JPH085637B2 - Lift cylinder cushion mechanism - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lift cylinder mainly used as a hydraulic actuator of a lifting device for an industrial vehicle such as a forklift, and more specifically, stops at a stroke end, particularly at a rising end. The present invention relates to a cushion mechanism for cushioning a shock at the time.

(Prior Art) Various cushion mechanisms have been conventionally known for cushioning the shock generated at the stroke end of a lift cylinder, and examples thereof include Japanese Utility Model Laid-Open No. 56-124699 and Japanese Utility Model Publication No. 56-124699. Kakai 56-45606 and the like can be mentioned. However, the cushion mechanisms disclosed in the above publications both relate to the descending end.

That is, a conventional lift cylinder of a forklift usually has a cushion mechanism at the lower end but does not have a cushion mechanism at the upper end. This is due to the fact that the ascending speed of the cylinder was not so high, but in recent years, the ascending speed has been increased for the purpose of improving the efficiency of cargo handling work. It is requested to install a cushion mechanism.

As a proposal to meet such a demand, for example, Japanese Utility Model Laid-Open No. 60-28791 can be cited. This is because when the bottom side oil chamber and the rod side oil chamber are connected by the oil passage provided in the piston of the lift cylinder and the hydraulic oil of the hydraulic pump is supplied to the bottom side oil chamber to raise the piston, A so-called differential lift cylinder that allows the hydraulic oil in the chamber to flow into the bottom side,
When the piston approaches the ascending end, the rod-side opening of the oil passage is closed, and then the working oil in the rod-side oil chamber is caused to flow through the small-diameter passage provided in the piston to the bottom-side oil chamber. The speed is reduced to absorb the shock generated at the rising end.

(Problems to be Solved by the Invention) However, the lift cylinder disclosed in Japanese Utility Model Laid-Open No. Sho 60-28791 described above raises due to the difference in pressure receiving area between the bottom side oil chamber and the rod side oil chamber, a so-called ram type. Since it is a differential type cylinder, it is necessary to set the cylinder diameter large in order to obtain a large thrust. In the case of a forklift, the increase in the diameter of the lift cylinder means that the entire loading device including the mast is arranged so as to be displaced forward by an amount corresponding to the increase in the cylinder diameter. However, there is a problem in that the allowable load is reduced due to the fact that it becomes a front side.

Therefore, in view of the above-mentioned problems, the present invention provides a cushion mechanism for a lift cylinder that can effectively cushion the impact at the rising end and that does not have the problem of increasing the lift cylinder diameter. To aim.

(Means for Solving the Problems) In order to solve the above problems, the present invention is configured as follows.

That is, a piston fitted to the inner circumference of the cylinder tube with a predetermined clearance, a wear ring fitted to the outer circumference of the piston and slidably tightly fitted to the inner circumference surface of the cylinder tube, and the cylinder tube. In a lift cylinder having a main oil port provided at an upper end portion of the rod side oil chamber and an oil tank communicating with each other through a pipe, the wear ring is provided from a vicinity of a rising end in a working area of the piston to a rising end. Is formed so as to be able to close the main oil port over a range of up to, and a slit that connects the rod side oil chamber and the bottom side oil chamber is provided at an arbitrary position on the outer circumference, and the main oil port of the cylinder tube is also provided. A sub oil port that is always kept open is provided above the The connecting path connecting the port and the port is provided with a check valve that allows the hydraulic oil to flow into the rod-side oil chamber side and prevents the reverse flow.

(Operation) According to the cushion mechanism according to the present invention configured as described above, during the ascending operation in which the hydraulic oil from the oil pump is supplied to the bottom side oil chamber, the wear ring of the piston moves to the rod side oil chamber. Until the main oil port is closed, the hydraulic oil in the rod-side oil chamber is returned to the oil tank through the main oil port, and during this time, a thrust commensurate with the cross-sectional area of the bottom-side oil chamber is obtained.

Further, when the piston moves up to approach the rising end and the wear ring closes the main oil port, the working oil in the rod side oil chamber then flows out to the bottom side oil chamber through the slit in the wear ring. Therefore, the pressure in the rod-side oil chamber becomes high, and the rod-side oil chamber acts as a cushion chamber to reduce the rising speed of the piston.

When the piston that returns the hydraulic oil from the bottom side oil chamber to the oil tank descends, the hydraulic oil in the oil tank pushes the check valve and opens through the communication passage to the sub oil port until the wear ring opens the main oil port. To the rod-side oil chamber, the piston starts to descend smoothly without a time lag, and after the wear ring opens the main oil port, the hydraulic oil flows in from the main oil port.

(Example) Hereinafter, the Example of this invention is concretely described based on drawing.

As shown, the lift cylinder is a cylinder tube 1
A bottom cover 2 fixed to the lower end of the tube, a top cover 3 fitted to the upper end of the tube, a piston 4 fitted in the tube, and a piston rod concentric with the piston 4. 5, and the inside of the cylinder tube 1 is partitioned by a piston 4 into a bottom side oil chamber 1A and a rod side oil chamber 1B.

