JPH0435356Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a flow control valve for a lift cylinder in a forklift, and more particularly to a flow control valve installed to control the descending speed of the lift cylinder.

(Prior Art) Generally, this type of flow control valve is assembled at the bottom of a lift cylinder 1, as shown in FIG. The flow rate control valve 2 is formed into a cylindrical shape with a bottom, and has a cylinder port 3 communicating with the cylinder chamber 1a on the upper side, and a tank port 5 communicating with the pipe line 4 on the lower side (when the lift cylinder 1 is raised, A valve body 6 is provided with a valve body 6 (which becomes a pump port), and a valve body 6 is fitted into the valve body 6 so as to be movable up and down, and has a through hole 7 that communicates with the cylinder port 3. A piston valve 8 formed in the above-mentioned shape, a balance spring 9 that always biases the piston valve 8 upward, and a balance spring 9 that is attached to the open upper end of the valve body 6, and is attached to the peripheral wall of the valve body 6 and the upper end surface of the piston valve 8. A lid plate 11 forming a pressure chamber 10 and a pressure chamber 10 inside this pressure chamber 10.
and a check valve 13 installed in correspondence with a passage 12 formed in the center of the cover plate 11 to communicate between the lift cylinder 1 and the cylinder chamber 1a, and when the lift cylinder 1 is lowered, the cylinder side pressure is The piston valve 8 is moved by the differential pressure between the cylinder pressure and the tank side pressure to limit the amount of hydraulic oil flowing out from the cylinder chamber 1a.

That is, the piston valve 8 receives the cylinder side pressure of the hydraulic oil that flows into the pressure chamber 10 from the cylinder chamber 1a via the check valve 13 and acts on the upper surface of the piston valve 8, and the pressure on the lower surface of the piston valve 8 within the valve body 6. The oil is pushed down by the differential pressure between the tank side pressure and the opening of the tank port 5, thereby limiting the amount of oil flowing out to the tank side and controlling the descending speed of the lift cylinder 1. The amount of throttling at this time is determined by the balance between the differential pressure and the pushing up force of the balance spring 9.

In addition, when the lift cylinder 1 is raised,
Since the piston valve 8 is held at the upper end position as the original position by the balance spring 9, the hydraulic oil supplied by the hydraulic pump is sent to the cylinder chamber 1a without being subjected to the throttling action by the flow control valve 2. Such a type of flow control valve is disclosed in, for example, Japanese Utility Model Application No. 56-92700.

(Problem to be solved by the invention) However, in the case of the above-mentioned flow rate control valve 2, the balance spring 9 for opening control, which determines the position of the piston valve 8, is replaced by a return spring that returns the piston valve 8 to its original position. Since the system is designed to function as a hydraulic oil return circuit, the spring resistance when the piston valve 8 starts moving is large when the hydraulic oil return circuit is opened, so the differential pressure required to move the piston valve 8 is large. It took a long time for this to occur, and during that time it was not possible to properly control the flow rate. That is, in the conventional flow control valve 2, there was a problem in that there was a delay in operation when the lift cylinder 1 started to descend, causing the fork to suddenly descend.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an improved flow control valve for a lift cylinder in order to solve the above-mentioned conventional problems.

(Means for Solving the Problems) The present invention for solving the above problems includes a valve body having a cylinder port and a tank port, a valve body that is movably fitted into the valve body, and a cylinder side and a tank side. a piston valve that moves according to the differential pressure to control the amount of oil flowing out from the tank port; a balance spring that holds the piston valve in a position balanced with the differential pressure to control the opening degree of the tank port; and a piston valve. A flow control valve for controlling the amount of hydraulic oil flowing out when the lift cylinder is lowered is configured by a return spring having a weaker force than the balance spring for returning the lift cylinder to its original maximum opening position. The gist is:

(Function) Therefore, when the circuit connecting the lift cylinder and the tank is connected to lower the lift cylinder,
Immediately after the lift cylinder starts its downward movement, the piston valve compresses a weak return spring by the differential pressure between the cylinder side pressure and the tank side pressure, that is, the differential pressure that acts on the upper and lower sides of the piston valve. By moving while moving, the opening of the tank port is narrowed and the sudden outflow of hydraulic oil is suppressed. Thereafter, the balance spring acts on the piston valve to maintain the piston valve at a position where its pressing force and the differential pressure are balanced, thereby controlling the amount of oil flowing out to the tank side.

(Example) Hereinafter, an example of the present invention will be specifically described based on FIGS. 1 and 2. Fig. 2 shows an example of the hydraulic circuit of the lift cylinder 1 in a battery type forklift.
The hydraulic oil pumped up from the tank 18 by the hydraulic pump 17 is supplied to the lift cylinder 1 through the check valve 19 and the flow control valve 2 built into the bottom of the lift cylinder 1. To lower the cylinder 1, the solenoid valve 20 is switched to the open side, and the hydraulic oil in the lift cylinder 1 is pumped into the tank 18 at a flow rate limited by the flow rate control valve 2.
This is now being done by returning to

The flow rate control valve 2, which functions to keep the speed of descent constant when the lift cylinder 1 is lowered, is constructed as shown in FIG. However, the same reference numerals are given to the same constituent members as in the conventional case, and the explanation thereof will be omitted. As shown in the figure, in this embodiment, a ring-shaped spring guide 14 with edges is fitted to the inner peripheral surface of the lower side of the piston valve 8 so as to be movable up and down, and this spring guide 14 and the inside of the piston valve 8 A return spring 15 is interposed between the shoulder portion 8a and the shoulder portion 8a.
The spring guide 14 is supported by a balance spring 9. The pressing force of the return spring 15 is much weaker than that of the balance spring 9, and is set to such an extent that the piston valve 8 can be returned to its original upper end position against its own weight. On the other hand, the length of the balance spring 9 is set so that it is in a free state when the piston valve 8 is in its original position.

