JP2001010793A - Loading control device for fork lift - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower a fork at a speed intended by an operator by forming a controller so as to output a command current value to be increased with passing of time within the predetermined time from a first current value to a second current value or more to a solenoid proportional valve when operation quantity of a lever exceeds the first current value. SOLUTION: In the case where the operation quantity of a lift lever 22 is increasing more when the lift lever 22 is operated much and a command current value to a solenoid valve 16 exceeds a first current value and in the case where the operation of lever is stopped when the command current value to the solenoid valve 16 exceeds the first current value, the command current value is automatically set by a function of current, and output to the solenoid valve 16. The function of current increases the current from the first current value to the second current value during the rising time independently of the will of an operator. With this structure, even if the operator keeps the operation quantity of the lever corresponding to a pressure difference of a throttle valve at the peak flow value of passing quantity of the throttle valve, the command current value to be output to the solenoid valve 16 is continuously changed from the first current value to the second current value so as to eliminate the pressure difference in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forklift cargo handling control device.

[0002]

2. Description of the Related Art A forklift 40 shown in FIG. 7 drives a pair of left and right front wheels 41, 41 and a pair of left and right rear wheels 42, 41.
It is a four-wheeled vehicle that steers 42. An inner rail 12 is vertically movable between a pair of left and right outer rails 11 erected at the front of a body frame 45 of the forklift 40 so as to be tiltable in the front-rear direction. The finger board 51 is mounted so as to be able to move up and down via a chain (not shown). The piston rod of a lift cylinder 14 disposed on the back surface of the outer rail 11 is connected to the upper end of the inner rail 12. When the operator operates the lift lever 22, the lift cylinder 14 is driven to expand and contract, and the fork 13 moves up and down. It has become. Further, the outer rail 11 is attached to the vehicle body frame 45 by a tilt cylinder 50.
And the operator operates the tilt lever 4
When the user operates the tilt lever 9, the tilt cylinder 50 is driven to expand and contract, and the outer rail 11 is tilted.

[0003] In the forklift 40 described above, when the operator lowers the lift lever 22 greatly when lowering the fork 13 from a height with a load being loaded, a large descent speed unintended by the operator due to gravity. As a result, there is a problem that the speed cannot be controlled well and the working efficiency is impaired. Therefore, fork 1
A down control valve (hereinafter referred to as a throttle valve) is provided in the hydraulic circuit to set the lowering speed of the fork 13 so that the lowering speed of the fork 13 does not become higher than a predetermined speed even when the lift lever 22 is operated in the direction of lowering the fork 13. I have. FIG.
As shown in FIG. 3, this throttle valve 60 is an electromagnetic proportional valve (hereinafter, referred to as an electromagnetic valve 16) for controlling expansion and contraction of the lift cylinder 14.
And the bottom chamber 63 of the lift cylinder 14. When the check valve 61 is arranged in parallel with the throttle valve 60 and the pressure oil is discharged from the solenoid valve 16 to the bottom chamber 63, the check oil flows freely through the check valve 61 and flows into the bottom chamber 6
When returning from 3 to the hydraulic tank 35, the check valve 61
Does not pass through the throttle valve 60. That is, fork 13
When the oil goes down, the oil passes through the throttle valve 60 to control the passing flow rate, thereby controlling the lowering speed of the fork 13. The head chamber 62 of the lift cylinder 14 is directly connected to the hydraulic tank 35 by hydraulic piping.