Generally, a gap of about 0.5 to 1.0 mm is set between the inner peripheral surface of the cylinder tube 1 and the outer peripheral surface of the piston 4 in order to avoid damage due to direct contact between the metals. This gap causes wobbling of the piston 4, and in order to prevent it, a wear ring 6 that is fitted in close contact with the inner peripheral surface of the cylinder tube 1 is fitted to the outer periphery of the piston 4. At the same time, a bush 7 which is closely fitted to the outer circumference of the piston rod 5 is fitted to the inner circumference of the upper end of the cylinder tube 1 via a rod guide 8.

In general, the bush 7 is made of iron and has a resin coated surface, and the wear ring 6 is made of cloth-containing phenol resin. In the case of the present embodiment, two wear rings 6 are fitted to the piston 4 in two upper and lower stages, and each of the wear rings 6 extends in an inclined direction in the axial direction (vertical direction). For example, a slit 6a having a width of 1 mm is provided as a hydraulic oil passage.

A U-packing 9 is fitted to the lower part of the outer periphery of the piston 4 with its groove facing downward.
Can almost completely prevent the oil leakage from the bottom side oil chamber 1A to the rod side oil chamber 1B, but when the rod side oil chamber 1B is at a high pressure, the working oil causes the lip to bend to the inner peripheral side. However, it is usually possible to flow to the bottom side oil chamber 1A side.

On the other hand, a main oil port 10 is provided above the cylinder tube 1, and a sub oil port 11 is provided above the main oil port 10, so that the main oil port 10 rises in the operating region of the piston 4. The wear ring 6 closes the sub oil port 11 in the range from the end to the rising end, but the sub oil port 11 is always open. And, on the outer surface of the upper part of the cylinder tube 1,
A main oil passage 12 communicating with the main oil port 10,
A boss 14 having a sub oil passage 13 communicating with the sub oil port 11 is fixed, and the main oil passage 12 is fitted.
It is connected to an oil tank (not shown) via a high-pressure pipe attached to 15. Further, the main oil passage 12 and the sub oil passage 13 communicate with each other through a communication passage 16,
A check valve 17 that allows the flow from the main oil passage 12 side to the sub oil passage 13 and blocks the reverse flow is inserted in the valve 16. In addition, 18 is a stopper.

The lift cylinder provided with the cushion mechanism for the rising end of the present embodiment is an oil-filled type in which not only the bottom side oil chamber 1A as described above, but also the rod side oil chamber 1B is filled with hydraulic oil, It works as follows.

When the hydraulic oil from the hydraulic pump is supplied to the bottom side oil chamber 1A, the piston 4 is lifted up, and until the wear ring 6 on the upper side closes the main oil port 10, the hydraulic oil in the rod side oil chamber 1B is Main oil port 10 to main oil passage
After 12 it is returned to the oil tank. Therefore, during this time, a thrust force commensurate with the cross-sectional area of the bottom side oil chamber 1A is obtained. Then, when the piston 4 approaches the vicinity of the rising end and the main oil port 10 is closed by the upper wear ring 6, the rod-side oil chamber 1B thereafter starts to function as a cushion chamber.

That is, as shown in FIG. 2, the main oil port 10
When the outflow of the hydraulic oil from the oil is blocked, the hydraulic oil in the rod side oil chamber 1B flows out to the bottom side oil chamber 1A as shown by the arrow in the figure, but in this case, as described above, the outer peripheral surface of the piston 4 is There is a gap between the cylinder tube 1 and the inner peripheral surface of the cylinder tube 1, and the U packing 9 allows the flow from the rod side oil chamber 1B to the bottom side oil chamber 1A side, so that the working oil eventually becomes the upper and lower wear rings. The oil is discharged to the bottom side oil chamber 1A in a flow regulated by the slit 6a of No. 6. Therefore, the pressure in the rod side oil chamber 1B increases, and the rising speed of the piston 4 decreases.

The cushioning action for speed regulation is performed until the piston 4 shown in FIG. 3 comes into contact with the rod guide 8 in the ascending end state, thereby cushioning the impact when the ascending end is reached. With a forklift, it is possible to prevent the cargo from collapsing and falling, thus ensuring work safety.

During the cushion action, the hydraulic oil does not escape from the sub oil port system having the check valve 17.

On the other hand, when the piston 4 is lowered by causing the hydraulic oil in the bottom side oil chamber 1A to flow out to the oil tank, the hydraulic oil from the oil tank will not be discharged when the main oil port 10 is blocked by the wear ring 6. It flows through the oil passage 12, the communication passage 16, the check valve 17, the sub oil passage 13, and the sub oil port 11 into the rod side oil chamber 1B, starts descending without a time lag, and the wear ring 6 passes. After the main oil port 10 is opened, the hydraulic oil flows in through the main oil port 10.

