JP2018193209A - Industrial vehicle - Google Patents

Abstract

To provide an industrial vehicle capable of reducing wasteful energy loss.SOLUTION: A forklift 1 includes an electromagnetic proportional relief valve 17 which is opened when the pressure between a hydraulic pump 10 and a tilt cylinder 7 reaches the relief pressure, a pressure sensor 20 detecting a cargo handling load of a cargo handling device 2, a relief pressure setting part 24 for setting a relief pressure based on a cargo handling load of the cargo handling device 2 detected by the pressure sensor 20, and a relief valve control part 25 for controlling the electromagnetic proportional relief valve 17 in accordance with the relief pressure set by the relief pressure setting part 24. The larger the cargo handling load of the load handling device 2 is, the higher the relief pressure setting part 24 sets the relief pressure.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an industrial vehicle.

  For example, a forklift described in Patent Document 1 is known as an industrial vehicle. The forklift described in Patent Document 1 includes a hydraulic pump driven by an engine, a hydraulic cylinder for cargo handling that is operated by hydraulic oil discharged from the hydraulic pump, and an oil that is disposed between the hydraulic pump and the hydraulic cylinder for cargo handling. And a control valve. The oil control valve has a valve spool for switching the flow direction of the hydraulic oil and a relief valve for controlling the pressure in the circuit. When the hydraulic cylinder for cargo handling reaches the stroke end during the operation of the hydraulic cylinder for cargo handling, the pressure in the high pressure circuit between the hydraulic pump and the oil control valve rises, and the pressure in the high pressure circuit rises to the relief valve When the set pressure is reached, the relief valve opens and hydraulic oil escapes to the tank.

JP-A-4-308199

  However, the following problems exist in the prior art. That is, when the cargo handling hydraulic cylinder reaches the stroke end, the relief valve operates. At this time, when the cargo handling load (load) is small, an unnecessary pressure applied to the hydraulic pump increases. For this reason, the load applied to the engine is increased, and energy is lost wastefully.

  The objective of this invention is providing the industrial vehicle which can reduce the loss of useless energy.

  One aspect of the present invention is an industrial vehicle including a hydraulic pump driven by a prime mover and a cargo handling device having a plurality of cargo handling hydraulic cylinders operated by hydraulic oil discharged from the hydraulic pump. An electromagnetic relief valve that opens when the pressure between the hydraulic cylinders reaches the relief pressure, a load detection unit that detects the cargo handling load of the cargo handling device, and a relief pressure based on the cargo handling load of the cargo handling device detected by the load detection unit. A relief pressure setting unit to be set, and a relief valve control unit to control the electromagnetic relief valve in accordance with the relief pressure set by the relief pressure setting unit. The pressure is set high.

  In such an industrial vehicle, the electromagnetic relief valve opens when the pressure between the hydraulic pump and the cargo handling hydraulic cylinder reaches the relief pressure of the electromagnetic relief valve by the cargo handling hydraulic cylinder reaching the stroke end. At this time, the relief pressure of the electromagnetic relief valve is set higher as the cargo handling load of the cargo handling apparatus is larger. Therefore, when the cargo handling load of the cargo handling device is small, the relief pressure of the electromagnetic relief valve becomes low. For this reason, the unnecessary pressure applied to the hydraulic pump is reduced before the electromagnetic relief valve is opened. Thereby, since the load concerning a motor | power_engine is reduced, the loss of useless energy is reduced. Further, when the cargo handling load of the cargo handling device is large, the relief pressure of the electromagnetic relief valve becomes high. As a result, the electromagnetic relief valve is prevented from opening immediately, so that it is possible to prevent the operation of the cargo handling hydraulic cylinder from being stopped and the cargo handling from being stopped.

