JPH0540079Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a hydraulic cylinder suitable for use as a lift cylinder for a multi-stage mast of a forklift.

[Conventional technology]

As a lift cylinder for a multi-stage mast of a conventional forklift of this type, for example, one shown in FIG. 2 has been developed.

This has a front cylinder 1 and rear cylinders 2, 3, and pressure chambers 4, 5, 6 of the cylinders 1, 2, 3.
are connected to a hydraulic power source 10 via circuits 7, 8, and 9, respectively. Each circuit 7, 8, 9 and hydraulic power source 10
A flow rate control valve 11 and a switching valve 12 are provided midway between the two.

When the switching valve 12 is switched from the neutral position shown in the figure to the left position, high pressure oil from the hydraulic source 10 is transferred to the circuit 7,
8, 9 to the pressure chambers 4, 5, 6 of each cylinder 1, 2, 3, but due to the difference in pressure receiving area of the pistons, the front and rear cylinders 1 expand first, and this front and rear cylinder 1 reaches its maximum extension. After this, the rear cylinders 2 and 3 extend.

When the switching valve 12 is switched from this state to the right position, the pressure chambers 4, 4 of each cylinder 1, 2, 3
5 and 6 are connected to the tank 13 and are lowered one by one by their own weight.

By the way, the front cylinder 1 has a cylinder tube 14 and a piston 15 inside the cylinder tube 14.
and a piston rod 16 movably inserted via a piston ring 15a, pressure chambers 4, 4a partitioned by the piston 15, an oil passage 17 communicating the pressure chambers 4, 4a, and connecting the pressure chamber 4 to the circuit 7. It has a port 18 for connection. The pressure oil supplied from the circuit 7 is introduced into the pressure chamber 4 and
It is also introduced into the pressure chamber 4a via the oil passage 17, but due to the difference in pressure receiving area between the upper and lower surfaces of the piston corresponding to the cross-sectional area of the piston rod 16, the piston rod 1
6 expands. Moreover, near the maximum extension of the piston rod 16, the outlet of the oil passage 17 is gradually constricted by the cylinder tube 14 so that the cushion becomes effective. This prevents the occurrence of shock when switching to extension operation.

[Problem that the invention attempts to solve]

However, since the type of hydraulic cylinder described above has two pressure chambers 4 and 4a above and below the piston, the pressure receiving area acting on the piston is equivalent to the cross-sectional area of the piston rod 16. If this diameter is small, the pushing force will be small. Therefore, in order to increase the pushing force, the diameter of the piston rod can be increased, but in this case, there is a problem that the hydraulic cylinder itself becomes large.

Furthermore, there is a problem in that the oil passage 17 is gradually closed, and when the cushion is activated, the upper pressure chamber 4a becomes high pressure, causing a pressure leak.

Therefore, the purpose of the present invention is to provide a hydraulic cylinder in which the entire cross-sectional area of the piston can be used as a pressure-receiving area, pressure leakage can be prevented as much as possible, and the cushion can be effective during expansion even with only one pressure chamber. The goal is to provide the following.

[Means for solving problems]

In order to achieve the above object, the structure of the present invention is such that a piston rod is movably inserted into a cylinder tube via a piston, and pressure oil is supplied and discharged through a port to a pressure chamber defined at the bottom of the piston. In the cylinder, a guide bar is movably inserted into the piston, the upper part of the guide bar is provided with a locking part that faces the end surface of the piston, and the lower part of the guide bar is a movable spool that opens and closes the port. It is characterized by being inserted freely.

[Effect]

When pressure oil is supplied to the pressure chamber from the port, the piston rod extends through the piston, and when the end surface of the piston comes into contact with the locking part of the guide bar and further extends, the guide bar moves up in conjunction with the guide bar. Along with this, the spool also moves upward, and near the maximum extension, the spool gradually closes the outlet of the port to activate the cushion.

〔Example〕

An embodiment of the present invention will be described below based on FIG.

A hollow piston rod 20 is inserted into the cylinder tube 18 via a hollow piston 19 so as to be vertically movable, a pressure chamber 21 below the piston is defined in the cylinder tube 18, and a central hole 22 of the piston is defined in the piston rod 20. A pressure chamber 24 is defined which communicates with the pressure chamber 21 via the pressure chamber 21 .

Although the chamber 23 above the piston 19 is at atmospheric pressure, this chamber 23 may be omitted.

A guide bar 2 is installed in the center hole 22 of the piston 19.
5 is inserted vertically movably, and this guide bar 2
The upper part of the guide bar 25 extends into the piston rod 20, and the upper part of the guide bar 25 is integrally provided with a locking part 26 made of a horizontal plate.

A buffer member 19a made of a rubber cylinder is arranged on the upper end surface of the piston 19, and faces the locking portion 26. This buffer member 19a may be a spring or other elastic material. This buffer member 19
a may be omitted, and the end surface of the piston is directly connected to the locking part 2.
It may be made to face 6.

Even if the guide bar 25 is inserted into the center of the piston 19, the piston rod 20 is hollow and its upper wall can also be used as a pressure receiving area, so the pressure receiving area in the pressure chamber 21 is eventually equal to the cross-sectional area of the piston 19.

