JP2706382B2 - Forklift control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control apparatus for a forklift, and more particularly to a control apparatus useful for a forklift having an unload valve for unloading a pilot pressure when a hydraulic cylinder is not loaded.

[0002]

2. Description of the Related Art A forklift is an industrial vehicle for cargo handling in which a mast for raising and lowering loaded luggage is provided in front of a vehicle body so as to be able to move between locations.

The above-mentioned forklift replaces a conventional mechanical forklift, that is, transmits the operation amount of an operation lever to a control valve via a mechanical link mechanism, and controls the opening of the control valve to reduce the amount of oil. Instead of the one that adjusts the speed of elevating and lowering by controlling, the electronic control type that can perform predetermined control by operating the work equipment lever with a remarkably light operating force is rapidly increasing It is widespread.

FIG. 6 is a block diagram showing a control device of an electronically controlled forklift according to the prior art together with a hydraulic system. As shown in FIG.
b denotes hydraulic cylinders 02a, 02 for raising and lowering and tilting.
The operation of b is for controlling each operation, and a lever operation signal, which is an electric signal corresponding to the operation amount, is transmitted to the controller 03. Controller 0
3 processes each lever operation signal and processes the electromagnetic proportional control valve 04
A flow control signal, which is an electric signal for controlling the opening degree of a and 04b, is sent out. That is, each flow rate control signal is controlled by the solenoid proportional control valves 04a and 04b by controlling the amount of movement of the spool in accordance with the respective current value via the pilot pressure.
The opening degree is controlled.

The above-mentioned flow control signal is transmitted to the work implement lever 01
The operation amounts a and 01b have characteristics as shown in FIG. That is, there is a dead zone in the vicinity of the neutral position of the working machine levers 01a and 01b, and a portion beyond this dead zone transmits a flow control signal having a value corresponding to the operation amount of the working machine levers 01a and 01b. It has become.

The back pressure valve 05 holds the pressure oil so that the minimum hydraulic pressure on the upstream side is equal to or higher than the pilot pressure of each of the electromagnetic proportional control valves 04a and 04b. Thus,
The pilot pressure of the pilot hydraulic system is generated by pressure oil diverted upstream of the back pressure valve 05, and constitutes an internal pilot type hydraulic system.

[0007] The unload valve 06 is provided with an operation lever 01a,
Only when the position of 01b is in the work area, the bypass line 07 is closed to generate pilot pressure, and the bypass line 07 is normally opened so that the pressure oil bypasses the back pressure valve 05.

The reason for providing the unload valve 06 is as follows. That is, in the method in which the minimum hydraulic pressure of the hydraulic circuit is maintained at the pilot pressure or higher by the back pressure valve 05, the pressure is constantly maintained for the entire flow rate, so that the energy loss is large. This is because when the position is in the dead zone, the energy loss is reduced by making the pressure oil bypass the back pressure valve 05.

In the forklift control device having the unload valve 06 in the hydraulic system as described above, the unload valve 06 operates at a position slightly closer to the neutral point than the boundary between the dead zone and the work area shown in FIG. After closing the bypass line 07 and establishing pilot pressure, the work area is entered,
The controller 3 controls the electromagnetic proportional control valves 04a and 04b to start the control. In other words, the operating positions of the unload valve 06 and the electromagnetic proportional control valves 04a and 04b are shifted so that the operation of the electromagnetic proportional control valves 04a and 04b is performed after the pilot pressure is stabilized.

[0010]

As described above, in the prior art in which the operation timings of the unload valve 06 and the electromagnetic proportional control valves 04a, 04b are shifted, the operating speed of the work implement levers 01a, 01b is high. In this case, before the pilot pressure is stabilized, the electromagnetic proportional control valves 04a, 04
b operates, and in this case, there is a problem that the hunting phenomenon H of the pilot pressure occurs as shown in FIG. 8 and the operation of the hydraulic system becomes unstable.

The present invention has been made in view of the above-mentioned prior art, and has as its object to provide a control device for a forklift capable of stabilizing the operation of an internal pilot type hydraulic system having an unload valve for reducing power loss. .

[0012]

The structure of the present invention to achieve the above object is as follows.

An internal pilot type electromagnetic proportional control valve for controlling a flow rate of hydraulic oil flowing through a hydraulic line for supplying hydraulic oil to a hydraulic cylinder as a working machine by moving a spool by a pilot pressure; A forklift control device including a hydraulic system having an unload valve for unloading a work machine, a work machine lever for transmitting a lever operation signal that is an electric signal corresponding to an operation amount, and It detects that the machine lever has entered the work area beyond the dead zone near the neutral position, activates the unload valve at the same time as this detection, turns the pilot pressure on-load, and after a predetermined time elapses, A controller that sends out a flow control signal that controls the opening of the electromagnetic proportional control valve so that the flow rate of pressure oil in the pipeline becomes a flow rate that corresponds to the lever operation signal. Characterized in that it has and.

