JPH11209092A - Fork shift device for forklift - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the view area of an operator by preventing the useless motion of a fork except in shift operation and simplifying a piping system as well. SOLUTION: Pilot operated check valves 7A, 7B, 24A, 24B are installed in hydraulic pipe passages 4A, 4B, 5A, 5B on sides of fork opening/closing operation provided for hydraulic cylinders 20A, 20B for a forklift. The hydraulic cylinders 20A, 20B are hydraulically locked with the pilot operated check valves 7A, 7B, 24A, 24B except in shift operation to prohibit the movement of forks 3A, 3B with external force. Two check valves 7A, 24A and 7B, 24B are unitized into valve units 27A, 27B not to possibly shut the front view of an operator with a piping system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shift fork device as one of attachments of a forklift (forklift truck), and more particularly to a hydraulic piping system attached to a hydraulic cylinder for adjusting a distance between a pair of forks. Regarding improvement.

[0002]

2. Description of the Related Art A shift fork device of a forklift includes a pair of forks slidably mounted on a carriage (finger bar) and hydraulic cylinders individually provided for each fork. Basically, the distance between the forks can be adjusted arbitrarily by operating the forks close to and away from each other, but the structure shown in FIGS. 4 and 5 is adopted as a specific configuration of the hydraulic circuit. ing.

As shown in FIG. 1, each hydraulic cylinder 1A,
1B is a corresponding fork 3
A or 3B, each hydraulic cylinder 1A,
The interval between the forks 3A, 3B is widened by the extension operation of 1B, and conversely, the interval between the forks 3A, 3B is narrowed by the contraction operation of each hydraulic cylinder 1A, 1B.

When the hydraulic cylinders 1A, 1B of the hydraulic pipelines attached to the hydraulic cylinders 1A, 1B are extended (when the gap between the forks 3A, 3B is opened), the hydraulic cylinders 1A, 1B are supplied with hydraulic pressure. Are introduced into the fork opening operation side hydraulic lines 4A and 4B, and when the hydraulic cylinders 1A and 1B are contracted (forks 3A and 3B).
At the time of the closing operation of the interval between each other), each hydraulic cylinder 1A, 1B
Assuming that the hydraulic lines for introducing hydraulic pressure to the fork closing operation side hydraulic lines 5A and 5B are the pilot operation check valves 7A and 7A, as well as the flow control valves 6A and 6B to the fork opening operation side hydraulic lines 4A and 4B. 7B, and each pilot operation check valve 7A, 7B allows a backflow (flow in the blocking direction) using the pressure of the fork closing operation side hydraulic pipelines 5A, 5B when contracting the hydraulic cylinders 1A, 1B as pilot pressure. It is supposed to.

That is, when the hydraulic cylinders 1A, 1B are extended in order to increase the distance between the pair of forks 3A, 3B, the pilot operation check is performed by introducing hydraulic pressure into the fork opening operation side hydraulic lines 4A, 4B. The valves 7A, 7B are provided with piston rods 2A,
2B is extended together with the forks 3A, 3B, and the pressure oil in the hydraulic chambers 8A, 8B on the head side is discharged.
A, 3B, each hydraulic cylinder 1A,
When contracting 1B, when hydraulic pressure is introduced into the hydraulic lines 5A and 5B on the fork closing operation side, the pilot operation check valves 7A and 7B are forcibly opened using the pressure as pilot pressure. The pressure oil in the hydraulic chambers 9A, 9B on the cap side of the hydraulic cylinders 1A, 1B is discharged to the fork opening operation side hydraulic lines 4A, 4B.

In FIG. 4, reference numeral 10 denotes a switching valve which is switched by an operation of an attachment operation lever 11 by an operator, and reference numeral 12 denotes a hydraulic pump.

[0007]

In the conventional structure as described above, after adjusting the distance between the forks 3A and 3B, for example, the forks 3A or 3B are removed for some reason.
When an external force F _{A in} a direction that pushes inward is applied,
Each pilot operated check valves 7A, 7B hydraulic backflow fork 3A to prevent, but can be prevented 3B from moving, he joined the direction of the external force F _B that pushes the fork 3A or 3B in opposite outward In this case, since there are no check valves in the hydraulic lines 5A, 5B on the fork closing operation side, the hydraulic chambers 8A, 8A on the head side of the hydraulic cylinders 1A, 1B pass through both hydraulic lines 5A, 5B on the fork closing operation side. The pressure oil flows between the respective forks 3A and 8B, and the forks 3A and 3B move.