  The cargo handling device includes a mast and a fork attached to the mast and loads a load. One of the plurality of hydraulic cylinders for cargo handling is a lift cylinder that lifts and lowers the fork, and an electromagnetic relief valve includes a hydraulic pump and It opens when the pressure between the hydraulic cylinders other than the lift cylinder among the multiple hydraulic cylinders reaches the relief pressure, and the load detector detects the pressure of the lift cylinder as the cargo handling load of the cargo handling device. The setting unit may set the relief pressure higher as the pressure of the lift cylinder is higher.

  In such a configuration, when operating the hydraulic cylinder for cargo handling other than the lift cylinder, loss of useless energy is reduced, and the operation of the hydraulic cylinder for cargo handling is stopped and the cargo handling is not performed. Is done. In addition, since an existing pressure sensor that detects the pressure of the lift cylinder can be used as the load detection unit, it is not necessary to separately install a special sensor that detects the loading load of the loading apparatus on the industrial vehicle.

  Another one of the plurality of hydraulic cylinders for cargo handling is a tilt cylinder that tilts the mast back and forth, and the electromagnetic relief valve may be opened when the pressure between the hydraulic pump and the tilt cylinder reaches the relief pressure.

  When the mast is tilted backward by the tilt cylinder, the tilt cylinder easily reaches the stroke end. Therefore, it is particularly effective to use an electromagnetic relief valve that opens when the pressure between the hydraulic pump and the tilt cylinder reaches the relief pressure.

  The relief pressure setting unit sets the relief pressure to the first pressure when the cargo handling load of the cargo handling device is below the reference value, and sets the relief pressure to the first pressure when the cargo handling load of the cargo handling device is larger than the reference value. A higher second pressure may be set.

  In such a configuration, the relief pressure of the electromagnetic relief valve is set to either the first pressure or the second pressure in accordance with the cargo handling load of the cargo handling device, so that the processing procedure by the relief pressure setting unit can be simplified.

  According to the present invention, useless energy loss can be reduced.

It is a lineblock diagram showing roughly a forklift as one embodiment of an industrial vehicle concerning the present invention. It is a flowchart which shows the detail of the setting process procedure of the tilt relief pressure performed by the relief pressure setting part. As a comparative example, when the tilt relief pressure of the electromagnetic proportional relief valve is a constant value, it is a graph showing a state when the mast is tilted backward by a tilt cylinder. It is a graph which shows the state when a mast is tilted backward by a tilt cylinder when changing the tilt relief pressure of an electromagnetic proportional relief valve according to the cargo handling load of a cargo handling apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram schematically showing a forklift as an embodiment of an industrial vehicle according to the present invention. In FIG. 1, a forklift 1 that is an industrial vehicle of this embodiment includes a cargo handling device 2.

  The cargo handling device 2 has a mast 3. The mast 3 includes an outer mast 3a supported to be tiltable by a vehicle body (not shown), and an inner mast 3b disposed inside the outer mast 3a and capable of moving up and down with respect to the outer mast 3a. . A fork 4 on which a load is loaded is supported on the inner mast 3b through a lift bracket 5 so as to be lifted and lowered.

  In addition, the cargo handling device 2 includes a lift cylinder 6 that moves the fork 4 up and down, and a tilt cylinder 7 that tilts the mast 3 back and forth. The lift cylinder 6 and the tilt cylinder 7 constitute a plurality of hydraulic cylinders for cargo handling. The tilt cylinder 7 is a cargo handling hydraulic cylinder other than the lift cylinder 6 among the plurality of cargo handling hydraulic cylinders.

  The tip of the piston rod 6a of the lift cylinder 6 is connected to the upper part of the inner mast 3b. A chain wheel 8 is attached to the upper part of the inner mast 3b. A chain (not shown) is hung on the chain wheel 8. One end of the chain is connected to the lift cylinder 6, and the other end of the chain is connected to the lift bracket 5. When the lift cylinder 6 is extended, the fork 4 is raised, and when the lift cylinder 6 is contracted, the fork 4 is lowered.