[0014]

According to the present invention having the above construction, when the position of the working machine lever enters the working area by operating the working machine lever, first, the unloading valve is operated to raise the pilot pressure, and after a predetermined time elapses, the electromagnetic pressure is increased. The proportional control valve starts to operate.
That is, a predetermined time until the pilot pressure after the operation of the unload valve stabilizes can be always secured regardless of the operation speed of the work implement lever.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 4 is a perspective view showing an example of a forklift to which the present embodiment is applied. As shown in the figure, the lift cylinder 1 is fixed to a pair of left and right outer masts 2, and lifts and lowers a pair of left and right inner masts 3 using the outer mast 2 as a guide as the piston rod 1a expands and contracts. . At this time, the outer mast 2 is fixed to the vehicle body 6 in front of the vehicle body 6. As a result, as the inner mast 3 is moved up and down, the elevating unit composed of the bracket 5 suspended on the chain (not shown) and the fork 4 for directly loading luggage is moved up and down.

The tilt cylinder 7 moves up and down together with the outer mast 2 and the inner mast 3 in front of the vehicle (without the vehicle body 6).
Side) and rearward (toward the vehicle body 6). That is, in the case of unloading, it tilts forward, and in the case of unloading and transporting luggage, it tilts rearward, so that the respective workability is maintained well and safety is ensured.

The working machine levers 8a and 8b are used to control the operation of the lift cylinder 1 and the tilt cylinder 7 via the controller 9 and the electromagnetic proportional control valve 10 by the operator operating them, and perform an emergency stop. Together with the safety switch 11 for joystick. Work implement levers 8c, 8d, 8e
Is for dealing with the case where various attachments, for example, a roll clamp, a bale clamp, etc. are attached. The seat switch 13 is a switch that operates when the operator sits on the driver's seat 14, and outputs an output signal to the controller 9.

FIG. 5 is a block diagram showing an example of the forklift control device. In the figure, the same parts as those of FIG. 4 are denoted by the same reference numerals, and duplicate description is omitted.

As shown in FIG. 5, the working machine levers 8a and 8
“b” is formed by a potentiometer and sends a lever operation signal S ₁ whose current value is proportional to the operation amount to the controller 9. The controller 9 sends a flow control signal S ₂ to adjust the degree of opening of the spool of the electromagnetic proportional control valve 10 on the basis of the lever operation signal S _1. By electromagnetic proportional control valve 10 to its spool in proportion to the magnitude of the flow control signal S ₂ travels via the pilot pressure of the hydraulic system of the internal pilot type, controls the flow rate of the hydraulic fluid flowing through the hydraulic line 15 Then, the operation speeds of the lift cylinder 1 and the tilt cylinder 7 are controlled so as to correspond to the operation amounts of the working machine levers 8a and 8b.

The hydraulic pressure sensor 16 is disposed in the hydraulic line 15 and sends out a hydraulic signal S ₃ indicating the pressure of the hydraulic oil in the hydraulic line 15. Unload valve 17 is bypass line 18
When the lift cylinder 1 and the tilt cylinder 7 are stopped, the bypass line 18 is opened, and the pressure oil pumped up by the hydraulic pump 19 is returned to the hydraulic oil source 20.

The controller 9 hydraulic signal while calculating the load load acting on the lift cylinders 1 and tilt cylinders 7 processes the S _3, the opening and closing operation signal S ₄ of the unloading valve 17 processes the lever operation signals S ₁ Is sent.

Further, the controller 9 is operated by being supplied with electric power from the battery 24 by turning on a starter switch 23 housed in the console box 22 together with the warning light 21, and when the safety switch 11 is operated and when the seat switch 13 is operated. electromagnetic proportional control valve as zero current value of the flow rate control signal S ₂ when not in operation 10
Is controlled so that the opening degree of is zero.

In the figure, reference numeral 19 denotes a hydraulic pump, and reference numeral 20 denotes a hydraulic oil source. Also, the electromagnetic proportional control valve 10, the hydraulic line 1
5. Hydraulic components such as the oil pressure sensor 16
The number corresponding to the number of a to 8e is provided. In the present embodiment, since two working machine levers 8a and 8b for lifting and lowering and tilting are provided to perform lifting and lowering and tilting operations, two hydraulic systems are provided.

FIG. 1 is a block diagram showing a control device in which main parts of the present embodiment are extracted. In the figure, the same parts as those in FIGS. 4 and 5 are denoted by the same reference numerals, and redundant description will be omitted.

