value force), and the influence of the operating pressure generated during the downward movement of the fork 13 can be represented by a force that decreases the load compared to when the fork 13 is stopped (that is, a negative value force). The magnitude of the influence of the operating pressure is correlated with the operation of the lift cylinder 23.

[0038] The rotational speed calculation unit 52 constitutes a rotational speed detection unit 62 that detects the rotational speed of the motor 33, and calculates the rotational speed (number of rotations per predetermined time) of the motor 33 based on the rotation of the rotor 33A detected by the motor sensor 42.

[0039] The valve opening calculation unit 53 constitutes a valve opening detection unit 61 that detects the opening of the lift control valve 34, and calculates the opening of the lift control valve 34 based on the operation amount of the lift lever 12 detected by the lever sensor 41.

[0040] The correction amount calculation unit 54 calculates a correction amount for correcting the load based on the opening detected by the valve opening detection unit 61 (i.e., calculated by the valve opening calculation unit 53) and the rotational speed detected by the rotational speed detection unit 62 (i.e., calculated by the rotational speed calculation unit 52).

[0041] Specifically, when the fork 13 is rising, the correction amount calculation unit 54 calculates an upward correction amount as a correction amount for correcting the load based on the opening of the lift control valve 34 calculated by the valve opening calculation unit 53 and the rotational speed of the motor 33 calculated by the rotational speed calculation unit 52.

[0042] The correction amount calculation unit 54, for example, when the upward correction amount is "α U ", the opening of the lift control valve 34 is "V", and the rotational speed of the motor 33 is "R", the upward correction amount can be calculated according to the mathematical formula "α U = A × V × R". In the above relational expression, "A" is a preset constant, which can be obtained by conducting an experiment to raise the fork 13 that supports a load with a known weight. Instead of calculating the upward correction amount according to the mathematical formula, the upward correction amount may be calculated by referring to a look-up table with the opening of the lift control valve 34 and the rotational speed of the motor 33 as input values and the upward correction amount as the output value.

[0043] In addition, when the fork 13 is descending, the correction amount calculation unit 54 calculates a descent correction amount as a correction amount for correcting the load based on the opening of the lift control valve 34 calculated by the valve opening calculation unit 53.

[0044] The correction amount calculation unit 54 calculates, for example, the descending correction amount as “α D ', and when the opening degree of the lift control valve 34 is 'V', 'α D =B×V". In the above relational expression, "B" is a preset constant, which can be obtained by conducting an experiment in which the forks 13 supporting a load of known weight are lowered. Note that instead of calculating the lowering correction amount according to the formula, the lowering correction amount may be calculated by referring to a lookup table in which the opening of the lift control valve 34 is used as an input value and the lowering correction amount is used as an output value.

[0045] In this embodiment, the correction amount calculation unit 54 calculates the upward correction amount as a positive value and calculates the downward correction amount as a negative value. Note that the correction amount calculation unit 54 may be configured to calculate the upward correction amount as a negative value and calculate the downward correction amount as a positive value.

[0046] In addition, when the forks 13 are not ascending or descending (i.e., when the opening degree of the lift control valve 34 is 0), the correction amount calculation unit 54 calculates the correction amount to 0 so that the load does not change before and after the load correction described below.

[0047] The load correction unit 55 corrects the load based on the correction amount calculated by the correction amount calculation unit 54 in order to exclude the influence of the operating pressure generated during the lifting and lowering of the fork 13 from the load (i.e., the load value) calculated by the load calculation unit 51. Specifically, in the present embodiment, the load correction unit 55 corrects the load by subtracting the correction amount (the upward correction amount which is a positive value / the downward correction amount which is a negative value) from the load value. When the fork 13 is not in the process of lifting and lowering, since the correction amount is 0, the load does not change before and after the correction. Note that when the upward correction amount is calculated as a negative value and when the downward correction amount is calculated as a positive value, the load correction unit 55 may correct the load by adding the correction amount to the load value.

[0048] The notification control unit 56 compares the load after correction by the load correction unit 55 with the overload determination threshold value in the overload notification and upward control process described later, and controls the audio playback device 45 based on the comparison result. Specifically, when the load after correction (i.e., the load excluding the influence of the operating pressure) becomes larger than the overload determination threshold value, the notification control unit 56 controls the audio playback device 45 to notify that the load acting on the fork 13 is an overload.

