JP2000344493A - Forklift truck - Google Patents

Abstract

PROBLEM TO BE SOLVED: To switch the rising speed of a fork to high speed without enlarging a device. SOLUTION: In this forklift truck with each piston cylinder 6 driven for telescopic movement by the operation of switching a control valve 8 so as to raise or lower a fork, a speed selector valve 13 movable between the normal speed side (a) and the high speed side (b) is inserted in hydraulic circuits 12a, 12b which interconnect the control valve 8, a tank 11 to each piston cylinder 6. When the fork is rising, the speed selector valve 13 is moved from the normal speed side (a) to the high speed side (b) whereby pressure oil discharged from the contraction-side chamber 6b of each piston cylinder 6 is mixed with pressure oil supplied from the control valve 8 to the extension-side chamber 6a of the piston cylinder 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forklift capable of switching a fork lifting speed at a high speed.

[0002]

2. Description of the Related Art FIG.
There are the following. This has a pair of outer masts 2 fixed to the front part of the vehicle body 1 and a pair of inner masts 3 supported by the outer masts 2 so as to be able to move up and down.
A fork 5 is attached to an elevating body 4 arranged in the vehicle body, and a pair of hydraulic piston cylinders 6 for elevating the fork 5 via the elevating body 4
And a control valve 8
An operation lever 8a and an operation handle 9 (see FIG. 1) are provided.

[0003] In the above configuration, for example, when unloading a work W stored in the uppermost storage space 10a of the storage shelf 10, the operating lever 8a is switched to extend the piston cylinder 6, thereby driving the piston cylinder 6 to extend. The fork 5 is lifted (see the phantom line in FIG. 4), the body 1 is advanced, the fork 5 is inserted into the pallet P, the fork 5 is slightly raised, and the fork 5 lifts the work W via the pallet P, After the vehicle body 1 is moved backward, the operation lever 8a is switched, whereby the piston cylinder 6 is driven to reduce and lower the fork 5, and the vehicle body 1 travels to transport the work W to a predetermined position. I have.

[0004]

In the above-mentioned conventional configuration,
The fork 5 is lifted and lowered only by the switching operation of the control valve 8, and since the lifting speed is constant, the work W is placed on the fork 5 even when the work W is not loaded on the fork 5 in a no-load state. Is being lifted at the same speed as when it is loaded.

Therefore, it has been demanded that the ascending speed of the fork 5 can be switched from a normal speed to a high speed.
It is conceivable to increase the capacity of a hydraulic pump that supplies pressure oil to the hydraulic pump and increase the driving force of a drive motor that drives the hydraulic pump. However, this increases the size of the apparatus and increases the manufacturing cost.

The present invention has been made in view of the above-mentioned conventional drawbacks, and has as its object to provide a forklift capable of switching the fork lifting speed at high speed without increasing the size of the apparatus.

[0007]

According to a first aspect of the present invention, a fork is attached to an elevating body disposed on a mast on a vehicle body, and the fork is moved up and down through the elevating body. A forklift, wherein a hydraulic piston cylinder is provided on a vehicle body and a control valve provided on an operation unit of the vehicle body is switched to drive the piston cylinder to expand and contract to raise and lower the fork. A speed switching valve that can switch between a normal speed side and a high speed side is interposed in a hydraulic circuit connecting the valve and the tank to the piston cylinder, and when the fork is lifted, the speed switching valve is moved from the normal speed side to the high speed side. , The pressure oil discharged from the reduction side chamber of the piston cylinder is supplied to the control valve. It is characterized in that so as to join the pressure oil supplied to the expansion side chamber Luo piston cylinder.

According to the above configuration, by switching the speed switching valve from the normal speed side to the high speed side, the pressure oil discharged from the reduction side chamber of the piston cylinder is supplied from the control valve to the extension side chamber of the piston cylinder. Therefore, the fork can be raised at a high speed, and the efficiency of the cargo handling operation can be improved. Also, since it is only necessary to add a speed switching valve to the existing hydraulic mechanism,
The equipment does not increase in size and the production cost is low.