As shown in FIG. 1, the working machine levers 8a, 8
b sends the lever operation signal S ₁ to the control amount extracting means 25.
And the lever position detection sensor 26. Controlling extraction means 25 sends the flow control signal S ₂ representing a control amount corresponding to the lever operation signals S ₁ refers to the operation amount / controlled variable correspondence table 27. That is, the operation amount / control amount correspondence table 27 has a flow rate control signal S ₂ having characteristics as shown in FIG. 7 corresponding to the operation amounts of the work implement levers 8a and 8b.
Are stored in a one-to-one correspondence.

The lever position detecting sensor 26, based on the lever operation signal S _1, work machine levers 8a, when the position of 8b detects that it has entered the work area (see FIG. 7), the opening and closing operation to the unload valve 17 supplying a signal S _4, together make a pilot pressure by closing the unload valve 17, the timer 28 supplies a measurement start signal S ₅ so as to start measuring operation of the timer 28. On the other hand, after detecting that a dead zone has been entered from the work area, the control amount output means 2
9 sends a reset signal S _7. Timer 28 when the measured value of the time was started by the measurement start signal S ₅ has reached a predetermined value, i.e., when a predetermined time set in advance has elapsed, supplies the set signal S ₆ to the control amount output unit 29.
At this time, the predetermined time of the timer 28 is a time required for the pilot pressure to rise and to be in a state sufficient for stabilization. The control amount output means 29 sends the flow rate control signal S ₂ sent from the control amount extraction means 25 to the electromagnetic proportional control valve 10 on condition that the set signal S ₆ is input.

According to the above embodiment, the working machine levers 8a,
When the position of the working machine levers 8a and 8b enters the working area from the dead zone by the operation of 8b, first, the unload valve 17 is operated to close the bypass pipeline 18. As a result, pilot pressure builds up.

After the operation of the unload valve 17, until the predetermined time elapses, the state in which the unload valve 17 is operating but the electromagnetic proportional control valve 10 is not operating continues for a predetermined time. During this time, the pilot pressure stabilizes.

After a predetermined time has elapsed, the flow rate control signal S ₂ is supplied to the electromagnetic proportional control valve 10 via the control amount output means 29 to control the amount of pressure oil supplied to the lift cylinder 1 and the tilt cylinder 7. Is done. As a result, as shown in FIG. 2, the pilot pressure rises satisfactorily and is maintained at a predetermined value.

The work machine lever 8a, a bypass pipe pressure oil pumped from the hydraulic fluid source 20 by opening the unloading valve 17 by opening and closing the signal S ₄ when the 8b is entered the dead band and from the work area when located in the dead zone It is returned to the hydraulic oil source 20 via the path 18.

FIG. 3 shows a flow chart of the above series of operations.

[0033]

According to the present invention, as described above in detail with the embodiment, the electromagnetic proportional control valve operates after the pilot pressure stabilizes regardless of the operating speed of the work implement lever. Thus, stable control can be realized without causing a hunting phenomenon at the time of rising.

[Brief description of the drawings]

FIG. 1 is a block diagram extracting and showing main parts of a control device according to an embodiment of the present invention.

FIG. 2 is a graph showing a rise characteristic of a pilot pressure in the embodiment.

FIG. 3 is a flowchart showing the operation of the embodiment.

FIG. 4 is a perspective view showing a forklift to which the embodiment of the present invention is applied.

FIG. 5 is a block diagram showing the entire control device according to the embodiment of the present invention.

FIG. 6 is a block diagram showing a control device of an electronically controlled forklift according to the related art together with a hydraulic system.

FIG. 7 is a characteristic diagram illustrating a relationship between an operation amount of a work implement lever and a level of a flow control signal.

FIG. 8 is a graph showing a rising characteristic of pilot pressure in the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Lift cylinder 7 Tilt cylinder 9 Controller 10 Electromagnetic proportional control valve 15 Hydraulic line 17 Unload valve Dead zone Work area S ₁ Lever operation signal S ₂ Flow control signal

 ──────────────────────────────────────────────────続 き Continued from the front page (72) Inventor Toshiyuki Midorikawa 3000 Tana, Sagamihara-shi, Kanagawa M.H.

Claims (1)

(57) [Claims] 1. An internal pilot type electromagnetic proportional control valve for controlling a flow rate of hydraulic oil flowing through a hydraulic pipeline for supplying hydraulic oil to a hydraulic cylinder as a working machine by moving a spool by a pilot pressure; In a control device for a forklift equipped with a hydraulic system having an unload valve for setting a pilot pressure to an unload state, a work implement lever for transmitting a lever operation signal that is an electric signal corresponding to an operation amount, and a lever based on the lever operation signal Detects that the work equipment lever has entered the work area beyond the dead zone near the neutral position, activates the unload valve at the same time as this detection to turn the pilot pressure on-load, and after a predetermined time has elapsed. , A controller that sends a flow control signal to control the opening of the electromagnetic proportional control valve so that the flow rate of the hydraulic oil in the hydraulic pipeline becomes a flow rate corresponding to the lever operation signal And a control device for a forklift.