As is apparent from FIG. 5, the number of components for realizing the circuit of FIG. 4 is large and the piping layout is complicated. In particular, fork opening operation side hydraulic pipelines 4A and 4B
And the pilot operated check valves 7A, 7A in addition to the pipes 13, 14, which become the hydraulic lines 5A, 5B on the fork closing operation side.
Pilot line 15 for introducing pilot pressure to B
Since the piping 16 serving as A and 15B is attached, the piping 16 is not preferable because it may hinder the operator's front view.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and prevents unnecessary movement of a fork by hydraulically locking a hydraulic cylinder, and also simplifies a piping layout of each hydraulic cylinder. It is an object of the present invention to provide a shift fork device for a forklift, in which the number of parts is reduced and visibility is increased.

[0010]

According to a first aspect of the present invention, there is provided a pair of forks slidably mounted on a carriage, and hydraulic cylinders individually provided on each of the forks. In a forklift shift fork device capable of adjusting the distance between forks by actuating the forks toward and away from each other, the fork opening operation side hydraulic line and the fork closing operation side hydraulic line are independent for each hydraulic cylinder. A pilot operated check valve for locking the hydraulic cylinder is interposed in each of the roads.

According to a second aspect of the present invention, each of the pilot operated check valves according to the first aspect of the present invention is arranged so that the pressure oil is prevented from flowing out from the hydraulic chamber on the head side or the cap side of the hydraulic cylinder. On the other hand, the pilot-operated check valve provided in the fork-opening-operation-side hydraulic line uses the pressure introduced into the fork-closing-operation-side hydraulic line of the same hydraulic cylinder as the pilot pressure, and the fork-closing-operation-side hydraulic line. The pilot-operated check valve provided in the first embodiment is characterized in that it opens the pressure introduced into the fork-opening-operation-side hydraulic pipeline of the same hydraulic cylinder as a pilot pressure, and allows the respective counterflows.

The invention described in claim 3 is the first or second invention.
The two pilot operated check valves attached to each hydraulic cylinder according to the invention described in (1) are characterized by being housed in a common case together with the pilot line and being unitized as one double pilot valve unit.

Therefore, according to the first and second aspects of the present invention, the pilot operation check valve is provided in each of the fork opening operation side hydraulic line and the fork closing operation side hydraulic line connected to each hydraulic cylinder. Therefore, unless the operator operates the attachment operation lever to perform the fork shift operation, that is, the opening or closing operation of the fork interval, each hydraulic cylinder is completely hydraulically locked by the two pilot operation check valves. However, no matter which direction the external force is applied, the fork does not move.

According to the third aspect of the present invention, the two pilot operated check valves to be attached to each hydraulic cylinder are unitized as one valve unit together with the pilot line, so that the required The piping itself is simplified along with the reduction of parts.

[0015]

According to the first and second aspects of the present invention, unless the opening or closing operation of the interval between the pair of forks is actively performed, the hydraulic cylinder for moving the forks is operated by two pilot operations opposite to each other. Because it is hydraulically locked by the stop valve, the fork does not move even if external force is applied to the fork from any direction,
The position reliability of the fork is greatly improved.

According to the third aspect of the present invention, the two pilot operation check valves attached to each hydraulic cylinder are unitized as one valve unit together with the pilot line. Claims 1 and 2 because the number of hydraulic piping elements exposed to the outside is reduced.
In addition to the same effects as those of the invention described in (1), there is an effect that the hydraulic piping system can be simplified by reducing the number of parts and the forward visibility of the operator can be improved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 3 show a preferred embodiment of the present invention, in which parts common to FIGS. 4 and 5 are denoted by the same reference numerals, and FIG. 1 shows an overall schematic configuration.

As shown in FIG. 3, left and right masts 17A,
A guide bar 19 is laid horizontally on the carriage 18 which can be moved up and down along 17B. The guide bar 19 supports a pair of left and right forks 3A and 3B so as to be slidable. Also, the carriage 18
Has a pair of hydraulic cylinders 20 parallel to the guide bar 19.
A and 20B are provided in opposite directions, and the piston rod 21A of one hydraulic cylinder 20A is
A shows the piston rod 21 of the other hydraulic cylinder 20B.
B is connected to the other fork 3B, respectively. By simultaneously extending or contracting the two hydraulic cylinders 20A and 20B, both forks 3A and 3B move apart or approach each other as in the conventional case, and as a result, the distance between the forks 3A and 3B can be arbitrarily set. It can be adjusted. An intermediate portion of each guide bar 19 is supported by a support member 22, and a backrest 23 is mounted above the carriage 18.