[0049] Also, in the forgetting-to-lower notification process described later, the notification control unit 56 compares the load calculated by the load calculation unit 51 with the grounding determination threshold value, and controls the audio playback device 45 based on the comparison result. Specifically, when the load is equal to or greater than the grounding determination threshold value, the notification control unit 56 controls the audio playback device 45 to notify that the fork 13 is not grounded (i.e., forgetting to lower the fork 13).

[0050] The motor control unit 57 constitutes a pump control unit that controls the pump drive unit. In the overload notification and rising control process described later, the motor control unit 57 compares the corrected load by the load correction unit 55 with the overload determination threshold value, and controls the motor 33 based on the comparison result. Specifically, when the corrected load (that is, the load excluding the influence of the operating pressure) becomes larger than the overload determination threshold value, the motor control unit 57 controls the motor 33 so that the flow rate of the hydraulic oil sent by the pump 32 decreases.

[0051] <Load measurement process> Referring to FIG. 4, the flow of the load measurement process executed by the control device 50 will be described. This load measurement process is executed at any time during the raising and lowering and stopping of the fork 13.

[0052] First, the load calculation unit 51 calculates a load value representing the load acting on the fork 13 based on the hydraulic pressure detected by the hydraulic pressure sensor 43 (step S1).

[0053] In parallel with step S1, the rotation speed calculation unit 52 calculates the rotation speed of the motor 33 based on the rotation speed of the rotor 33A detected by the motor sensor 42 (step S2), and the valve opening calculation unit 53 calculates the opening of the lift control valve 34 based on the operation amount of the lift lever 12 detected by the lever sensor 41 (step S3).

[0054] After steps S2 and S3, the correction amount calculation unit 54 determines whether the fork 13 is rising based on the opening calculated in step S3 (step S4). Further, when the correction amount calculation unit 54 determines that the fork 13 is not rising (step S4: NO), it determines whether the fork 13 is descending (step S5).

[0055] When the correction amount calculation unit 54 determines that the fork 13 is rising (step S4: YES), it calculates a positive rising correction amount based on the rotation speed calculated in step S2 and the opening calculated in step S3 (step S6). The rising correction amount is, for example, the above-mentioned "α"U It is calculated according to the formula "=A×V×R". Thus, in step S6, the correction amount calculation unit 54 sets the calculated upward correction amount as the correction amount to be used in step S9 described later.

[0056] On the other hand, when the correction amount calculation unit 54 determines that the fork 13 is descending (step S5: YES), it calculates a negative downward correction amount based on the opening calculated in step S3 (step S7). The downward correction amount is, for example, the above-mentioned "α D =B×V". Thus, in step S7, the correction amount calculation unit 54 sets the calculated downward correction amount as the correction amount to be used in step S9 described later.

[0057] Also, when the correction amount calculation unit 54 determines that the fork 13 is neither ascending nor descending (step S5: NO), it sets 0 as the correction amount to be used in step S9 described later (step S8).

[0058] After step S1 and after steps S6 to S8, the load correction unit 55 corrects the load value calculated in step S1 based on the correction amount set in any of steps S6 to S8 (step S9). That is, in step S9, the load correction unit 55 calculates a load excluding the influence of the operating pressure by subtracting the correction amount from the load calculated based on the hydraulic pressure. When a positive upward correction amount is calculated in step S6, the load correction unit 55 corrects the load value so that the load value becomes smaller by subtracting the upward correction amount from the load value. When a negative downward correction amount is calculated in step S7, the load correction unit 55 corrects the load value so that the load value becomes larger by subtracting the downward correction amount from the load value. Thus, a load excluding the influence of the operating pressure is measured during the lifting and lowering of the fork 13.

[0059] <Overload Notification and Ascent Control Process> The overload notification and ascent control process will be described. This overload notification and ascent control process is executed when the fork 13 is ascending to lift a load.

[0060] When the fork 13 is rising, the notification control unit 56 determines whether the load measured by the above-described load measurement process (that is, the corrected load value in step S7) is greater than a predetermined excessive load determination threshold value. When the notification control unit 56 determines that the load is greater than the excessive load determination threshold value, the notification control unit 56 controls the audio playback device 45 to notify that the load acting on the fork 13 is an excessive load. Thus, when the fork 13 is rising and the corrected load is greater than the predetermined excessive load determination threshold value, the notification control unit 56 operates the audio playback device 45.