  The tip of the piston rod 7a of the tilt cylinder 7 is rotatably connected to the outer mast 3a. When the tilt cylinder 7 extends, the mast 3 tilts forward, and when the tilt cylinder 7 contracts, the mast 3 tilts backward.

  The forklift 1 includes a prime mover 9 that is a driving source for traveling operation and cargo handling operation, a hydraulic pump 10 that is driven by the prime mover 9 to discharge hydraulic oil, a tank 11 that stores hydraulic oil, and a hydraulic pump 10. An oil control valve 12 disposed between the cargo handling device 2, a lift operation lever 13 that performs an instruction operation for operating the lift cylinder 6, and a tilt operation lever that performs an instruction operation for operating the tilt cylinder 7. 14. The prime mover 9 is an engine or a motor.

  The oil control valve 12 includes a lift electromagnetic proportional control valve 15, a tilt electromagnetic proportional control valve 16, and an electromagnetic proportional relief valve 17.

  The lift electromagnetic proportional control valve 15 is disposed between the hydraulic pump 10 and the lift cylinder 6. The lift electromagnetic proportional control valve 15 controls the flow rate of hydraulic fluid supplied from the hydraulic pump 10 to the lift cylinder 6 by changing the opening degree in proportion to the control current value input to the solenoid unit. It is a valve.

  The tilt electromagnetic proportional control valve 16 is disposed between the hydraulic pump 10 and the tilt cylinder 7. The electromagnetic proportional control valve for tilt 16 controls the flow rate of the hydraulic oil supplied from the hydraulic pump 10 to the tilt cylinder 7 by changing the opening degree in proportion to the control current value input to the solenoid unit. It is a valve.

  The electromagnetic proportional relief valve 17 is a relief valve that opens when the pressure between the hydraulic pump 10 and the tilt cylinder 7 reaches the relief pressure. When the electromagnetic proportional relief valve 17 is opened, the hydraulic oil in the oil control valve 12 is discharged to the tank 11. In the electromagnetic proportional relief valve 17, the relief pressure changes in proportion to the control current value input to the solenoid unit.

  The forklift 1 includes a lift operation detection sensor 18, a tilt operation detection sensor 19, a pressure sensor 20, and a controller 21.

  The lift operation detection sensor 18 detects the operation state (operation direction and operation amount) of the lift operation lever 13. The tilt operation detection sensor 19 detects the operation state (operation direction and operation amount) of the tilt operation lever 14. The pressure sensor 20 is a load detection unit that detects the pressure of the lift cylinder 6 as a cargo handling load of the cargo handling device 2. At this time, the pressure sensor 20 detects the pressure in the bottom chamber of the lift cylinder 6.

  The controller 21 includes a lift control valve control unit 22, a tilt control valve control unit 23, a relief pressure setting unit 24, and a relief valve control unit 25.

  The lift control valve control unit 22 controls the lift electromagnetic proportional control valve 15 according to the operation state of the lift operation lever 13 detected by the lift operation detection sensor 18. Specifically, the lift control valve control unit 22 outputs a control current value corresponding to the operation amount of the lift operation lever 13 to the solenoid unit of the lift electromagnetic proportional control valve 15.

  Thereby, the fork 4 moves up and down. Specifically, when the lift operation lever 13 instructs to raise the fork 4, the hydraulic oil discharged from the hydraulic pump 10 is supplied to the bottom chamber of the lift cylinder 6 through the lift electromagnetic proportional control valve 15. As a result, the fork 4 rises. When the lowering operation of the fork 4 is instructed by the lift operation lever 13, the fork 4 is lowered by the weight of the fork 4 and the load, and the hydraulic oil from the bottom chamber of the lift cylinder 6 passes through the lift electromagnetic proportional control valve 15. Return to the tank 11.

  The tilt control valve control unit 23 controls the tilt electromagnetic proportional control valve 16 according to the operation state of the tilt operation lever 14 detected by the tilt operation detection sensor 19. Specifically, the tilt control valve control unit 23 outputs a control current value corresponding to the operation amount of the tilt operation lever 14 to the solenoid unit of the tilt electromagnetic proportional control valve 16.