According to a second aspect of the present invention, in the first aspect of the present invention, a pressure sensor is interposed in a hydraulic circuit connected to the extension side chamber of the piston cylinder, and the fork is applied to the fork based on an input signal from the pressure sensor. It is characterized in that a control unit is provided for controlling the switching of the speed switching valve to the high speed side only when the load is small.

According to the above construction, the load applied to the fork is detected by the control unit based on the input signal from the pressure sensor, and the switching of the speed switching valve to the high speed side is permitted only when the load is small. Therefore, there is no possibility that the fork is erroneously raised at a high speed in a state where the work is placed on the fork, and an accident due to overload can be prevented beforehand.

[0011] The invention according to claim 3 is the invention according to claim 1 or 2.
In the invention described above, a changeover switch for switching the speed changeover valve is attached to an operation lever of the control valve.

According to the above configuration, the changeover switch of the speed changeover valve can be easily switched while operating the operation lever of the control valve, and the operability is excellent.

[0013]

FIG. 1 shows a main part of a forklift according to an embodiment of the present invention. First and second connecting portions between a control valve 8 and a tank 11 and each piston cylinder 6 are shown. A speed switching valve 13 is interposed in the hydraulic circuits 12a and 12b, and a pressure sensor 1 is connected to a first hydraulic circuit 12a communicating with the extension side chamber 6a of each piston cylinder 6.
4 are interposed. Since the configuration other than the above is almost the same as that shown in FIG. 4, the same portions are denoted by the same reference numerals and description thereof will be omitted.

The control valve 8 has a 6 port 3
The pressure oil discharged from the hydraulic pump 15 is supplied to the tank 11 via the relief valve 16 by operating the operation lever 8a to switch to the left position a.
And the hydraulic oil in the extension side chambers 6a of the piston cylinders 6 is returned to the tank 11 to drive the respective piston cylinders 6 to contract, and the operating lever 8a is operated to switch to the neutral position b, thereby reducing the hydraulic pressure. The pressure oil discharged from the pump 15 is returned to the tanks 11 to fix the piston rods 6c of the piston cylinders 6, and the operation lever 8
a to switch to the right side position c, the hydraulic oil discharged from the hydraulic pump 15 is supplied to each piston cylinder 6.
Are supplied to the extension side chambers 6a to drive the respective piston cylinders 6 to extend. Reference numeral 17 denotes a drive motor for driving the hydraulic pump 15, and reference numeral 18 denotes a check valve.

The speed switching valve 13 is a 4-port 2-position electromagnetic switching valve.
Alternatively, the piston cylinder 6 can be driven to expand and contract at the normal speed by setting the normal speed side a in the state where the piston cylinder 6 is at the right position c.

When the control valve 8 is switched to the high-speed side b with the control valve 8 in the right position c, the pressure oil discharged from the reduction side chamber 6b of each piston cylinder 6 is extended from the control valve 8 to the expansion of each piston cylinder 6. It joins with the pressure oil supplied to the side chamber 6a (see FIG. 3). In this case, since the piston rod 6c is provided in the reduction side chamber 6b and the pressure receiving area of the reduction side chamber 6b is smaller than the pressure receiving area of the expansion side chamber 6a, all the joined pressure oil is supplied to the expansion side chamber 6a. , Piston rod 6c
At a high speed, and the fork can be raised at a high speed.

Here, the inner diameter of the piston cylinder 6 is 45 mm, and the diameter of the piston rod 6c is 35 m.
m, the fork 5 is approximately 1.5 to the normal speed by switching the speed switching valve 13 to the high speed side b.
It can be lifted 1.6 times as fast, and the efficiency of cargo handling can be improved.

According to the above configuration, since the speed switching valve 13 is simply added to the existing hydraulic mechanism, the size of the apparatus is not increased, and the manufacturing cost is reduced.

As shown in FIG. 1, a changeover switch 19 for switching the speed changeover valve 13 is attached to the operation lever 8a.
Only during the state, the speed switching valve 13 is set to the normal speed side a.
To the high-speed side b.

According to the above configuration, the changeover switch 19 can be easily switched while operating the operation lever 8a, and the operability is excellent.