[0061] Also, when the fork 13 is rising, the motor control unit 57 determines whether the load measured by the above-described load measurement process (that is, the corrected load value in step S7) is greater than the excessive load determination threshold value. When the motor control unit 57 determines that the load is greater than the excessive load determination threshold value, the motor control unit 57 controls the motor 33 so that the flow rate of the hydraulic oil sent by the pump 32 decreases. Thus, when the fork 13 is rising and the corrected load is greater than the overloading determination threshold value, the motor control unit 57 controls the motor 33 to limit the rising of the fork 13.

[0062] <Forgot to Lower Notification Process> Referring to FIG. 5, the flow of the forgot to lower notification process will be described. First, the notification control unit 56 determines whether the key switch 44 has been switched from the key-on state to the key-off state (step S11). If the key switch 44 maintains the key-on state (step S11: NO), the process does not proceed to the following step S12.

[0063] When the key switch 44 is switched from the key-on state to the key-off state (step S11: YES), similar to step S1, the load calculation unit 51 calculates a load value representing the load acting on the fork 13 based on the output of the hydraulic pressure sensor 43 (step S12). Note that since step S12 is after the switch to the key-off state, the fork 13 is not moving up and down. Therefore, since the correction amount for the load calculated in step S12 is 0, the load value does not change before and after correction by the load correction unit 55.

[0064] Next, the notification control unit 56 determines whether the fork 13 is in contact with the ground based on the load value calculated in step S12 (step S13). Specifically, in step S13, the notification control unit 56 determines that the fork 13 is in contact with the ground when the load value is less than the ground contact determination threshold, and determines that the fork 13 is not in contact with the ground when the load value is greater than or equal to the ground contact determination threshold. When the notification control unit 56 determines that the fork 13 is in contact with the ground (step S13: YES), it does not proceed to the following step S14 and ends the forgetting-to-lower notification process.

[0065] When the notification control unit 56 determines that the fork 13 is not in contact with the ground (step S13: NO), it controls the voice playback device 45 to notify of the forgetting to lower the fork 13 (step S14). Thus, the notification control unit 56 operates the voice playback device 45 when the key switch 44 is in the key-off state (step S1: YES) and the load is greater than or equal to a predetermined ground contact determination threshold (step S13: NO).

[0066] The following effects can be obtained in this embodiment. (1) The forklift 1 (a material handling vehicle) includes a load calculation unit 51 that calculates a load based on hydraulic pressure, a correction amount calculation unit 54 that calculates a correction amount based on the opening degree of the lift control valve 34, and a load correction unit 55 that corrects the load based on the correction amount. According to this configuration, the load calculated based on the hydraulic pressure in the lift cylinder 23 is corrected by the correction amount calculated based on the opening degree of the lift control valve 34. Since the opening degree of the lift control valve 34 is related to the flow rate of the hydraulic oil sent to the lift cylinder 23, it is a parameter related to the operation of the lift cylinder 23. Therefore, the load can be corrected according to the pressure change generated when the lift cylinder 23 operates, that is, the operating pressure, and the load acting on the fork 13 can be measured by excluding the influence of the operating pressure generated during the lifting and lowering of the fork 13.

[0067] (2) The forklift 1 is provided with a rotational speed detection unit 62 that detects the rotational speed of the motor 33 (pump drive unit), and the correction amount calculation unit 54 calculates the above correction amount based on the opening degree of the lift control valve 34 and the rotational speed of the motor 33. Since the rotational speed of the motor 33 is related to the flow rate of the hydraulic oil sent to the lift cylinder 23, similar to the opening degree of the lift control valve 34, it is a parameter related to the operation of the lift cylinder 23. Therefore, the load can be corrected more appropriately according to the operating pressure, and the load acting on the fork 13 can be accurately measured by precisely excluding the influence of the operating pressure generated during the lifting and lowering of the fork 13.

[0068] (3) The valve opening degree detection unit 61 is composed of a lever sensor 41 that detects the operation amount of the lift lever 12 and a valve opening degree calculation unit 53 that calculates the opening degree of the lift control valve 34 based on the detected operation amount. According to this configuration, the opening degree of the lift control valve 34 that operates in response to the operation of the lift lever 12 can be indirectly detected using the lever sensor 41.

[0069] (4) When the fork 13 is rising and the corrected load based on the correction amount becomes greater than a predetermined excessive load determination threshold, the notification control unit 56 operates the audio playback device 45 (notification unit). According to this configuration, immediately after the fork 13 has lifted the load, that is, before the lifted fork 13 stops, it is possible to notify that the weight of the load is excessive.