  Thereby, the mast 3 tilts. Specifically, when the tilt operation lever 14 instructs the forward tilting operation of the mast 3, the hydraulic oil discharged from the hydraulic pump 10 passes through the tilt electromagnetic proportional control valve 16 and enters the bottom chamber of the tilt cylinder 7. By being supplied, the mast 3 tilts forward. When the tilting operation lever 14 instructs to tilt the mast 3 backward, the hydraulic oil discharged from the hydraulic pump 10 is supplied to the rod chamber of the tilt cylinder 7 through the tilt electromagnetic proportional control valve 16. The mast 3 tilts backward.

  The relief pressure setting unit 24 sets the relief pressure of the electromagnetic proportional relief valve 17 based on the pressure of the lift cylinder 6 detected by the pressure sensor 20. As described above, the electromagnetic proportional relief valve 17 opens when the pressure between the hydraulic pump 10 and the tilt cylinder 7 reaches the relief pressure.

  Here, when the load loaded on the fork 4 is lifted by the lift cylinder 6, a pressure for holding the load (lift holding pressure) is applied to the lift cylinder 6. Further, when the mast 3 is tilted backward by the tilt cylinder 7 in a state where the load is loaded on the fork 4, a pressure for holding the load (tilt holding pressure) is applied to the tilt cylinder 7. The lift cylinder 6 and the tilt cylinder 7 are connected via the mast 3. For this reason, there is a correlation between the lift holding pressure and the tilt holding pressure, although it depends on conditions such as the vehicle case and the dimensions of the mast 3. Therefore, it is possible to estimate the tilt holding pressure from the lift holding pressure without detecting the tilt holding pressure with a sensor. Therefore, the relief pressure setting unit 24 sets the relief pressure (tilt relief pressure) of the electromagnetic proportional relief valve 17 from the pressure of the lift cylinder 6.

  FIG. 2 is a flowchart showing details of the tilt relief pressure setting processing procedure executed by the relief pressure setting unit 24. In addition, this flowchart has shown the process sequence in case the backward inclination operation | movement of the mast 3 is implemented.

  In FIG. 2, the relief pressure setting unit 24 first determines whether or not the tilt operation lever 14 has instructed the backward tilting operation of the mast 3 (step S101). When the relief pressure setting unit 24 determines that the backward tilting operation of the mast 3 has been instructed, the relief pressure setting unit 24 acquires the detection value of the pressure sensor 20 (step S102).

  Subsequently, the relief pressure setting unit 24 determines whether or not the detection value of the pressure sensor 20 is equal to or less than a reference value (step S103). The reference value is determined in advance by experiment or calculation. The reference value is 4 MPa, for example.

  When the relief pressure setting unit 24 determines that the detected value of the pressure sensor 20 is equal to or less than the reference value, the relief pressure setting unit 24 sets the tilt relief pressure of the electromagnetic proportional relief valve 17 to the first pressure (step S104). The first pressure is, for example, 5 MPa.

  When the relief pressure setting unit 24 determines that the detected value of the pressure sensor 20 is not below the reference value, that is, the detected value of the pressure sensor 20 is greater than the reference value, the relief pressure setting unit 24 sets the tilt relief pressure of the electromagnetic proportional relief valve 17 to the second value. The pressure is set (step S105). The second pressure is a pressure higher than the first pressure, for example, 15 MPa.

  Through the above processing, the relief pressure setting unit 24 sets the tilt relief pressure of the electromagnetic proportional relief valve 17 higher as the pressure of the lift cylinder 6 is higher, that is, as the cargo handling load of the cargo handling device 2 is larger.

  The relief pressure setting unit 24 may execute the same processing as described above when the tilt operation lever 14 instructs the forward tilting operation of the mast 3, or may depend on the detection value of the pressure sensor 20. Instead, the tilt relief pressure of the electromagnetic proportional relief valve 17 may be set to a constant value.