FIG. 1 is a diagram showing the details of the hydraulic system of the shift fork device. As is apparent from comparison with FIG. 4, the fork closing operation side hydraulic piping is provided in addition to the fork opening operation side hydraulic lines 4A and 4B. The roads 5A and 5B are different from the conventional ones in that pilot operated check valves 24A and 24B are provided respectively in the paths 5A and 5B. The pilot operation check valves 7A, 7 of the fork opening operation side hydraulic lines 4A, 4B are provided.
B opens the fork closing operation side hydraulic lines 5A, 5B as pilot pressure using the hydraulic pressure introduced into the fork closing operation side hydraulic lines 5A, 5B to allow the flow in the blocking direction.
The pilot operation check valves 24A and 24B of B are connected to the pilot line 25 from the fork opening operation side hydraulic lines 4A and 4B side.
The hydraulic pressure introduced through A, 25B is opened as pilot pressure to allow the flow in the blocking direction.

The hydraulic cylinders 20A, 20B
The pilot operated check valves 7A, 24A and 7B, 24B, which are individually provided two by two, are provided with a common case 26 together with the pilot lines 15A, 25A or 15B, 25B, as is clear from FIG. The double pilot valve unit 27A or 2
It is unitized as 7B.

Therefore, according to the present embodiment, the shift operation of the forks 3A, 3B, that is, the forks 3A, 3B
The operation of adjusting the interval between B is the same as that shown in FIG. 4, but when the switching valve 10 is held at the neutral position as shown in FIG. 1, both the hydraulic cylinders 20A and 20B become pilot operated check valves. 7A, 24A or 7B, 24B will be completely hydraulically locked. For this reason,
Even if an external force acts on the fork 3A or 3B from either the left or right direction, the situation where the forks 3A and 3B move does not occur.

In addition, as apparent from FIG. 2, not only the pilot operated check valves 7A, 7B and 24A, 24B but also the pilot lines 15A, 15B and 25A, 25B to be attached thereto are included. And a single double pilot valve unit 27A, 27
Since it is unitized as B, the piping corresponding to the pilot pipeline is not exposed to the outside as in the conventional case, the piping system is simplified, and the forward visibility of the operator is improved.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of a shift fork device according to the present invention.

FIG. 2 is an exploded perspective view of the piping system of FIG.

FIG. 3 is a perspective view of a main part of the shift fork device mounted on the forklift as viewed from the front.

FIG. 4 is a hydraulic circuit diagram showing an example of a conventional shift fork device.

FIG. 5 is an exploded perspective view of the piping system of FIG.

[Explanation of symbols]

 3A, 3B: Hydraulic cylinder 4A, 4B: Fork opening operation side hydraulic line 5A, 5B: Fork closing operation side hydraulic line 7A, 7B: Pilot operation check valve 8A, 8B: Head side hydraulic chamber 9A, 9B ... Hydraulic chamber on cap side 15B, 15B ... pilot line 18 ... carriage 24A, 24B ... pilot operation check valve 25A, 25B ... pilot line 26 ... case 27A, 27B ... double pilot valve unit

Claims (3)

[Claims] 1. A pair of forks slidably mounted on a carriage, and hydraulic cylinders individually provided on each of the forks, and the forks are moved toward and away from each other by a synchronous operation of the hydraulic cylinders. A pilot operation for locking the hydraulic cylinders in the fork opening operation side hydraulic line and the fork closing operation side hydraulic line, which are independent for each hydraulic cylinder, in the forklift shift fork device in which the distance between the forks is adjustable. A shift fork device for a forklift, wherein a check valve is interposed. 2. The pilot-operated check valve is arranged in a direction for preventing outflow of pressurized oil from a hydraulic chamber on a head side or a cap side of a hydraulic cylinder, and is provided on a fork opening operation-side hydraulic pipeline. The pilot operated check valve uses the pressure introduced into the fork closing operation side hydraulic line of the same hydraulic cylinder as the pilot pressure, and the pilot operated check valve provided on the fork closing operation side hydraulic line is the same hydraulic cylinder fork of the same hydraulic cylinder. 2. The shift fork device for a forklift according to claim 1, wherein the valve is opened as a pilot pressure using the pressure introduced into the opening operation side hydraulic pipeline, and a backflow is permitted to each of the valves. 3. A double pilot valve unit, wherein two pilot operated check valves associated with each hydraulic cylinder are housed in a common case together with a pilot line and are formed as one double pilot valve unit. 3. The forklift shift fork device according to 1 or 2.