JPH0227280B2 - FUOOKURIFUTONORIFUTOKAIRO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lift circuit for a cylinder for lifting and lowering cargo in a large forklift.

Large forklifts are mainly used in ports for handling heavy goods such as containers.
Efficient work is desired in line with ship operation, and the lifting speed of the lift cylinder in particular has a big impact on work efficiency, and it is necessary to make the lifting speed as fast as possible, so hydraulic pumps are used for this purpose. However, in order to flow a large flow of pressure oil under high load, the horsepower of the engine driving the hydraulic pump must be increased, and the engine must be larger than necessary for the vehicle. It will be equipped with.

Therefore, when the load is light when unloaded, a hydraulic pump with a large flow rate is used to increase the rising speed, and when the load is high when loaded, the flow rate of the hydraulic pump is reduced to slow the rising speed. Therefore, a vehicle that can be used safely is desired. For this reason, conventional methods have been considered to divert part of the flow rate of the hydraulic pump or to divide the flow using multiple hydraulic pumps, but due to the large flow rate, it is difficult to control with a normal spool valve, and it is complicated. However, there are disadvantages such as the fact that it becomes a mechanism and becomes extremely costly.

The present invention is a forklift lift circuit developed in view of the above-mentioned circumstances, in which a first pump is connected to a directional control valve of a lift cylinder by a conduit through an outlet of a first poppet valve. A second pump is connected to both the inlets of the first poppet valve and the second poppet valve, and the outlet of the second poppet valve is connected to a tank circuit, and the rear chamber of the second poppet valve is connected to the tank circuit. It is characterized in that a pilot switching valve is provided to switch between the second pump and the tank circuit, and a pilot circuit is connected from the pipeline to the rear chamber of the first poppet valve and the pilot valve. By using two pumps and a poppet valve, the oil volume of both pumps is combined and used when the load is light, and the oil volume of one pump is automatically used when the load is high. The object of the present invention is to provide a lift circuit for a forklift that eliminates the above-mentioned drawbacks.

The present invention has the above-mentioned configuration, and when the load applied to the lift cylinder is light, the pressure oil on the first pump side is lifted via the outlet of the first poppet valve, the piping, and the directional control valve. At the same time, the oil pressure in the pipeline does not become particularly high and the pressure oil on the second pump side is added to the rear chamber of the second poppet valve, closing the second poppet valve. The side pressure oil opens the first poppet valve and the first poppet valve opens.
It merges with the pressure oil on the pump side and becomes a large flow rate, which is supplied to drive the lift cylinder, allowing the lift cylinder to be driven at high speed.When the load applied to the lift cylinder is high, the oil pressure in the piping increases and the oil pressure increases. When the pilot pressure reaches the pilot pressure, the pilot switching valve is automatically switched via the pilot circuit, the second poppet valve is opened, the first poppet valve is closed, and the pressure oil on the second pump side switches the second poppet valve. Since the pressure oil is bypassed to the tank circuit through the pump, only the pressure oil on the first pump side is supplied for driving the lift cylinder, and the lift cylinder is driven at a low speed, and the switching is automatically performed. As a result, the drive performance and reliability of the lift cylinder are significantly improved.

Furthermore, in the present invention, when the pressure oil of the first pump and the second pump are flowing together at a large flow rate, the pressure oil of the first pump is limited by the pilot switching pressure.
The pump and the second pump are driven at relatively low pressure, and when the flow rate of only the pressure oil on the first pump side is small, they can be driven at high pressure up to the set pressure, and the output of the engine for driving both pumps is reduced. It can be used effectively and there is no need to increase its output more than necessary, saving equipment costs and power.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which 1 is a first hydraulic pump, 2 is a second hydraulic pump, and 20 is a first hydraulic pump.
is an engine for driving both the pumps 1 and 2, and the first hydraulic pump 1 is connected to the first hydraulic pump via a pipe line 10.
It is connected to the outlet of the poppet valve 3, and can be switched and connected from the outlet to the lift cylinder 8 and the tank via the conduit 11 and the directional control valve 7, while the second hydraulic pump 2 Conduit 9
is connected to both the inlets of the first poppet valve 3 and the second poppet valve 4, and the outlet of the second poppet valve 4 is connected to the tank circuit 16, and the back chamber 41 of the second poppet valve 4 is connected to the second hydraulic pump 2 side through pilot circuits 13 and 14 in which a pilot switching valve 5 is interposed, and is connected to a tank circuit 16.

Further, a pilot circuit 12 is connected between the pipe line 11, the rear chamber 31 of the first poppet valve 3, and the pilot portion 51 of the pilot switching valve 5. In addition, 6 in the figure is a relief valve of the pipe line 11.

