JP2000170711A - Hydraulic cylinder - Google Patents

Abstract

(57) [Problem] To eliminate the need to form a hollow portion corresponding to a reservoir in a piston rod, improve workability, secure the strength of the piston rod, and reduce the pressure supplied to the piston side. To provide a hydraulic cylinder. SOLUTION: A cylinder 1, a piston rod 3 movably inserted into the cylinder 1 via a piston 2, a rod-side gas chamber 4 and a non-rod-side pressure chamber partitioned through the piston 2 in the cylinder 1. 5, and a check valve mechanism 6 for opening and closing the gas chamber and the pressure chamber, wherein the internal pressure of the gas chamber 4 is set to a negative pressure state in the most compressed state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic cylinder mounted on an industrial vehicle such as a forklift and suitable for use as a lift cylinder for lifting and lowering cargo.

[0002]

2. Description of the Related Art As this type of hydraulic cylinder, for example,
The one disclosed in Japanese Patent Application Laid-Open No. 10-122205 has been developed.

This hydraulic cylinder includes a cylinder, a piston rod movably inserted into the cylinder via a piston, a rod-side oil chamber and a non-rod-side oil chamber defined inside the cylinder via a piston, and a piston. It is provided with a hollow portion as a reservoir formed in the rod and communicating with the rod-side oil chamber, and a relief valve provided between the reservoir and the non-rod-side oil chamber so as to be openable and closable.

When the above-mentioned conventional hydraulic cylinder is mounted on a vehicle such as a forklift as a lift cylinder, the load is lifted and lowered via the lift cylinder. Then, when the piston rod is extended by supplying pressure oil to the non-rod side oil chamber and the load is raised, the reservoir compensates for the amount of oil that the piston rod retreats due to the decrease in the volume of the rod side oil chamber. Similarly, the pressure increase in the rod-side oil chamber is suppressed by the hollow portion, and the extension operation of the piston rod is smoothly performed.

[0005]

Although the above-mentioned hydraulic cylinder is not particularly defective in function, it has a hollow portion in the piston rod in order to suppress an increase in pressure in the rod-side oil chamber. The number of man-hours increases and causes an increase in cost. In addition, since the hollow portion is formed in the piston rod, the cross-sectional area of the rod is reduced, which is disadvantageous in strength.

Accordingly, an object of the present invention is to provide a hydraulic cylinder which does not need to form a hollow portion in a piston rod, improves workability, can secure the strength of the piston rod, and requires only a small pressure to be supplied to the piston side. It is to provide.

[0007]

In order to achieve the above object, the present invention comprises a cylinder, a piston rod movably inserted into the cylinder through a piston, and a partition in the cylinder through the piston. And a check valve mechanism that opens and closes the gas chamber and the pressure chamber. The internal pressure of the gas chamber is set to a negative pressure state at the most compressed state. It is characterized by becoming.

In this case, a passage connecting the gas chamber and the pressure chamber is formed between the piston or the piston and the piston rod, and a check comprising a valve body and a spring for urging the valve body in the closing direction is formed in the passage. A valve mechanism is provided so as to be openable and closable, and the pressure in the gas chamber is released to the pressure chamber via the check valve mechanism at the time of extension operation, so that the internal pressure of the gas chamber becomes a negative pressure state in the most compressed state. Is preferred.

Similarly, a check valve mechanism is constituted by a seal provided on the outer periphery of the piston and an oil passage provided on the piston so as to face the seal. Alternatively, the internal pressure of the gas chamber may be set to a negative pressure state in the most compressed state by opening to the pressure chamber.

Further, a through hole communicating the gas chamber with the atmosphere may be provided on the cylinder side, and a plug member for opening and closing the through hole may be detachably attached to the through hole.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a hydraulic cylinder according to an embodiment of the present invention, which comprises a cylinder 1, a piston rod 3 movably inserted into the cylinder 1 via a piston 2, and a cylinder 1 inside the cylinder 1. A rod-side gas chamber 4 and a non-rod-side pressure chamber 5 partitioned by a piston 2
And a check valve mechanism 6 for opening and closing the pressure chamber 5. The internal pressure of the gas chamber 4 is set to a negative pressure state in the most compressed state.

In this case, passages 7 and 8 for connecting the gas chamber 4 and the pressure chamber 5 are formed in the piston 2 or the piston 2 and the piston rod 3, and the valve body 9 and the valve body are formed in the passages 7 and 8. A check valve mechanism 6 comprising a spring 10 for urging the valve 9 in the closing direction is provided to be openable and closable by releasing the pressure of the gas chamber 4 to the pressure chamber 5 via the check valve mechanism 6 during the extension operation. In this state, the internal pressure of the gas chamber 4 is set to a negative pressure state. The details will be described below.

A bottom 11 is provided at a lower end of the cylinder 1, and a cylinder head 12 is provided at an upper part of the cylinder 1.

A recess 3 formed in the lower part of the piston rod 3
The upper end small-diameter portion 2a of the piston 1 is fitted into a, and a screw 13 is screwed into an annular groove 2b formed in the small-diameter portion 2a from the outer periphery of the piston rod 3.