  Returning to FIG. 1, the relief valve control unit 25 controls the electromagnetic proportional relief valve 17 in accordance with the tilt relief pressure set by the relief pressure setting unit 24. Specifically, the relief valve control unit 25 outputs a control current value corresponding to the tilt relief pressure to the solenoid unit of the electromagnetic proportional relief valve 17.

  As a result, when the pressure between the hydraulic pump 10 and the tilt cylinder 7 reaches the tilt relief pressure, the electromagnetic proportional relief valve 17 is opened, so that the hydraulic oil from the hydraulic pump 10 passes through the electromagnetic proportional relief valve 17 to the tank. 11 is discharged. That is, the electromagnetic proportional relief valve 17 is relieved.

  FIG. 3 is a graph showing a state when the mast 3 is tilted backward by the tilt cylinder 7 when the tilt relief pressure of the electromagnetic proportional relief valve 17 is a constant value as a comparative example. The horizontal axis of the graph represents time, and the vertical axis of the graph represents pressure. A solid line X in the graph indicates a pressure between the hydraulic pump 10 and the tilt cylinder 7 (hereinafter referred to as pump pressure). A one-dot chain line Y in the graph indicates the pressure of the lift cylinder 6 detected by the pressure sensor 20. Further, the tilt relief pressure of the electromagnetic proportional relief valve 17 is a predetermined value (for example, 15 MPa).

  FIG. 3 (a) shows a state when the cargo handling load of the cargo handling device 2 is small (low load), and FIG. 3 (b) shows a status when the cargo handling load of the cargo handling device 2 is large (high load). Show. In each figure, when the tilting cylinder 7 contracts at time t1 and the rearward tilting of the mast 3 is started, the pump pressure rises. At time t2, the pump pressure becomes a specified value corresponding to the cargo handling load. At this time, the specified value at the time of high load is larger than the specified value at the time of low load. At time t3, the tilt cylinder 7 reaches the rearward tilt side stroke end, and the pump pressure rises again. Thereafter, the pump pressure reaches the tilt relief pressure, and the electromagnetic proportional relief valve 17 is relieved.

  At this time, as shown in FIG. 3B, at a high load, the specified value of the pump pressure is high, and therefore the difference ΔP between the tilt relief pressure and the specified value of the pump pressure is small. For this reason, the pressure wastefully applied to the hydraulic pump 10 before the electromagnetic proportional relief valve 17 is relieved is low.

  However, as shown in FIG. 3A, at the time of low load, the specified value of the pump pressure is low, so that the difference ΔP between the tilt relief pressure and the specified value of the pump pressure becomes large. For this reason, the pressure which is wastedly applied to the hydraulic pump 10 until the electromagnetic proportional relief valve 17 is relieved increases. As a result, the load applied to the prime mover 9 is increased, and energy is wasted.

  FIG. 4 is a graph showing a state when the mast 3 is tilted backward by the tilt cylinder 7 when the tilt relief pressure of the electromagnetic proportional relief valve 17 is changed in accordance with the cargo handling load of the cargo handling device 2. FIG. 4 (a) shows a state when the cargo handling load of the cargo handling device 2 is small (low load), and FIG. 4 (b) shows a status when the cargo handling load of the cargo handling device 2 is large (high load). Show. The solid line X and the one-dot chain line Y are the same as those in FIG.

  As shown in FIG. 4A, at the time of low load, the tilt relief pressure of the electromagnetic proportional relief valve 17 is the first pressure (for example, 5 MPa). In this case, since the tilt relief pressure is lower than that in the comparative example shown in FIG. 3A, the difference ΔP between the tilt relief pressure and the specified value of the pump pressure is reduced. Accordingly, the pressure applied to the hydraulic pump 10 by the time the electromagnetic proportional relief valve 17 is relieved is reduced. Thereby, since the load concerning the prime mover 9 is reduced, loss of useless energy is reduced.

