JPH1036099A - Lifting speed shifting device for forklift - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable switching the lifting speed of a lift cylinder between two of high and low speeds using a single hydraulic pump. SOLUTION: In a device for switching the lifting speed of a forklift, a twist lock switch 4 is used to detect whether or not there is a container C, and a solenoid switching valve 12 is switched accordingly to communicate the rod chamber 2b of a lift cylinder 2 with either a bottom chamber 2a or an oil tank 9. Therefore, when pressure oil from a hydraulic pump 6 is supplied to the bottom chamber 2a of the lift cylinder 2 by operating an oil control valve 7, flow fed into the bottom chamber 2a varies, so that the rising speed of the lift cylinder 2 is switched between two of high and low speeds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lift speed switching device for a forklift, and more particularly to a lift speed switching device suitable for a forklift having a spreader for loading and unloading containers as a device for loading a load.

[0002]

2. Description of the Related Art Conventionally, as this kind of lift speed switching device, there is, for example, Japanese Utility Model Laid-Open No. 61-44496. The lift speed switching device disclosed in the above publication includes first and second two hydraulic pumps driven by an engine, and pressure oil discharged from the first hydraulic pump is supplied to a container via an oil control valve. The hydraulic fluid is sent to a lift cylinder for raising and lowering the spreader, and the pressure oil discharged from the second hydraulic pump is sent to an oil control valve or an oil tank by a switching valve. In addition, the presence or absence of the container is detected by the switch attached to the container spreader,
When the container is loaded, the switching valve is switched to a position for returning the hydraulic oil from the second hydraulic pump to the oil tank, and when empty, the switching valve is switched to a position for transmitting the hydraulic oil from the second hydraulic pump to the oil control valve. I have.

[0003] Therefore, when the container is loaded, the pressure oil discharged from the second hydraulic pump is returned to the tank, so that the lift cylinder is raised at a speed corresponding to the amount of pressure oil sent from the first hydraulic pump. On the other hand, the second
Hydraulic oil discharged from the first hydraulic pump merges with the hydraulic oil discharged from the first hydraulic pump and is sent to the lift cylinder. Therefore, the lift cylinder operates at a speed corresponding to the oil supply amount of both pumps, that is, when the container is loaded. Be raised faster than.

[0004]

According to the lift speed switching device as described above, the lift cylinder can be raised at the time of unloading at a higher speed than at the time of loading at the time of loading and unloading the container. It is effective in aiming at. However, since the absolute flow rate is increased by using two hydraulic pumps, there is a problem in that the oil control valve, piping, and the like must be increased in size.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a forklift lift capable of switching the lift speed of a lift cylinder between high and low stages using a single hydraulic pump. It is to provide a speed switching device.

[0006]

Means for Solving the Problems In order to solve the above problems, the present invention is configured as follows. That is, the invention of claim 1 is a lift speed switching device of a forklift, wherein the lift speed switching device is provided in a circuit connecting a lift cylinder, a single hydraulic pump, a bottom chamber of the lift cylinder and the hydraulic pump, and An oil control valve for controlling the supply and discharge of pressurized oil to and from the cylinder, a load detecting means for detecting the presence or absence of a load, and a switching operation performed by an output signal of the load detecting means. A switching valve communicating with the bottom chamber and connecting the rod chamber of the lift cylinder to the oil tank for a signal indicating that there is a cargo is provided.

According to the first aspect of the present invention, when a load is loaded on the loading device, the switching valve moves the rod chamber of the lift cylinder to the oil tank based on a signal from the load detecting means. Communicate with Therefore, if the oil control valve is operated in this state, the pressure oil discharged from the hydraulic pump is sent to the bottom chamber of the lift cylinder, and the pressure oil in the rod chamber is returned to the oil tank. Is increased at a speed corresponding to the amount of oil supplied.

On the other hand, when no load is loaded on the loading device, the switching valve communicates the rod chamber of the lift cylinder with the bottom chamber based on a signal from the load detecting means to form a differential cylinder circuit. When the oil control valve is operated in this state, the return oil in the rod chamber merges with the pressure oil discharged from the hydraulic pump and is sent to the bottom chamber of the lift cylinder, and the lift cylinder is raised at a higher speed than during loading. You.

[0009]

Embodiments of the present invention will be specifically described below with reference to the drawings. This embodiment is applied to a forklift provided with a container spreader for loading and unloading containers as shown in FIG. The container spreader 3 is attached to the mast 1 so as to be able to move up and down. The twist lock pin 4 is inserted from above into a suspension hole formed on the upper surface of the container C, and is locked by rotating about its axis. In this state, the container is lifted by the lift cylinder 2 to lift the container.

FIG. 1 shows a lift speed switching device of a forklift. In this embodiment, a single hydraulic pump 6 driven by an engine 5 is provided, and pressure oil discharged from the hydraulic pump 6 is sent to an oil control valve 7 operable by an operator. I have. The oil control valve 7 is a three-position switching valve, and is always held at the illustrated neutral position by a spring. In FIG. 1, reference numeral 8 denotes a filter provided at the suction port of the suction pipe, and reference numeral 9 denotes an oil tank.