[0070] (5) When the fork 13 is rising and the corrected load based on the correction amount becomes greater than a predetermined excessive load determination threshold, the motor control unit 57 (pump control unit) controls the motor 33 to limit the rising of the fork 13. According to this configuration, immediately after the fork 13 has lifted the load, the rising of the fork 13 is restricted, so the safety of the forklift 1 can be further enhanced.

[0071] (6) When the key switch 44 is in the key-off state and the load acting on the fork 13 is equal to or greater than a predetermined ground contact determination threshold, the notification control unit 56 operates the audio playback device 45. According to this configuration, it is possible to notify that the fork 13 is not in contact with the ground, that is, the fork 13 has been forgotten to be lowered.

[0072] The present invention is not limited to the above-described embodiments, and the above configuration can also be changed. For example, it can be implemented by changing as follows, or can be implemented by combining the following changes.

[0073] · The forklift 1 may be provided with a display, a buzzer, a stack signal lamp, or a combination thereof that functions as a notification unit instead of or in addition to the audio playback device 45. That is, the configuration of the notification unit may be appropriately changed.

[0074] · If the rotational speed of the motor 33 is constant when the fork 13 is rising, the correction amount calculation unit 54 may be configured to calculate the correction amount based on the opening degree of the lift control valve 34 without using the rotational speed of the motor 33. Also, the mathematical formula for calculating the correction amount may be appropriately changed.

[0075] · The forklift 1 is provided with an oil temperature sensor (not shown) that detects the temperature of the hydraulic oil (i.e., the oil temperature), and the correction amount calculation unit 54 may calculate the correction amount based on the temperature detected by the oil temperature sensor in addition to the opening degree of the lift control valve 34. Also, the correction amount calculation unit 54 may calculate the correction amount based on the temperature detected by the oil temperature sensor in addition to the opening degree of the lift control valve 34 and the rotational speed of the motor 33. According to this configuration, the influence of the operating pressure generated during the lifting and lowering of the fork 13 can be more accurately excluded, and the load acting on the fork 13 can be measured more accurately.

[0076] · The valve opening degree detection unit 61 may be configured by a sensor other than the lever sensor 41 (for example, a displacement sensor that detects the position of the spool of the lift control valve 34). That is, the configuration of the valve opening degree detection unit 61 may be appropriately changed.

[0077] · If it is operated to operate the lift cylinder 23, the operation unit may be configured by an input device other than the lift lever 12. Also, the forklift 1 may be an unmanned forklift that automatically travels and performs cargo handling.

[0078] · The lift cylinder 23 may be a double-acting hydraulic cylinder. In this case, when the fork 13 is descending, it is preferable that the correction amount calculation unit 54 calculates the correction amount based on the rotation speed of the motor 33 and the opening degree of the lift control valve 34. Further, in this case, it is preferable that during the descent of the fork 13, the motor control unit 57 controls the motor 33 based on the corrected load based on the correction amount. Specifically, for example, when the fork 13 is descending and the corrected load based on the correction amount becomes smaller than a predetermined load placement determination threshold value, it is preferable that the motor control unit 57 determines that the fork 13 has placed a load and controls the motor 33 to limit the descent of the fork 13.

[0079] · Instead of the motor 11A, an engine 11B (see FIG. 6), which is an internal combustion engine as a driving source for traveling, may be mounted on the vehicle body 11, and the vehicle body 11 may travel on the road surface using the engine 11B as a power source. Further, in this configuration, the engine 11B may be configured to drive the pump 32. The configuration of the forklift 1 according to this modification will be described with reference to FIGS. 6 and 7.

[0080] As shown in FIG. 6, the forklift 1 according to the modification includes an engine 11B instead of the motor 33 (see FIG. 2) and an engine sensor 42' instead of the motor sensor 42 (see FIG. 2).

[0081] The engine 11B constitutes a wheel drive unit that drives the wheels and a pump drive unit that drives the pump 32. That is, the output of the engine 11B is configured to be distributed to the wheels and the pump 32.

[0082] The engine sensor 42' detects the rotation of the engine shaft of the engine 11B and outputs the detection result to the control device 50. The engine sensor 42' constitutes a rotation speed detection unit 62' (see FIG. 7) that detects the rotation speed of the engine 11B together with the rotation speed calculation unit 52.

[0083] As shown in FIG. 7, the control device 50 of this modified example includes an engine control unit 57' instead of the motor control unit 57 (see FIG. 3), and controls the engine 11B instead of the motor 33 based on the state and operation amount of the lift lever 12 (see FIG. 6).