By the way, in this embodiment, since the wear ring 6 has two upper and lower stages, when the land width which is the outer circumference of the piston between the wear rings 6 is formed wider than that shown in the drawing during the cushioning operation described above, When the land portion corresponds to the main oil port 10, a part of the hydraulic oil that has passed through the slit 6a of the upper wear ring 6 wraps around to the land portion and comes out from the main oil port 10 to the oil tank side. , As a result, the effectiveness of the cushion changes. That is, the cushion performance can be appropriately adjusted by setting the land width between the upper and lower wear rings 6.

Further, the wear rings 6 are provided in the upper and lower stages, so that the U packing 9 is damaged by the back pressure, that is, the high pressure oil concentrates on a part of the lip of the U packing 9, and the lip is formed by the piston 4 and the cylinder. It is possible to prevent the phenomenon that the U-packing 9 protrudes into the gap with the tube 1 and is damaged, which is also effective in protecting the U packing 9.

In addition, the cushioning performance for restricting the rising speed of the piston 4 as described above has the slit of the wear ring 6.
Since it is determined by the flow rate of the hydraulic oil flowing through 6a, if several wear rings 6 having different widths of the slits 6a are prepared in advance and an appropriate one is selected from them, it is It is possible to easily provide a lift cylinder having a cushioning property that can meet the demand.

Furthermore, the wear ring 6 is adjusted so that the slit 6a does not pass over the main oil port 10 when it is assembled, that is, does not communicate. However, the wear ring 6 is actually used while the lift cylinder is in use.
May move around the piston 4 and the slit 6a may communicate with the main oil port 10 as shown in FIG. When communicating, the hydraulic oil in the rod-side oil chamber 1B may flow out from the main oil port 10 to the oil tank, and the effectiveness of the cushioning action may be impaired. It can be reduced by changing as shown in (b) to (e) of the figure.

FIG. 4B shows the slit 6a formed in two steps, FIG. 4C shows the slit 6a having a large inclination angle, and FIG. 4D shows the slit 6a formed in a stepwise manner. In addition, (e) is the wear ring 6 subdivided into upper and lower parts, and in any of the examples, the cushioning effect is reduced by shortening the communication continuation time when the slit 6a and the main oil port 10 communicate with each other. It is possible to decrease.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to effectively buffer the shock generated when the lift cylinder reaches the rising end, and when applied to the lift cylinder of a forklift. In this case, it is possible to prevent the load from collapsing or falling and to ensure work safety. In addition, since there is no need to worry about a collapsing load, it is possible to increase the piston rising speed. It will be possible and will help to improve the efficiency of cargo handling work.

Moreover, the cushion mechanism of the present invention is an oil-filled lift cylinder and is applied to a cylinder that returns the working oil in the rod-side oil chamber to the oil tank. It is possible to avoid the problem of reducing the allowable load and avoid the problem of reducing the allowable load found in a ram type lift cylinder that is lifted due to the difference in the pressure receiving area, and to obtain the freedom in layout. Further, since the cushion mechanism according to the present invention has a structure in which the slit is formed in the wear ring provided to prevent the wobbling of the piston, the cushion performance can be freely obtained by adjusting the slit width.

[Brief description of drawings]

The drawings show an embodiment of the present invention. FIG. 1 is a vertical cross-sectional view of a lift cylinder equipped with a lifting end cushion mechanism, FIG. 2 is a vertical cross-sectional view showing a cushion action start state, and FIG. FIG. 4 is a vertical cross-sectional view showing a state, and FIG. 4 is an explanatory diagram relating to the shape change of the slit formed in the wear ring. 1 …… Cylinder tube, 1A …… Bottom side oil chamber 1B …… Rod side oil chamber, 4 …… Piston 6 …… Wear ring, 6a …… Slit 10 …… Main oil port 11 …… Sub oil port 12 …… Main oil passage, 13 …… Sub oil passage 16 …… Communication passage, 17 …… Check valve

Claims (1)

[Claims] 1. A piston that fits in the inner circumference of a cylinder tube with a predetermined clearance, and a wear ring that is fitted to the outer circumference of the piston and is tightly slidably fitted in the inner circumference surface of the cylinder tube. In a lift cylinder provided at an upper end portion of the cylinder tube and having a main oil port that communicates a rod-side oil chamber and an oil tank via a pipe, the wear ring is near an ascending end in a working area of a piston. To a rising end, the main oil port is formed so as to be blocked, and a slit communicating between the rod side oil chamber and the bottom side oil chamber is provided at an arbitrary position on the outer circumference, and the cylinder tube is provided with the slit. A sub oil port that is always kept open is provided above the main oil port. A cushion mechanism for the lift cylinder equipped with a check valve that allows hydraulic oil to flow into the oil chamber side of the rod and blocks the reverse flow in the communication path that connects the valve and the valve.