The oil control valve 7 and the bottom chamber 2 a of the lift cylinder 2 are connected by a pressure oil supply / discharge pipe 10. Further, the bottom chamber 2a and the rod chamber 2b of the lift cylinder 2 are connected by a communication pipe 11, and
The connecting pipe 11 is provided with a two-position solenoid-operated switching valve 12 for switching between connecting the rod chamber 2 b to the bottom chamber 2 a or connecting the rod chamber 2 b to the oil tank 9 via the return pipe 13.

The electromagnetic switching valve 12 is switched based on an on / off signal of a twist lock switch 14 serving as a cargo detecting means. The twist lock switch 14 is actuated by a rotational displacement of the twist lock pin 4 of the container spreader 3 around the axis,
It is turned off by turning to the locking position with respect to the suspension hole, and turned on by turning to the unlocking position. The electromagnetic switching valve 12 connects the rod chamber 2b to the bottom chamber 2a when the twist lock switch 14 is turned on, and returns the rod chamber 2b to the pipe line 1 when the twist lock switch 14 is turned off.
Communicate with 3.

Next, the operation and effect of the lift speed switching device according to the embodiment configured as described above will be described. When loading the container of the container spreader 3, the twist lock pin 4 is rotated to the locking position. for that reason,
The twist lock switch 14 is turned off, and the electromagnetic switching valve 12 is switched to a position where the rod chamber 2 b communicates with the return pipe 13.

Therefore, when the oil control valve 7 is switched to the raised position in this state, the pressure oil sent from the hydraulic pump 6 is sent to the bottom chamber 2a of the lift cylinder 2, and the return oil of the rod chamber 2b is sent to the bottom chamber 2a. The oil is discharged to the oil tank 9 via the return pipe 13. Therefore, lift cylinder 2
Is increased at a speed corresponding to the supply amount of the pressure oil fed from the hydraulic pump 6.

On the other hand, when the container spreader 3 is empty, the twist lock pin 4 is turned to the unlocking position, so that the twist lock switch 14 is turned on, and the electromagnetic switching valve 12 closes the rod chamber 2b of the lift cylinder 2. The differential cylinder circuit is configured by being switched to a position communicating with the bottom chamber 2a. Therefore, when the oil control valve 7 is switched to the raised position in this state, the return oil from the rod chamber 2b joins the pressure oil sent from the hydraulic pump 6 and is supplied to the bottom chamber 2a. 2
Is raised at a higher speed than when the container is loaded. In addition,
Although the above description is for the case of ascending, also in the case of descending, as in the case of ascending, the descending speed when empty is performed at a higher speed than when loading luggage.

As described above, according to the present embodiment, the rod chamber 2b of the lift cylinder 2 is communicated with the oil tank 9 or the bottom chamber 2a by switching the electromagnetic switching valve 12 in accordance with the presence or absence of the container. 2 bottom chamber 2
Since the lift speed of the lift cylinder 2 can be switched between high and low by changing the amount of pressurized oil supplied to a, the problem of the conventional method of increasing the absolute flow rate using two hydraulic pumps is used. That is, it is possible to solve the problem of scale-up of the hydraulic equipment such as an increase in the size of the oil control valve and the piping.

In general, the pressure in the bottom chamber 2a of the lift cylinder 2 is high during loading and low when empty. Therefore, as a form for detecting the presence / absence of a container, it is conceivable to use a pressure switch that is turned on / off by a pressure change in the bottom chamber 2a of the lift cylinder 2 during loading and emptying. However, in the case of such a pressure detection method, when the rod chamber 2b is communicated with the bottom chamber 2a, the pressure in the bottom chamber 2a rises at the same level as when loading, and it is difficult to obtain a stable switching function. However, in this embodiment, since the mechanical displacement of the twist lock pin 4 is electrically detected as the presence or absence of the container, a stable switching function is obtained, and the operation of the electromagnetic switching valve 12 switched based on the switching function is also stabilized. .

[0018]

As described in detail above, according to the present invention,
The lift speed of the lift cylinder can be switched between high and low by switching between communicating the rod chamber of the lift cylinder with the bottom chamber or communicating with the oil tank in accordance with the presence or absence of a load. Therefore, there is no need to increase the absolute flow rate of the hydraulic circuit, and the problem of scale-up of hydraulic equipment is eliminated.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing a lift speed switching device according to the present embodiment.

FIG. 2 is a schematic side view of a forklift provided with a container spreader.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Mast 2 ... Lift cylinder 3 ... Container spreader 6 ... Hydraulic pump 7 ... Oil control valve 11 ... Communication line 12 ... Electromagnetic switching valve 14 ... Twist lock switch

Claims (1)

[Claims] A lift cylinder, a single hydraulic pump, an oil control valve provided in a circuit connecting the bottom chamber of the lift cylinder and the hydraulic pump, and controlling supply and discharge of pressurized oil to and from the lift cylinder. A load detecting means for detecting the presence or absence of a load, and a switching operation is performed by an output signal of the load detecting means. In a signal of no load, the rod chamber of the lift cylinder communicates with the bottom chamber. A lift speed switching device for a forklift, comprising a switching valve for communicating a rod chamber with an oil tank.