JP2000205207A - Internal drain type lift cylinder - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce the number of processing steps and cost at the time of manufacturing an internal drain type lift cylinder, and to improve the strength of a piston rod together with these. SOLUTION: When the hydraulic oil leaking from a hydraulic oil chamber 18 to a portion 20 between two oil seals 15 and 16 provided on a sliding surface of a piston 5 reaches a predetermined storage pressure, the leaked oil is removed. In order to return to the hydraulic oil chamber 18, a portion 20 between the oil seals 15 and 16 is communicated with the hydraulic oil chamber 18 by a return oil path 21 provided in the piston 5. Check valve 2 with relief function
2 is interposed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal drain type lift cylinder suitable for use as a hydraulic cylinder for unloading and unloading cargo in industrial vehicles such as forklifts and crane trucks.

[0002]

2. Description of the Related Art Conventionally, as an internal drain type lift cylinder of this type, for example, one disclosed in Japanese Patent Application No. 122205/1998, which was published on May 12, 1998, is disclosed. It has been known.

That is, in this apparatus, a reservoir chamber is formed in a piston rod in communication with a rod-side oil chamber, and compression of an upper gas caused by a reduction in the volume of the rod-side oil chamber accompanying extension of a lift cylinder is performed by a piston rod. Compensate with a reservoir chamber formed within.

[0004] When the pressure in the reservoir chamber becomes too large, the relief valve is pushed open to release the pressure to the hydraulic oil chamber, whereby the sliding of the cylinder cap, which is the guide portion of the piston rod, is performed. Problems such as the oil seal interposed on the surface coming off are prevented.

[0005]

As a result, in the conventional internal drain type lift cylinder described above, it is necessary to form a hollow reservoir chamber inside the piston rod. In addition to the increase in the number of processing steps and the increase in cost, there is a problem that the cross-sectional area of the piston rod in the portion of the reservoir chamber is reduced and the strength tends to be insufficient.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to eliminate a hollow portion as a reservoir chamber formed inside a piston rod, thereby reducing the number of processing steps and costs, and in addition to these, the strength of the piston rod. It is an object of the present invention to provide an internal drain type lift cylinder of this kind which can be improved.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a hydraulic pressure control apparatus in which hydraulic oil leaking from a hydraulic oil chamber to a portion between two oil seals provided on a sliding surface of a piston has a predetermined pressure. In order to return the leaked oil to the hydraulic oil chamber when the pressure reaches the oil oil chamber, the portion between these two oil seals is communicated with the hydraulic oil chamber through a return oil path provided in the piston, and This is achieved by interposing a check valve having a relief function.

That is, by configuring as described above,
When the hydraulic oil leaking from the hydraulic oil chamber to the portion between the two oil seals in the piston reaches a predetermined accumulated pressure without forming a hollow reservoir chamber inside the piston rod, the leakage occurs. The oil is returned from the portion between the two oil seals to the hydraulic oil chamber side while pushing open the check valve having a relief function through a return oil passage provided in the piston directly.

This eliminates the need to form a hollow reservoir chamber for the piston rod.
Not only can the number of processing steps and cost be reduced, but also the strength of the piston rod can be improved.

Further, instead of providing the return oil passage provided with the check valve having a relief function for the piston as described above, the oil seal located on the hydraulic oil chamber side of the two oil seals provided on the piston. Can also be achieved by interposing in the direction in which the lip opens with the accumulated pressure from the rear side.

This is because even in this case, the hydraulic oil leaked from the hydraulic oil chamber to the portion between the two oil seals in the piston without forming a hollow reservoir chamber inside the piston rod. When the pressure reaches a predetermined accumulated pressure, the leaked oil is returned to the hydraulic oil chamber while the lip of the oil seal on the hydraulic oil chamber side provided on the piston is pushed and expanded by the accumulated pressure.

Therefore, it is not necessary to perform special processing not only on the hollow reservoir chamber for the piston rod but also on the piston, so that the number of processing steps and cost can be further reduced along with the improvement of the strength of the piston rod. It can be planned.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. 1 and 2 shown in the accompanying drawings.

In FIG. 1, an internal drain type lift cylinder 1 according to the present invention has a cylinder tube 4 closed at both ends by a cylinder bottom 2 and a cylinder head 3, and is slidably inserted into the cylinder tube 4. The main part is constituted by a piston 5 and a piston rod 6 slidably extending from the piston 5 to the outside through the cylinder head 3.