FIG. 9 shows the characteristics of the throttle valve 60. On the horizontal axis is the throttle valve differential pressure ΔP of the difference between the inlet pressure and the outlet pressure of the throttle valve 60.
s, the vertical axis represents the flow rate Q passing through the throttle valve 60. In the small differential pressure region Zs where the throttle valve differential pressure ΔPs is small,
The passing flow rate Q increases substantially in proportion to the square root of the throttle valve differential pressure ΔPs, and reaches a predetermined set flow rate value Qs. here,
The set flow rate value Qs is a value that determines the lowering speed of the fork 13 under a load. In the middle differential pressure range Zm where the throttle valve differential pressure ΔPs is medium, the passing flow rate Q reaches the peak flow rate value Qp of the maximum passing flow rate value through the set flow rate value Qs, and then gradually decreases to the set flow rate value Qs. Return to The passing flow rate Q in the large differential pressure area Zb where the throttle valve differential pressure ΔPs is the largest holds substantially the set flow rate value Qs. When the fork 13 descends when there is no load, the throttle valve differential pressure ΔPs becomes the maximum when the passing flow rate Q passes through the set flow rate value Qs because the bottom pressure Pb of the bottom chamber 63 of the lift cylinder 14 is smaller than when the fork 13 is loaded. Maintaining the intermediate differential pressure region Zm until the passing flow rate reaches the peak flow rate Qp, the passing flow rate Q can always be increased. Thereby, a large descending speed is obtained when there is no load. Also, when the fork descends with a load, the bottom pressure Pb is larger than when the fork is not loaded. Therefore, the throttle valve differential pressure ΔPs holds the large differential pressure region Zb, and the passing flow rate Q holds the substantially set flow rate value Qs. I do. Thus, when a load is applied, a predetermined lowering speed that is lower than the lowering speed when there is no load is obtained.

[0005]

However, the above technique has the following problems. Fork 13
When the lift lever 22 is operated in the direction of lowering the pressure, the opening area of the return passage of the solenoid valve 16 to the hydraulic tank 35 increases according to the amount of operation, and the differential pressure at the solenoid valve 16 decreases. On the other hand, the differential pressure at the throttle valve 60 increases from a small value to a large value, and reaches a middle differential pressure region Zm having a peak flow rate Qp. In the middle differential pressure range Zm, a peak flow rate Qp larger than the set flow rate Qs flows, and a fork lowering speed higher than the speed desired by the operator is generated. Thereafter, when the operation amount of the lift lever 22 is further increased, the throttle valve differential pressure ΔPs reaches the large differential pressure region Zb,
The passing flow rate Q keeps the set flow rate value Qs, and the desired lower speed of the fork is obtained. As described above, in the process of shifting from the small differential pressure area Zs to the large differential pressure area Zb, the operator has a passage opening area of the solenoid valve 16 that becomes a differential pressure in the medium differential pressure area Zm that generates the peak flow rate value Qp. The lever operation amount can be held. That is, it is necessary to pass through the middle differential pressure region Zm where the peak flow value Qp occurs before reaching the large differential pressure region Zb where the set flow value Qs occurs, and the state of the middle differential pressure region Zm can be maintained. .
As a result, when the fork 13 is loaded, the fork 13 may descend at a large speed not intended by the operator, and it becomes difficult to accurately position the fork 13.
There is a problem that the speed controllability at the time of cargo handling is not good.

The present invention has been made in view of the above problems, and has as its object to provide a cargo handling control device for a forklift in which a fork descends at a speed intended by an operator under a load.

[0007]

In order to achieve the above object, a first aspect of the present invention provides an electromagnetic proportional valve for controlling expansion and contraction of a lift cylinder for raising and lowering a fork, and a lever for detecting a lever operation amount. With the manipulated variable detector, when the differential pressure is small, the passing flow rate is increased in accordance with the differential pressure, and after passing through the first differential pressure that produces a predetermined set flow rate value, the set flow rate value is set when the differential pressure is larger than the first differential pressure After taking a larger peak flow value, decrease the flow rate as the differential pressure increases,
When the differential pressure is equal to or higher than a predetermined second differential pressure, a down control valve for controlling a fork lowering speed whose passing flow rate is set based on the differential pressure so as to maintain the set flow rate value, And a controller for calculating a command current value and outputting the command current value to the electromagnetic proportional valve, the controller comprising: a predetermined first current value to the electromagnetic proportional valve corresponding to the first differential pressure of the down control valve; And a predetermined second current value to the electromagnetic proportional valve corresponding to the second differential pressure is stored, and when the lever operation amount is larger than the first current value, a current value greater than or equal to the second current value from the first current value A command current value that increases as time elapses within a predetermined time period is output to the electromagnetic proportional valve.