This embodiment is configured as described above,
Therefore, when the electric motor 16 is driven to raise the lift cylinder 1, the hydraulic oil pumped up by the hydraulic pump 17 is supplied from the check valve 19 to the cylinder chamber 1a via the flow control valve 2. Raise the piston rod 1A. At this time, the piston valve 8 of the flow control valve 2 is held in the raised position by the return spring 15, so that the hydraulic fluid is sent to the cylinder chamber 1a without being subjected to the throttling action of the flow control valve 2.

On the other hand, in order to lower the lift cylinder 1, the solenoid valve 1
9 is switched to the passage open side, the hydraulic oil in the cylinder chamber 1a flows out from the cylinder port 3 of the flow rate control valve 2 through the through hole 7 and the tank port 5 to the tank 18, but at this time, the cylinder The hydraulic oil in the chamber 1a pushes open the check valve 13 in the flow control valve 2, flows into the pressure chamber 10, and acts on the upper surface of the piston valve 8. Since this pressure is greater than the pressure acting on the lower surface of the piston valve 8 in the valve body 6 that communicates with the tank side, the piston valve 8 is pushed down by the differential pressure and the tank port 5 is throttled. The movement of the piston valve 8 at this time is performed against the return spring 15, but as described above, the return spring 15 has a weak force that counters the weight of the piston valve 8.
The piston valve 8 moves quickly to throttle the tank port 5 and limit the amount of oil flowing out, so the lift cylinder 1
Immediately after the start of the descending operation, the descending speed is controlled without sudden descent.

Note that when the return spring 15 is compressed, the shoulder 8a of the piston valve 8 comes into contact with the edge 14a of the spring guide 14, and is then placed under the control of the balance spring 9, so the piston valve 8 responds to the differential pressure. It stops at a position where the balance spring force and balance spring force are balanced. Therefore, the hydraulic oil flows out at a flow rate corresponding to the opening degree of the tank port 5 determined by the stop position of the piston valve 8, and the lowering speed of the lift cylinder 1 is controlled.

Next, the embodiment shown in FIG. 3 will be described. In this embodiment, the positions of the return spring 15 and balance spring 9 are changed.
That is, the return spring 15 is disposed on the lower side of the valve body 6 via the spring guide 14, and the other configurations are the same as those of the previous embodiment. Therefore, in this embodiment, as in the previous embodiment, it is possible to compress the return spring 15 first, immediately after the lift cylinder 1 starts lowering, so that the piston valve 8 can quickly throttle the tank port 5. It is possible.

Note that this example uses the electric motor for driving the pump.
The explanation was given for the lift cylinder of a battery type forklift that raises the lift cylinder by ON/OFF control, but the lift cylinder of the engine vehicle, that is, the hydraulic pump is constantly driven, and the oil control valve is switched and operated to raise the lift cylinder. It may also be applied to lift cylinders that are capable of raising and lowering.

(Effects of the invention) As detailed above, according to the invention, the flow rate control valve is provided with a return spring that returns the piston valve to its original position and a balance spring that balances the pressure. Since the spring force for the return of the piston valve can be set to the minimum necessary, it is possible to quickly control the outflow of hydraulic oil when the lift cylinder is lowered, and prevent the fork from descending suddenly. Therefore, it is possible to prevent the cargo from collapsing due to the sudden descent of the fork, thereby contributing to the safety of cargo handling operations.

[Brief explanation of the drawing]

Fig. 1 is a vertical sectional view of a flow control valve assembled to a lift cylinder showing an embodiment of the present invention, Fig. 2 is a hydraulic circuit diagram for operating the lift cylinder, and Fig. 3 is a flow control valve of another embodiment. FIG. 4 is a vertical cross-sectional view showing a conventional example. 1...Lift cylinder, 2...Flow control valve, 3
...Cylinder port, 5...Tank port, 6...
... Valve body, 8 ... Piston valve, 9 ... Balance spring, 14 ... Spring guide, 15 ...
return spring.

Claims (1)

[Scope of utility model registration request] This is a flow control valve that controls the amount of hydraulic oil that flows out when the lift cylinder is lowered, and includes a valve body equipped with a cylinder port and a tank port, and a valve body that is movably fitted into the valve body and has two ports on the cylinder chamber side and the tank side. a piston valve that moves based on the differential pressure between the piston and the tank port to control the amount of oil flowing out from the tank port; a balance spring that holds the piston valve in a position that balances the differential pressure and controls the opening degree of the tank port; A flow control valve for a lift cylinder, comprising a return spring having a weaker force than the balance spring for returning the valve to its original maximum opening position.