In the above description, the joint between the piston 5 and the piston rod 6 is formed by fitting a small diameter projection 7 formed on the upper part of the piston 5 into a fitting part 8 formed on the lower end of the piston rod 6, and A stop screw 10 is screwed and connected to the formed annular groove 9 from the outer peripheral surface of the piston rod 6.

The coupling means in this case is not limited to the coupling means using the annular groove 9 and the stopper screw 10, but as shown in another embodiment of FIG. The two may be connected to each other by fitting the ring stopper 12 into the annular groove 11 extending between the piston rod 6 and the fitting portion 8 of the piston rod 6.

On the other hand, the piston 5 comes into sliding contact with the inner wall surface of the cylinder tube 4 via a bearing 13 provided on the outer peripheral surface, and the piston rod 6 moves to a bearing 14 fitted on the inner wall surface of the cylinder head 3. By sliding contact, the bearing 13,
Through 14, the inside of the cylinder tube 4 is smoothly extended and contracted.

Furthermore, two oil seals 15, 1 with a bearing 13 interposed therebetween are provided on the outer peripheral surface of the piston 5.
In addition, a dust seal 17 is provided at the upper end of the cylinder head 3 in sliding contact with the outer peripheral surface of the piston rod 6, and the interior of the cylinder tube 4 is moved by the piston 5 through these oil seals 15 and 16. It is divided into a lower working oil chamber 18 and an upper gas chamber 19.

The piston 5 is provided with a return oil passage 21 for guiding a portion 20 between the two oil seals 15 and 16 provided on the outer peripheral surface to the hydraulic oil chamber 18. Thus, a check valve 22 having a relief function is interposed. Reference numeral 23 denotes a supply / discharge port for moving hydraulic oil into and out of the hydraulic oil chamber 18.

Thus, when the internal drain type lift cylinder 1 configured as described above is used as a lift cylinder of, for example, a forklift which is an industrial vehicle, pressure hydraulic oil is sent from the supply / discharge port 23 to the hydraulic oil chamber 18. Then, the piston 5 is pushed to extend the inside of the cylinder tube 4 with the piston rod 6.

Further, with this, the gas in the gas chamber 19 compressed at that time pushes out the lip from the back side of the dust seal 17 and is released to the atmosphere, and the lift arm of the forklift or the lift arm and the lift arm are placed on the lift arm. Up along the mast with the loaded luggage.

On the other hand, contrary to the above,
3 is switched to the communication with the oil storage tank, the piston 5 is pushed by the total load of the lift arm, the piston 5 and the piston rod 6 due to their own weights, or a load obtained by adding the weight of the load to the lift arm. The hydraulic oil in the oil chamber 18 is compressed with the piston rod 6 while being pushed out from the supply / discharge port 23 to the oil storage tank.

At this time, the gas chamber 19 is expanded to a negative pressure, and the negative pressure impedes the above-described compression operation. However, the lift arm and the piston 5 and the piston rod 6 are opposed to the negative pressure. By setting so that the compression operation can be performed with the total load of each own weight, the lift arm or the lift arm and the load loaded thereon are lowered together along the mast.

If the supply / discharge port 23 is closed in any of the extending and compressing operations, the piston 5 is locked while maintaining the state at that time, and the lift arm or the lift arm and the lift arm are placed thereon. Hold the load at that level.

Further, it is assumed that the pressure hydraulic oil in the hydraulic oil chamber 18 leaks from the lower oil seal 15 provided on the piston 5 and accumulates in the portion 20 between the hydraulic oil chamber 18 and the upper oil seal 16 during the above-described expansion and contraction operation. Also, when the accumulated pressure of the leaked oil exceeds the sum of the operating oil pressure of the operating oil chamber 18 and the set pressure of the check valve 22 having a relief function, the return oil passage 21 formed in the piston 5 causes the oil to leak from the return oil passage 21. The check valve 22 is pushed open and released directly to the hydraulic oil chamber 18 side.

As a result, in the embodiment of FIG. 1, there is no need to form a hollow reservoir chamber for the piston rod 6 as in the prior art, so that the number of processing steps and cost can be reduced. In addition to this, the strength of the piston rod 6 can also be improved.

On the other hand, an internal drain type lift cylinder 1a according to another embodiment of the present invention shown in FIG.
The return oil passage 21 for the piston 5 and the check valve 22 having a relief function in the internal drain type lift cylinder 1 according to the embodiment are omitted, and instead, the oil seal 15 below the piston 5 The check valve 22 is configured to also have a function.