According to the first invention, the down control valve used in the hydraulic circuit to which the present invention is applied takes a large flow rate to increase the descending speed when no load is applied with a small differential pressure. When the load is large, reduce the flow rate to reduce the descent speed,
The passing flow rate is set according to the differential pressure. When the lever operation amount is increased in the direction for lowering the fork from zero, the opening area of the electromagnetic proportional valve increases, and the differential pressure of the down control valve becomes the first differential pressure that passes the set flow rate value. The first current value of the solenoid valve corresponding to the first differential pressure is stored in the controller. Further, the controller also stores the second current value of the solenoid valve corresponding to the differential pressure that causes the set flow rate value to pass again after passing through the differential pressure range where the peak flow rate value occurs. The operator increases the lever operation amount, and increases or decreases when the command current value to the solenoid proportional valve is larger than the first current value and is still increasing, or when the command current value is larger than the first current value. If not, the command current value to the solenoid proportional valve is increased from the first current value to a current value equal to or more than the second current value within a predetermined time. Thereby, even if the operator holds the lever operation amount in the differential pressure region of the large flow rate of the down control valve, the command current value to the electromagnetic proportional valve changes the differential pressure region of the large flow volume in a predetermined short time. When the time is substantially zero, the forklift passes in a step-like manner and does not maintain a large flow rate, so that a forklift loading / unloading control device can be obtained in which the fork descends at a speed intended by the operator under load.

In a second aspect based on the first aspect, a pressure detector (64) for detecting a bottom pressure of the lift cylinder is additionally provided,
The controller determines that the fork is carrying a load based on the detected bottom pressure, and when the lever operation amount is larger than the first current value, the controller determines a predetermined value from the first current value to a current value equal to or more than the second current value. The command current value that increases as time elapses within the time period is output to the electromagnetic proportional valve.

According to the second invention, when the bottom pressure is larger than the predetermined pressure threshold value, it is determined that the load is applied, and the command current value is changed from the first current value to a current value equal to or more than the second current value within a predetermined time. To increase over time. This allows
Even if the operator holds the lever operation amount in the differential pressure range of the large flow rate of the down control valve, the command current value to the solenoid proportional valve is substantially zero time in the differential pressure range of the large flow rate in a predetermined short time. In this case, the fork descends at a speed intended by the operator because the fork passes through in a stepwise manner and does not maintain a large flow rate.
Further, when the bottom pressure is equal to or lower than the predetermined pressure threshold, that is, when there is no load, the operator can finely set the command current value to the electromagnetic proportional valve by the lever operation amount. With these, depending on the speed intended by the operator when there is a load,
Further, it is possible to obtain a forklift loading / unloading control device that controls the fork lowering speed at a fine speed set by lever operation when no load is applied.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a hardware configuration. The same components as those in FIGS. 7 and 8 are described with the same reference numerals. The chain 19 hanging from the upper end of the finger board 51 is connected to a pulley 15 provided on the rod of the lift cylinder 14.
And is fixed to the upper part of the outer rail 11 through the center. The lift cylinder 14 is provided between the bottom chamber 63 of the lift cylinder 14 and the hydraulic pump 20 driven by the electric motor 21.
The solenoid valve 16 for controlling the expansion and contraction of the throttle valve and the throttle valve 60 and the check valve 61 are connected by a pipe via a circuit connected in parallel. The solenoid valve 16 has an ascending port 65, a neutral port 66, and a descending port 67.
When lowering 3, the lowering port operates. The head chamber 62 of the lift cylinder 14
Is directly connected to the hydraulic tank 35 via a hydraulic pipe.
Further, a lift lever 22 for outputting a command to the electromagnetic valve 16 is provided on an operator's seat (not shown).

A pressure detector 64 for detecting the bottom pressure Pb of the bottom chamber 63 of the lift cylinder 14 is attached to the bottom chamber 63 as a detector. Also, lift lever 2
A lever operation amount detector 24 for detecting the lever operation amount Le is provided in the vicinity of the center of rotation of 2.