The pressure sensor 14 is connected to the first hydraulic circuit 1
The load applied to the pressurized oil in the extension side chamber 6a of each piston cylinder 6 is detected via the control unit 2 to detect whether or not the work W is placed on the fork 5.

In FIG. 1, reference numeral 20 denotes a control unit comprising a microcomputer provided in the operation unit 7, which controls various devices of the forklift and controls the speed switching valve 13 based on an input signal from the pressure sensor 14. To control.

The control operation of the control section 20 will be described with reference to FIG. 2. With the control valve 8 in the right position b, as shown in step S1, the changeover switch 19
Is pressed to turn it on, as shown in step S2, it is determined whether the load on the fork 5 is small based on the input signal from the pressure sensor 14, and when the load is large, that is, When the work W is placed on the fork 5, the speed switching valve 13 is maintained at the normal speed side a, and when the load is small,
If the fork 5 is not mounted, the process proceeds to step 3, the speed switching valve 13 is switched to the high speed side b (see FIG. 3), and the piston cylinders 6 are extended at a high speed, thereby raising the fork 5 at a high speed.

According to the above configuration, the control unit 20 detects the load applied to the fork 5 based on the input signal from the pressure sensor 14, and switches the speed switching valve 13 to the high speed side b only when the load is small. Since the fork 5 is allowed, there is no danger of the fork 5 being erroneously raised at a high speed with the work W placed on the fork 5, and an accident due to overload can be prevented beforehand.

[0025]

According to the first aspect of the present invention, by switching the speed switching valve from the normal speed side to the high speed side, the pressure oil discharged from the reduction side chamber of the piston cylinder is transferred from the control valve to the extension side chamber of the piston cylinder. The fork can be raised at a high speed, and the efficiency of the cargo handling operation can be improved. Further, since it is only necessary to add a speed switching valve to the existing hydraulic mechanism, the size of the apparatus is not increased, and the manufacturing cost is reduced.

According to the second aspect of the present invention, the control section detects the load on the fork based on the input signal from the pressure sensor, and permits the speed switching valve to be switched to the high-speed side only when the load is small. Therefore, there is no possibility that the fork is erroneously raised at a high speed with the work placed on the fork, and an accident due to overload can be prevented.

According to the third aspect of the invention, the changeover switch of the speed changeover valve can be easily switched while operating the operation lever of the control valve, and the operability is excellent.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing a main part of a forklift according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a control operation of the control unit.

FIG. 3 is a hydraulic circuit diagram of a main part showing a state where the speed switching valve is switched to a high speed side.

FIG. 4 is a side view showing a conventional forklift.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Body 2, 3 Mast 4 Lifting body 5 Fork 6 Hydraulic piston cylinder 6a Extension side chamber of hydraulic piston cylinder 6b Reduction side chamber of hydraulic piston cylinder 8 Control valve 8a Operating lever of control valve 13 Speed switching valve 14 Pressure sensor 19 Switching Switch 20 control unit

Claims (3)

[Claims] 1. A fork is attached to an elevating body disposed on a mast on a vehicle body, and a hydraulic piston cylinder for raising and lowering the fork via the elevating body is provided on the vehicle body, and is provided on an operation unit of the vehicle body. The forklift lifts and lowers the fork by operating the control valve by switching the piston cylinder to expand and lower the fork. In the hydraulic circuit connecting the control valve and the tank to the piston cylinder, a normal speed side and a high speed And a speed switching valve that can be switched between the side and the side.When the fork is lifted, the speed switching valve is switched from the normal speed side to the high speed side, so that the pressure oil discharged from the reduction side chamber of the piston cylinder is discharged. Combine with the pressure oil supplied from the control valve to the extension side chamber of the piston cylinder. A forklift characterized in that: 2. A pressure sensor is interposed in a hydraulic circuit connected to the extension side chamber of the piston cylinder, and switches the speed switching valve to a high speed side only when a load on a fork is small based on an input signal from the pressure sensor. The forklift according to claim 1, further comprising a control unit configured to control the forklift to allow the operation. 3. The forklift according to claim 1, wherein a changeover switch for switching the speed changeover valve is attached to an operation lever of the control valve.