The embodiment of the present invention has the above-mentioned configuration, and to explain the operation and effect, in the state shown in FIG. By-passing the outlet, line 11 and directional valve 7 to the tank is provided. On the other hand, the pressure oil on the second hydraulic pump 2 side reaches both the inlets of the first poppet valve 3 and the second poppet valve 4 through the pipe line 9, but the pressure oil does not reach the pilot circuit 1.
4. Pilot switching valve 5 and pilot circuit 1
3 to the rear chamber 41 of the second poppet valve 4, the second poppet valve 4 is not opened.
The first poppet valve 3 is opened, and the oil is sent through the conduit 11 to the directional control valve 7 and merges with the pressure oil on the first pump 1 side. Therefore, when the load applied to the lift cylinder 8 is light, when the directional control valve 7 is switched to, for example, the lift cylinder up position, the lift cylinder 8
The pressure oil from both the first pump 1 and the second pump 2 is combined and sent to lift the lift cylinder 8 at high speed.
In other words, the forks can be raised and cargo handling efficiency can be improved.

In addition, when the lift cylinder 8 is under a high load due to cargo, the directional control valve 7
When the lift cylinder 8 is placed in the raised position, the pressure in the pipe line 11 increases due to the high load on the lift cylinder 8, and this high pressure is sent from the pilot circuit 12 to the pilot switching valve 5 as pilot pressure.
This force is overcome and the pilot switching valve 5 is automatically switched to the position shown in FIG. At this time, the rear chamber 41 of the second poppet valve 4 is communicated with the tank circuit 16 via the pilot switching valve 5, so the second poppet valve 4 is opened by hydraulic pressure from the pipe line 9, and the second hydraulic pump The pressure oil on the second side becomes a flow that is bypassed to the tank circuit 16, and at the same time, the high pressure from the pilot circuit 12 is communicated to the rear chamber 31 of the first poppet valve 3. It is closed by pressure to prevent the pressure oil on the first hydraulic pump 1 side from flowing backward. Therefore, the pressure oil sent to the directional switching valve 7 has a flow rate only on the first hydraulic pump 1 side, and the lift cylinder 8 and fork can be driven (raised) at low speed.

Therefore, when lifting the lift cylinder 8 under a light load such as an empty load, the flow rates of pressure oil from the first hydraulic pump 1 and the second hydraulic pump 2 are automatically combined and supplied to the lift cylinder 8. As a result, the lift cylinder, that is, the fork, can be raised efficiently at high speed, improving work efficiency. In addition, when the load is high, the pressure oil on the second hydraulic pump 2 side is bypassed to the hydraulic tank side, so the second hydraulic pump 2 side is bypassed to the hydraulic tank side. 1 The flow rate only from the hydraulic pump 1 side is sent to the lift cylinder 8, and the load is safely raised at low speed.

Moreover, when a large flow rate flows at the time of the above-mentioned merging,
The first and second hydraulic pumps 1 and 2 are driven at low pressure, limited by the switching pressure of the pilot switching valve 5, and when only the first hydraulic pump 1 has a small flow rate, the setting of the relief valve 6 Since the engine is driven at a high pressure up to the maximum pressure, the pressure of the engine 20 is used effectively and there is no need to install an engine that is larger than necessary.

If the first and second poppet valves 3, 4 and the pilot switching valve 5 are arranged in parallel, the number of hydraulic pumps can be increased to make it possible to switch the flow rate in three or more stages.

Although the present invention has been described above with reference to embodiments, it goes without saying that the present invention is not limited to these embodiments, and can be modified in various ways without departing from the spirit of the present invention.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a lift circuit showing an embodiment of the present invention, and FIG. 2 is a usage diagram of FIG. 1. 1: First pump, 2: Second pump, 3: First poppet valve, 4: Second poppet valve, 5: Pilot switching valve, 7: Directional switching valve, 8: Lift cylinder,
11: Conduit, 12, 14, 14: Pilot circuit, 31, 41: Back chamber.

Claims (1)

[Claims] 1. A first pump is connected to the directional control valve of the lift cylinder by a conduit through the outlet of the first poppet valve, and a second pump is connected to the inlets of both the first poppet valve and the second poppet valve. At the same time, the second
A pilot switching valve is provided which connects the outlet of the poppet valve to a tank circuit, and switches the back chamber of the second poppet valve to the second pump and the tank circuit, and connects the back chamber of the first poppet valve from the pipe line to the tank circuit. and a forklift lift circuit, characterized in that a pilot circuit is connected to the pilot valve.