A controller 26 for calculating a control command to be output to the solenoid valve 16 and the electric motor 21 has a bottom pressure Pb detected by the pressure detector 64 and a lever operation amount Le from the lever operation amount detector 24. Input circuit (not shown)
Has been entered through. Further, the controller 26
A command current value Iv for commanding the valve opening degree to the solenoid valve 16 and an energization on / off command Sm for commanding the electric motor 21 to rotate or stop are output via a drive circuit (not shown).

Here, the relationship among the passing flow rate Q, the bottom pressure Pb, the throttle valve differential pressure ΔPs, and the solenoid valve differential pressure ΔPv when the fork 13 is lowered at the rated load will be described with reference to FIGS. The value obtained by dividing the weight of the rated load by the bottom area of the lift cylinder 14 is the bottom pressure Pb. When the fork 13 is descending, the bottom pressure Pb is substantially maintained. At this time, as shown in FIG.
And the solenoid valve 16 are arranged in series, so that the throttle valve differential pressure ΔPs and the solenoid valve differential pressure ΔPv have the relationship of equation (1). Pb = ΔPs + ΔPv (1) On the other hand, as shown in FIG. 3, the throttle valve differential pressure ΔPs when the throttle valve differential pressure ΔPs increases and the passing flow rate Q reaches the set flow rate value Qs. Is the throttle valve first differential pressure ΔPs1, and the electromagnetic valve differential pressure ΔPv at this time is the electromagnetic valve first differential pressure ΔPv1. The electromagnetic valve first differential pressure ΔPv1 is expressed by Expression (2). The bottom pressure Pb and the throttle valve first differential pressure ΔPs1 are known. ΔPv1 = Pb−ΔPs1 (2) As shown in FIG. 4, the differential pressure-flow rate characteristic of the solenoid valve is such that the passing flow rate Q depends on the command current value Iv commanded to the solenoid valve 16. Flow rate. Since the set flow rate Qs of the passing flow rate Q and the solenoid valve first differential pressure ΔPv1 as the solenoid valve differential pressure ΔPv are known values, FIG. 4 shows that the passing flow rate Q is the set flow rate Qs, When the solenoid valve differential pressure ΔPv
The first current value Iv1 of the solenoid valve 16 that satisfies the condition of the pressure difference ΔPv1 is obtained. At the obtained first current value Iv1, the throttle valve differential pressure ΔPs takes the value of the throttle valve first differential pressure ΔPs1. When the command current value Iv to the solenoid valve 16 is increased to increase the opening area, the throttle valve differential pressure ΔPs becomes larger, and the flow rate Q passing through the throttle valve reaches the peak flow rate Qp as shown in FIG. Later, it approaches the set flow rate value Qs again. The throttle valve differential pressure ΔPs when the flow rate approaches the set flow rate value Qs again is defined as the throttle valve second differential pressure ΔPs2. At this time, the corresponding solenoid valve differential pressure ΔPv is set to the solenoid valve second differential pressure ΔPv2, and the command current value Iv of the solenoid valve 16 is set to the second current value Iv2.

FIG. 5 shows that the command current value I to the solenoid valve 16 when the fork 13 is lowered at the rated load.
The temporal change of v will be described. In FIG. 5, the horizontal axis represents time t, and the vertical axis represents the command current value Iv. When the time t is zero, the command current value Iv is set to a zero value. As the operator increases the operation amount of the lift lever 22 in the direction in which the fork descends, the command current value Iv reaches the first current value Iv1. Subsequent command current value Iv
Is set from the first current value Iv1 to the second current value Iv2 by a current function f (t) that increases with time within a predetermined rise time ΔT seconds. The command current value Iv does not take a value larger than the second current value Iv2. When the operator reverses and decreases the lever operation amount Le after the command current value Iv becomes larger than the first current value Iv1, the command current value Iv passes through the first path P1 or the second path P2. . That is, when the command current value Iv is larger than the first current value Iv1, and when the lever operation amount Le is reversed from an increase to a decrease, the command current value Iv assumes the first current value Iv1.