That is, in this case, the two oil seals 15 provided on the piston 5 from the hydraulic oil chamber 18,
In order to return the leaked oil to the working oil chamber 18 when the working oil leaking to the portion between the two reaches a predetermined accumulated pressure, the working oil chamber 18 of these two oil seals 15 and 16 is used. The oil seal 15 located on the side is interposed in the direction in which the lip opens due to the accumulated pressure from the back side.

Thus, when the internal drain type lift cylinder 1a expands and contracts, the pressure hydraulic oil in the hydraulic oil chamber 18 leaks from the lower oil seal 15 provided on the piston 5 and moves between the upper oil seal 16 and the hydraulic oil. Even if the oil accumulates in the portion 20, when the accumulated pressure of the leaked oil becomes higher than the hydraulic oil pressure in the hydraulic oil chamber 18, the lip of the oil seal 15 is pushed open from the back side to the hydraulic oil chamber 18 side. Is released.

From the above, in the embodiment of FIG. 2, it is not necessary to perform special processing not only on the piston rod 6 but also on the piston 5, so that the piston 5 and the piston rod 6 are not required to be processed. The strength can be improved, and the number of processing steps and cost can be further reduced.

[0031]

As described above, according to the first aspect of the present invention, the portion between the two oil seals provided on the outer peripheral surface of the piston is returned to the hydraulic oil chamber by the return oil passage provided in the piston. By providing a check valve having a relief function to this return oil passage, the hydraulic oil leaking from the hydraulic oil chamber to the portion between these two oil seals reaches a predetermined accumulated pressure. When this is done, the leaked oil can be returned to the hydraulic oil chamber side while pushing open the check valve having the relief function from the portion between the two oil seals and directly through the return oil passage provided in the piston, thereby opening the check valve.
Since it is not necessary to provide a special configuration for the piston rod, it is possible to reduce the number of processing steps and cost, and also to improve the strength of the piston rod.

According to the second aspect of the present invention, instead of providing the piston with a check valve having a return oil passage and a relief function as in the first aspect of the present invention, the piston is provided. The piston is configured such that the oil seal located on the hydraulic oil chamber side of the two oil seals provided on the outer peripheral surface is interposed in the direction in which the lip opens due to the accumulated pressure of oil leaking from the rear side. Since it is not necessary to apply a special configuration not only to the rod but also to the piston, the strength of the piston rod can be improved while further reducing the number of processing steps and the cost.

[Brief description of the drawings]

FIG. 1 is a partial vertical sectional front view showing an embodiment of an internal drain type lift cylinder according to the present invention.

FIG. 2 is a partial vertical sectional front view showing another embodiment of the internal drain type lift cylinder according to the present invention.

[Explanation of symbols]

 1, 1a Internal drain type lift cylinder 2 Cylinder bottom 3 Cylinder head 4 Cylinder tube 5 Piston 6 Piston rod 15 Oil seal on hydraulic oil chamber side 16 Another oil seal 17 Dust seal 18 Hydraulic oil chamber 19 Gas chamber 20 Two oil seals Between the parts 21 Return oil passage 22 Check valve with relief function 23 Supply / discharge port

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tatsu Kawai 2-4-1 Hamamatsucho, Minato-ku, Tokyo World Trade Center Building Kayaba Industry Co., Ltd. F-term (reference) 3H081 AA03 BB02 CC20 DD02 HH03

Claims (2)

[Claims] 1. Two oil seals are disposed at intervals on a sliding surface of a piston with respect to a cylinder, and the interior of the cylinder is separated by a piston into a lower hydraulic oil chamber and an upper gas chamber via the oil seals. In the partitioned lift cylinder, these two oils are used to return the leaked oil to the hydraulic oil chamber when the hydraulic oil leaking from the hydraulic oil chamber to the portion between the oil seals reaches a predetermined pressure. An internal drain type lift cylinder, wherein a portion between seals communicates with a hydraulic oil chamber through a return oil passage provided in a piston, and a check valve having a relief function is interposed in the return oil passage. 2. Two oil seals are arranged at intervals on the sliding surface of the piston with respect to the cylinder, and the interior of the cylinder is divided into a lower working oil chamber and an upper gas chamber by the piston via these oil seals. In the partitioned lift cylinder, two oil seals are used to return the leaked oil to the hydraulic oil chamber side when the hydraulic oil leaking from the hydraulic oil chamber to a portion between the oil seals reaches a predetermined accumulated pressure. An internal drain type lift cylinder, wherein an oil seal located on the side of the hydraulic oil chamber is interposed in a direction in which the lip is opened by the accumulated pressure from the back side.