[0084] The rotation speed calculation unit 52 of this modified example constitutes a rotation speed detection unit 62' that detects the rotation speed of the engine 11B, and calculates the rotation speed of the engine 11B based on the rotation of the engine shaft detected by the engine sensor 42'. Further, the correction amount calculation unit 54 of this modified example calculates the correction amount based on the rotation speed of the engine 11B instead of the rotation speed of the motor 33.

[0085] The engine control unit 57' constitutes a control unit for the pump, and in the overload notification and rising control process, compares the load after correction by the load correction unit 55 with the overload determination threshold value, and controls the engine 11B based on the comparison result.

[0086] Since the rotation speed of the engine 11B is related to the flow rate of the hydraulic oil sent to the lift cylinder 23, similar to the opening degree of the lift control valve 34, it is a parameter related to the operation of the lift cylinder 23. Therefore, even in the modified examples shown in FIGS. 6 and 7, the effects described in the above embodiment can be obtained.

[0087] · The configuration of the present invention is not limited to the forklift 1 equipped with the fork 13, and may be applied to other cargo handling vehicles equipped with a load support portion. For example, the configuration of the present invention may be applied to a clamp lift truck equipped with a clamp device instead of the fork 13, or a container handler that holds a container.

Description of Reference Numerals

[0088] 1 Forklift (Cargo Handling Vehicle) 11A Motor 11B Engine (Pump Driving Unit) 12 Lift Lever 13 Fork (Load Support Portion) 23 Lift Cylinder 32 Pump 33 Motor (pump drive unit) 34 Lift control valve 41 Lever sensor 42 Motor sensor 42’ Engine sensor 43 Hydraulic sensor (hydraulic detection unit) 44 Key switch 45 Audio playback device (notification unit) 51 Load calculation unit 52 Rotational speed calculation unit 53 Valve opening calculation unit 54 Correction amount calculation unit 55 Load correction unit 56 Notification control unit 57 Motor control unit (pump control unit) 57’ Engine control unit (pump control unit) 61 Valve opening detection unit 62,62’ Rotational speed detection unit

Claims

1. A luggage support portion for supporting luggage; A lift cylinder that raises and lowers the luggage support portion; A pump for supplying hydraulic fluid to the lift cylinder; A pump driving unit that drives the pump; a lift control valve for controlling a flow rate of the hydraulic oil; a valve opening detection unit that detects an opening of the lift control valve; A hydraulic pressure detection unit that detects hydraulic pressure in the lift cylinder; a load calculation unit that calculates a load acting on the luggage support unit based on the hydraulic pressure; a correction amount calculation unit that calculates a correction amount for correcting the load based on the opening degree; and a load correction unit that corrects the load based on the correction amount. A loading vehicle characterized by:

2. a rotation speed detection unit that detects the rotation speed of the pump drive unit, The correction amount calculation unit calculates the correction amount based on the opening degree and the rotation speed.

2. The loading vehicle according to claim 1 .

3. A lift lever is provided which is operated to control the opening degree, The valve opening detection unit includes a lever sensor that detects an amount of operation of the lift lever, and a valve opening calculation unit that calculates the opening based on the amount of operation.

3. The loading vehicle according to claim 1 or 2.

4. a notification unit that notifies that the load is an excessive load; A notification control unit that controls the notification unit, The notification control unit operates the notification unit when the luggage support unit is rising and when the load corrected based on the correction amount becomes larger than a predetermined excessive load determination threshold value.

3. The loading vehicle according to claim 1 or 2.

5. A pump control unit for controlling the pump drive unit, The pump control unit controls the pump drive unit to limit the ascent of the luggage support unit when the luggage support unit is ascending and when the load corrected based on the correction amount becomes larger than a predetermined excessive load determination threshold value.

3. The loading vehicle according to claim 1 or 2.

6. A fork as the luggage support portion; A key switch configured to be switchable between a key-on state and a key-off state; An alarm unit that notifies that the fork is not in contact with the ground; A notification control unit that controls the notification unit, The lift cylinder is configured such that the hydraulic pressure is lower when the forks are in contact with the ground than when the forks are not in contact with the ground, The notification control unit operates the notification unit when the key switch is in the key-off state and the load is equal to or greater than a predetermined ground contact determination threshold.

3. The loading vehicle according to claim 1 or 2.

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