Next, the processing operation of the controller will be described with reference to the flowchart of FIG. The processing steps in FIG. 6 are denoted by adding S. In S1, it is determined whether or not the lever operation amount Le is a value in a direction in which the fork 13 is lowered. If the value is in the direction of raising the fork 13, the command current value Iv corresponding to the lever operation amount Le is calculated in S7 and output to the solenoid valve 16. If the value is in the direction of lowering the fork 13, it is determined in S2 whether the bottom pressure Pb is larger than the bottom threshold pressure Pbs. Here, the bottom threshold pressure Pb
s is a pressure smaller than the bottom pressure Pb when the fork 13 is carrying the rated load by a predetermined pressure. When the pressure is equal to or lower than the bottom threshold pressure Pbs, the lever operation amount Le is determined in S7.
And outputs it to the solenoid valve 16. When it is larger than the bottom threshold pressure Pbs, it is determined whether the command current value Iv is larger than the first current value Iv1. When the current value is equal to or less than the first current value Iv1, the command current value Iv corresponding to the lever operation amount Le is calculated in S7, and the solenoid valve 1 is operated.
6 is output. When it is larger than the first current value Iv1, it is determined in S4 whether or not the lever operation differential value Led, which is the temporal change rate of the lever operation amount Le, is equal to or greater than a zero value. If the lever operation differential value Led is smaller than the zero value, the command current value Iv is set to the first current value Iv1 and output to the solenoid valve 16 in S6. If the lever operation differential value Led is equal to or greater than zero, it is determined in S5 whether or not the state in which the command current value Iv is greater than the first current value Iv1 has continued for the startup time ΔT seconds. If the start-up time ΔT has not been maintained, the current value Iv is set by the function f (t) and output to the solenoid valve 16 in S8. Start-up time ΔT
If so, the current value Iv is set to the second current value Iv2 and output to the solenoid valve 16 in S9.

Next, the operation of the present embodiment will be described. When lowering the fork 13 at the rated load, when the operator operates the lift lever 22 in the lowering direction of the fork 13, the lever operation amount Le detected by the lever operation amount detector 24 is input to the controller 26, and the controller 26 receives the input. A command current value Iv corresponding to the operated lever operation amount Le is output to the solenoid valve 16. At this time, the opening area of the solenoid valve 16 on the circuit leading from the bottom chamber 63 of the lift cylinder 14 to the hydraulic tank 35 gradually increases, and the flow rate Q passing through this opening area gradually increases, and the solenoid valve 16 The differential pressure at 16 becomes smaller. On the other hand, the throttle valve 6
Since the flow rate Q of 0 is the same, the differential pressure of the throttle valve 60, which was small when the opening area of the solenoid valve 16 started to open, increases according to the opening area of the solenoid valve 16. Then, when the command current value Iv is the opening area of the solenoid valve 16 when the first current value Iv1 is reached, the throttle valve differential pressure ΔPs reaches the first throttle valve differential pressure ΔPs1.

Further, the case where the command current value Iv to the solenoid valve 16 becomes larger than the first current value Iv1 by operating the lift lever 22 greatly and the lever operation amount Le further increases, When the movement of Le stops there, the command current value Iv is automatically set by the current function f (t) shown in FIG. The current function f (t) is calculated from the first current value Iv1 to the second current value Iv2.
Up to ΔT seconds regardless of the operator's intention. Thereby, even if the operator holds the lever operation amount Le corresponding to the differential pressure of the throttle valve when the passing flow rate Q of the throttle valve takes the peak flow value Qp, the command current value Iv output to the solenoid valve 16 is Since the first current value continues to change from the second current value, the differential pressure that causes the peak flow value Qp is not held for a long time.

As a result, the operator operates the lever operation amount L
Even when e is held in the middle differential pressure region Zm where the peak flow value Qp occurs, the command current value Iv to the solenoid valve 16 passes through the middle differential pressure region Zm in a very short time, and holds the peak flow value Qp. Therefore, it is possible to obtain a forklift cargo handling control device in which the fork descends at a speed intended by the operator when a load is applied.