  Further, as shown in FIG. 4B, at the time of high load, the tilt relief pressure of the electromagnetic proportional relief valve 17 is a second pressure (for example, 15 MPa) higher than the first pressure. In this case, the electromagnetic proportional relief valve 17 is immediately relieved, so that the backward tilting operation of the mast 3 is prevented from being performed halfway.

  As described above, according to the present embodiment, when the tilt cylinder 7 reaches the stroke end and the pressure between the hydraulic pump 10 and the tilt cylinder 7 reaches the relief pressure of the electromagnetic proportional relief valve 17, the electromagnetic proportional The relief valve 17 opens. At this time, the relief pressure of the electromagnetic proportional relief valve 17 is set higher as the cargo handling load of the cargo handling apparatus 2 is larger.

  Therefore, when the cargo handling load of the cargo handling device 2 is small, the relief pressure of the electromagnetic proportional relief valve 17 becomes low. For this reason, the unnecessary pressure applied to the hydraulic pump 10 is lowered before the electromagnetic proportional relief valve 17 is opened. Thereby, since the load concerning the prime mover 9 is reduced, loss of useless energy is reduced. As a result, deterioration of fuel consumption can be suppressed. In addition, since the pressure applied to the hydraulic pump 10 and the tilt cylinder 7 is reduced before the electromagnetic proportional relief valve 17 is opened, the strength of the hydraulic pump 10 itself and the tilt cylinder 7 itself is extended, and the tilt cylinder 7 is connected. The strength life of the mast 3 is extended.

  On the other hand, when the cargo handling load of the cargo handling device 2 is large, the relief pressure of the electromagnetic proportional relief valve 17 becomes high. As a result, the electromagnetic proportional relief valve 17 is prevented from opening immediately, so that the operation of the tilt cylinder 7 is stopped in the middle and cargo handling is not performed.

  In addition, since the existing pressure sensor 20 that detects the pressure of the lift cylinder 6 can be used as a load detection unit, it is not necessary to separately mount a special sensor that detects the load on the cargo handling device 2 on the forklift 1.

  Further, when the mast 3 is tilted backward by the tilt cylinder 7, the tilt cylinder 7 easily reaches the stroke end. Therefore, it is particularly effective to use the electromagnetic proportional relief valve 17 that opens when the pressure between the hydraulic pump 10 and the tilt cylinder 7 reaches the relief pressure.

  Further, since the relief pressure of the electromagnetic proportional relief valve 17 is set to either the first pressure or the second pressure according to the cargo handling load of the cargo handling device 2, the processing procedure by the relief pressure setting unit 24 can be simplified.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, the relief pressure setting unit 24 sets the relief pressure of the electromagnetic proportional relief valve 17 to the first pressure when the pressure of the lift cylinder 6 is equal to or lower than the reference value, and the pressure of the lift cylinder 6 is When the pressure is not less than the reference value, the relief pressure of the electromagnetic proportional relief valve 17 is set to the second pressure higher than the first pressure, but the form is not particularly limited. The relief pressure setting unit 24 may set the relief pressure of the electromagnetic proportional relief valve 17 continuously or stepwise as the pressure in the lift cylinder 6 increases. At this time, the relief pressure setting unit 24 sets the relief pressure of the electromagnetic proportional relief valve 17 by a map or calculation. In short, the relief pressure setting unit 24 may set the relief pressure of the electromagnetic proportional relief valve 17 higher as the cargo handling load of the cargo handling device 2 is larger.

  In the above embodiment, the pressure sensor 20 detects the pressure of the lift cylinder 6 as the cargo handling load of the cargo handling device 2. However, the present invention is not limited to this configuration, and the pressure of the tilt cylinder 7 is the cargo handling load of the cargo handling device 2. You may detect as.