However, if a negative pressure-receiving area corresponding to the cross-sectional area of the guide bar 25 is allowed, the center hole 22 of the piston 19 can be eliminated, a seal is provided here so that the oil chamber 21 becomes an oil chamber, and the guide bar 25 is inserted. let me,
It can also be used even if the chamber 24 is opened to the atmosphere.

An oil chamber 27 communicating with the pressure chamber 21 is defined within the lower bottom 18a of the cylinder tube 18, and a hollow housing 28 is held in the oil chamber 27 via a seal and a screw.

A chamber 29 is defined within the housing 28, and this chamber 29 is open to the pressure chamber 21 and also communicates with the oil chamber 27 via a supply port 30.

A cylindrical spool 31 is provided at the bottom of the guide bar 25.
is inserted so as to be vertically movable, and this spool 31 is urged downward by a spring 32 provided in the chamber 29 and held on the lower flange 33 of the guide bar 25.

When the spool 31 is raised in conjunction with the guide bar 25, the flange 34 is attached to the housing 2 at the maximum extension.
It is adapted to engage with the step portion 35 of No.8.

A discharge port 36 is provided between the oil chamber 21 and the oil chamber 27.
A check valve 37 is provided at the outlet end of the discharge port 36 on the side of the oil chamber 27 so as to be openable and closable.

This check valve 37 is inserted into the outer periphery of the housing 28 so as to be movable up and down, and is locked to a stepped portion provided on the outer periphery of the housing 28 when it is lowered to its lowest position.

A port 38 for supplying and discharging pressure oil is formed in the bottom 18a, and this port 38 selectively connects the oil chamber 27 to a pump or a tank. The configuration of the circuit connected to port 38 is the same as the circuit shown in FIG.

The hydraulic cylinder of the embodiment is suitable for use as a lift cylinder of a forklift, particularly as a front-stage cylinder, for example, as shown in FIG. 2, but it can also be used as a general hydraulic cylinder.

Next, the operation will be described.

When high pressure oil is introduced into port 38, oil chamber 27 - supply port 30 - chamber 29 - pressure chamber 21 - central hole 22 -
is guided to the oil chamber 24 in the piston rod via
The lower surface of the piston 19 and the upper wall of the piston rod 20 act as pressure receiving surfaces, causing the piston rod 20 to extend. At this time, the check valve 37 is pushed up by the pressure in the oil chamber 27, and the discharge port 36 is closed.

When the piston 19 and piston rod 20 are extended nearly to their maximum extension, the buffer member 19a moves toward the guide bar 25.
The guide bar 25 and spool 31 are pulled up in conjunction with the piston, and the outer periphery of the spool 31 gradually closes the outlet of the supply port 30 to activate the cushion. Therefore, sudden shock is prevented from occurring when the piston rod 20 is fully extended.

When lowering the piston rod 20, the supply/discharge port 38 is connected to the tank side. At this time, the spool 31 and the guide bar 25 are pushed back downward by the restoring force of the spring 32, and the piston 19 and the piston rod 20 descend by their own weight. Moreover, pressure chamber 2
The oil in 1 and 24 is returned from the supply port 30, and at the same time, the check valve 37 is pushed open and the oil is returned to the discharge port 3.
It also flows out from 6.

[Effect of idea]

According to the present invention, there are the following effects.

Even if a guide bar is inserted into the piston,
Since this guide bar may be thin, a pressure receiving surface approximately equal to the cross-sectional area of the piston can be obtained, and a desired extension speed can be obtained without increasing the size of the piston. Moreover, when the guide bar extends into the piston rod, the area of the piston end surface becomes a substantial pressure receiving surface.

Since the spool, which is a cushion mechanism, is provided in conjunction with the piston rod and guide bar, the cushion becomes effective near the maximum extension, and the occurrence of shock can be prevented.

Since there is no need to create a pressure chamber to make the cushion effective, pressure leakage from the pressure chamber can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional front view of a hydraulic cylinder according to an embodiment of the present invention, and FIG. 2 is a conventional hydraulic cylinder and its circuit diagram. 18... Cylinder tube, 19... Piston, 20... Piston rod, 21... Pressure chamber,
25... Guide bar, 26... Locking part, 31...
Spool, 38...port.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) A hydraulic cylinder in which a piston rod is movably inserted into a cylinder tube via a piston, and pressure oil is supplied and discharged from a pressure chamber defined at the bottom of the piston via a port. A guide bar is movably inserted into the piston, a locking portion facing an end surface of the piston is provided in the upper part of the guide bar, and a spool for opening and closing the port is movably inserted in the lower part of the guide bar. Hydraulic cylinder. (2) The hydraulic cylinder according to claim 1, wherein the piston rod is formed hollow, and a guide bar passing through the center of the piston is movably inserted into the piston rod. (3) The hydraulic cylinder according to claim 1, wherein the spool is formed into a cylindrical shape and is constantly urged downward via a spring. (4) The hydraulic cylinder according to claim 1 of the utility model registration claim, wherein the port is branched into a supply port and a discharge port, the supply port is opened and closed by a spool, and a check valve is provided in the middle of the discharge port so as to be openable and closable. .