The predetermined start-up time Δ in FIG.
When T seconds are shortened and set to almost zero value, the peak flow rate Q
Since the time required to pass through the medium differential pressure region Zm where p occurs becomes substantially zero, it is possible to obtain a fork descent speed which is not affected by the peak flow rate Qp. At this time, the medium differential pressure region Z
m in a short time, due to the characteristics of the throttle valve 60,
Since the peak flow value Qp may appear in the form of a momentary hydraulic shock, the startup time ΔT seconds is equal to the peak flow value Qp.
Is set so as to reduce the influence on the descending speed and to reduce the hydraulic shock.

In this embodiment, the first differential pressure ΔPs1
From the first current value Iv1 corresponding to the second differential pressure ΔPs2 to the second current value Iv2 corresponding to the second differential pressure ΔPs2 as the current function f (t) which starts in the startup time ΔT seconds, the second differential pressure ΔP
The second current value Iv2 corresponding to s2 may be set to the maximum current value that can be output to the solenoid valve. Further, in FIG. 5, the temporal change from the first current value Iv1 to the second current value Iv2 is indicated by a straight line, but the first current value Iv1
To a second current value Iv2 as long as the time elapses.

Further, in the present embodiment, when the detected bottom pressure Pb is larger than a predetermined bottom threshold pressure Pbs, the command current value Iv is changed from the first current value Iv1 to the second current value Iv2.
It will increase as time goes by. When there is no load when the magnitude of the bottom pressure Pb is determined, as shown in S7 of FIG.
Takes a value corresponding to the lever operation amount Le. This allows
The operator can finely set the command current value Iv that keeps the vicinity of the differential pressure that causes the peak flow value Qp by the lever operation amount Le. Here, since the bottom pressure Pb when the fork 13 is not loaded is smaller than when the fork 13 is loaded, if the throttle valve differential pressure ΔPs when the fork 13 is lowered is large up to the second differential pressure ΔPs2 shown in FIG. However, depending on the characteristics of the throttle valve, the first differential pressure ΔPs1 and the second differential pressure ΔPs
It may take an intermediate value of 2. In this case, even if the second command current Iv2 corresponding to the second differential pressure ΔPs2 is output as the command current value Iv, the throttle valve differential pressure ΔPs is equal to the first current.
A value between the differential pressure ΔPs1 and the second differential pressure ΔPs2 is held. Thereby, even when the command current value Iv is increased from the first current value Iv1 to the second current value Iv2 with time when no load is applied, the passing flow rate Q of the throttle valve 60 is constant at a value close to the peak flow rate value Qp. Holds the value. That is, regardless of the size of the load, even if the command current value Iv to the solenoid valve is always automatically increased from the first current value Iv1 to the second current value Iv2 with the passage of time, the load is determined. It has the same effect as. Further, when there is no load judgment, the pressure detector 64 is not required, so that an inexpensive control device can be obtained.

As described above, according to the present invention, when the target hydraulic circuit lowers the fork, the oil discharged from the bottom chamber of the lift cylinder returns to the hydraulic tank via the throttle valve and the solenoid valve. At this time, when there is no load with a small differential pressure, the passing flow rate passing through the throttle valve is increased to increase the descending speed, and when the load is large, the passing flow rate is decreased to decrease the descending speed. ,
The opening area of the throttle valve is set according to the differential pressure. When the lever operation amount is increased in the direction of lowering the fork from zero, the opening area of the solenoid valve increases, and the differential pressure of the throttle valve becomes a differential pressure that produces a set flow rate value before becoming a differential pressure that produces a peak flow rate value. The first of the solenoid valves corresponding to the differential pressure at this time
The current value is stored in the controller. Further, the controller also stores the second current value of the solenoid valve corresponding to the differential pressure at the time when the differential pressure region where the set flow value is generated again after passing through the differential pressure region where the peak flow value is generated. The operator
When the lever operation amount is increased and the command current value to the solenoid valve is larger than the first current value and is still increasing, or when the command current is larger than the first current value and there is no increase / decrease change, The command current value to the solenoid valve is increased from the first current value to a current value equal to or more than the second current value in a predetermined rise time. Thereby, even if the operator holds the lever operation amount in the large differential pressure area of the passing flow rate, the command current value to the solenoid valve passes through the differential pressure area of the large passing flow rate in an extremely short time, and the large passing flow rate is reduced. Since it is not held, it is possible to obtain a forklift loading / unloading control device in which the fork descends at a speed intended by the operator when a load is applied.