  Further, in the above embodiment, the forklift 1 includes the electromagnetic proportional relief valve 17 that opens when the pressure between the hydraulic pump 10 and the tilt cylinder 7 reaches the relief pressure, and the relief pressure setting unit 24 handles the cargo handling device 2. Although the relief pressure of the electromagnetic proportional relief valve 17 is set based on the load, it is not particularly limited to that form. For example, when the cargo handling device 2 has an attachment cylinder that operates an attachment such as a side shift fork or a hinged fork, the forklift 1 is an electromagnetic that opens when the pressure between the hydraulic pump 10 and the attachment cylinder reaches the relief pressure. A relief valve may be provided, and the relief pressure setting unit 24 may set the relief pressure of the electromagnetic relief valve based on the cargo handling load of the cargo handling device 2. At this time, similarly to the above embodiment, the pressure sensor 20 may detect the pressure of the lift cylinder 6 as the cargo handling load of the cargo handling device 2, or the pressure of the attachment cylinder may be detected as the cargo handling load of the cargo handling device 2. Also good.

  The forklift 1 includes an electromagnetic relief valve that opens when the pressure between the hydraulic pump 10 and the lift cylinder 6 reaches the relief pressure. The relief pressure setting unit 24 is configured to perform the electromagnetic relief based on the cargo handling load of the cargo handling device 2. The relief pressure of the valve may be set.

  Furthermore, although the said embodiment is a forklift 1, this invention is applicable if it is an industrial vehicle provided with the cargo handling apparatus.

  DESCRIPTION OF SYMBOLS 1 ... Forklift (industrial vehicle), 2 ... Load handling device, 3 ... Mast, 4 ... Fork, 6 ... Lift cylinder (loading hydraulic cylinder), 7 ... Tilt cylinder (loading hydraulic cylinder), 9 ... Prime mover, 10 ... Hydraulic pressure Pump: 17 ... Proportional relief valve (electromagnetic relief valve), 20 ... Pressure sensor (load detection unit), 24 ... Relief pressure setting unit, 25 ... Relief valve control unit.

Claims (4)

In an industrial vehicle comprising a hydraulic pump driven by a prime mover and a cargo handling device having a plurality of cargo handling hydraulic cylinders operated by hydraulic oil discharged from the hydraulic pump,
An electromagnetic relief valve that opens when the pressure between the hydraulic pump and the hydraulic cylinder for cargo handling reaches a relief pressure;
A load detection unit for detecting a loading load of the loading device;
A relief pressure setting unit that sets the relief pressure based on a cargo handling load of the cargo handling device detected by the load detection unit;
A relief valve control unit that controls the electromagnetic relief valve according to the relief pressure set by the relief pressure setting unit;
The industrial vehicle according to claim 1, wherein the relief pressure setting unit sets the relief pressure higher as a cargo handling load of the cargo handling device is larger. The cargo handling device includes a mast, and a fork attached to the mast for loading a load,
One of the plurality of cargo handling hydraulic cylinders is a lift cylinder for raising and lowering the fork,
The electromagnetic relief valve opens when the pressure between the hydraulic pump and the cargo handling hydraulic cylinder other than the lift cylinder among the plurality of cargo handling hydraulic cylinders reaches the relief pressure,
The load detection unit detects the pressure of the lift cylinder as a cargo handling load of the cargo handling device,
The industrial vehicle according to claim 1, wherein the relief pressure setting unit sets the relief pressure higher as the pressure of the lift cylinder is higher. Another one of the plurality of hydraulic cylinders for cargo handling is a tilt cylinder that tilts the mast forward and backward,
3. The industrial vehicle according to claim 2, wherein the electromagnetic relief valve opens when a pressure between the hydraulic pump and the tilt cylinder reaches the relief pressure.   The relief pressure setting unit sets the relief pressure to a first pressure when a cargo handling load of the cargo handling device is equal to or less than a reference value, and when the cargo handling load of the cargo handling device is larger than the reference value, The industrial vehicle according to any one of claims 1 to 3, wherein the relief pressure is set to a second pressure higher than the first pressure.

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