[Brief description of the drawings]

FIG. 1 is a hardware configuration diagram according to the present invention.

FIG. 2 is an explanatory diagram of a relationship among a bottom pressure, a throttle valve differential pressure, a solenoid valve differential pressure, and a flow rate when a fork is lowered.

FIG. 3 is an explanatory diagram of a throttle valve first differential pressure, a throttle valve second differential pressure, a set flow rate value, and a peak flow rate value.

FIG. 4 is an explanatory diagram of a differential pressure-flow rate characteristic of a solenoid valve.

FIG. 5 is an explanatory diagram of a temporal change of a command current value to a solenoid valve in the present embodiment.

FIG. 6 is a flowchart of a controller.

FIG. 7 is an explanatory diagram of a forklift to which the present invention is applied.

FIG. 8 is a schematic diagram of a hydraulic circuit when a fork is lowered.

FIG. 9 is an explanatory diagram of a differential pressure-flow rate characteristic of a throttle valve.

[Explanation of symbols]

11: outer rail, 12: inner rail, 13: fork, 14: lift cylinder, 16: solenoid proportional valve, 20
... hydraulic pump, 21 ... electric motor, 22 ... lift lever, 24 ... lever operation amount detector, 26 ... controller,
60: down control valve, 61: check valve,
64: pressure detector, Sm: energization on / off signal, Le: lever operation amount, Led: lever operation differential value, Iv: command current value, Iv1: first current value, Iv2: second current value, ΔP
1: first differential pressure, ΔP2: second differential pressure, ΔPs: throttle valve differential pressure, ΔPv: solenoid valve differential pressure, Q: passing flow rate, Qp: peak flow value, Qs: set flow value, Pb: bottom pressure, Pbs ...
Bottom threshold pressure, ΔT: rise time, f (t): current function,
Zs: small differential pressure area; Zm: medium differential pressure area; Zb: large differential pressure area.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Ikuo Hayama 110 Yokokura Nitta, Oyama City, Tochigi Prefecture Komatsu Forklift Co., Ltd. Tochigi Plant F-term (reference) 3F333 AA02 AB13 BA02 BD02 FA21 FA29 FB04 FD06 FD08 FE04 FE09

Claims (2)

[Claims] An electromagnetic proportional valve for controlling expansion and contraction of a lift cylinder for raising and lowering a fork, a lever operation amount detector for detecting a lever operation amount, and when a differential pressure is small, a passing flow rate is increased according to the differential pressure; After passing through a first differential pressure that produces a predetermined set flow value, and taking a peak flow value that is larger than the set flow value when the differential pressure is larger than the first differential pressure, the passing flow rate is decreased as the differential pressure increases. When the differential pressure is equal to or higher than a predetermined second differential pressure, a down control valve for controlling the fork lowering speed, the passing flow rate of which is set based on the differential pressure, so as to maintain the set flow rate value; In the forklift loading / unloading control device including a controller that calculates a command current value in response to the command value and outputs the command current value to the electromagnetic proportional valve, the controller corresponds to the first differential pressure of the down control valve. A predetermined first current value to the electromagnetic proportional valve and a predetermined second current value to the electromagnetic proportional valve corresponding to the second differential pressure are stored, and when the lever operation amount is larger than the first current value, the first current value is stored. A load control device for a forklift, wherein a command current value that increases as time elapses from a current value to a current value equal to or more than a second current value within a predetermined time is output to an electromagnetic proportional valve. 2. The cargo handling control device for a forklift according to claim 1, further comprising a pressure detector (64) for detecting a bottom pressure of the lift cylinder, wherein the controller loads the fork with a load based on the detected bottom pressure. And when the lever operation amount is larger than the first current value, the command current value that increases from the first current value to a current value that is equal to or greater than the second current value within a predetermined time as time elapses is determined. A cargo handling control device for a forklift, which outputs the output to an electromagnetic proportional valve.