The piston 2 slides up and down on the inner circumference of the cylinder 1 via a bearing 14 and an oil seal 15 provided on the outer circumference. Similarly, the outer periphery of the piston rod 3 is attached to the dust seal 1 provided on the inner periphery of the cylinder head 12.
6 and an oil seal 17 and a bearing 18 so as to freely move up and down.

A lateral passage 7 and a longitudinal passage 8 are formed in the piston 2, and a valve case 19 is inserted into the passage 8, and the valve case 19 is held by a snap ring.

In the valve case 19, a vertical passage 8a opening to the passage 8 is formed. In the middle of the passage 8a, a poppet-type valve body 9 and the valve body 9 are attached to the seat of the passage 8a. A pressing spring 10 is provided, and the spring 10 is fixed to the valve case 19 via a snap ring and a seat.

The piston side pressure chamber 5 is connected to a hydraulic pressure source via a pressure port 20 formed in the bottom 11.

When the hydraulic cylinder is assembled as a lift cylinder of an industrial vehicle such as a forklift, for example, and the hydraulic oil is supplied from the pressure port 20 and the extension operation is performed in a state in which no load is loaded, the piston 2 rises. Since the rod-side gas chamber 4 contracts, the gas pressure in the gas chamber 4 increases.

When the pressure in the gas chamber 4 reaches or exceeds the pressure in the piston side pressure chamber 5 and exceeds the set pressure of the check valve mechanism 6, the gas pressure in the gas chamber 4 opens the valve body 9 to open the pressure chamber 5 Be released to the side.

That is, when no load is loaded, the pressure in the pressure chamber 5 is low, and the pressure due to the gas compression on the gas chamber 4 side is higher than the pressure in the pressure chamber 5. Through the pressure chamber 5 side.

Next, when the pressure port 20 is connected to a low pressure side, for example, a tank in the state of reaching the maximum extension state as described above, the piston 2 is moved by its own weight such as the piston rod 3 and the machine side mast connected to the piston rod 3. Descends.

When the piston 2 descends, the gas chamber 4 is in a negative pressure state. However, since the own weight of the piston rod 3 and the mast is larger than the suction force by the negative pressure, the gas chamber 4 is contracted against the negative pressure resistance. The pressure in the gas chamber 4 can be set to a negative pressure state.

For this reason, if the pressure of the gas chamber is set to the negative pressure state in the most compressed state and then the pressure oil is supplied to the pressure chamber 5 to perform the expansion operation, the negative pressure state is eliminated with the expansion operation. ,
At this time, the pressure in the gas chamber 4 can be maintained at a value equivalent to the sum of the pressure in the pressure chamber 5 and the set pressure in the check valve mechanism 6 even when the gas reaches the maximum extension state.

Therefore, whether the load is loaded or not loaded, the pressure rise in the gas chamber 4 is small during the extension operation, so that the piston rod 3 must be provided with a hollow portion for compensating for the pressure rise. In addition, since the pressure receiving action of the gas chamber 4 acts in the direction in which the piston 2 extends in the expansion and contraction operation, the pressure supplied to the pressure chamber 5 can be small.

During use, the hydraulic oil in the pressure chamber 5 is
Even if air leaks from the cylinder head 12 or if air is sucked in from the inner periphery of the cylinder head 12, there are many opportunities to expand and contract the baggage without loading, and setting the gas chamber 4 to the initial negative pressure state as described above is extremely natural. You can do it.

FIG. 2 shows another embodiment of the present invention.

This embodiment is different from the first embodiment in that the piston 2 is replaced with a check valve mechanism comprising the valve body 9 and the spring 10 shown in FIG.
The check valve mechanism 6 is constituted by an oil seal 15 provided on the outer periphery of the piston and an oil passage 21 provided on the piston 2.

As shown in FIG. 1, an oil seal 15 having a lip facing downward is provided on the outer periphery of the piston 2, and the piston 2 has a through hole 21 facing the oil seal 15 and opening to the piston side pressure chamber 5. The oil seal 15 permits the pressure from the rod-side gas chamber 14 and the release of the leaked hydraulic oil from the outer periphery to the pressure chamber 5.

Therefore, when the baggage is extended to the maximum extension position in a non-loaded state, the pressure of the gas chamber 4 is released to the pressure chamber 5 via the check valve mechanism 6 including the oil seal 15 and the oil passage 21, and from this state. When the piston rod 3 and the piston 2 are lowered by their own weight until the maximum compression, the pressure of the gas chamber 4 can be set to a negative pressure state.

In this embodiment, since the check mechanism 6 is simple, workability and assemblability are improved, and cost can be reduced. Other structures, functions and effects are the same as those of the embodiment of FIG.

FIG. 3 relates to another embodiment of the present invention.
This is provided with a through hole 22 and a plug member 23 made of a screw or the like for opening and closing the through hole 22 in the hydraulic cylinder shown in FIG.

That is, although the hydraulic cylinders shown in FIGS. 1 and 2 have no functional problems, they are usually in the most compressed state when transported or stored in a vehicle body after an operation test, for example. In this case, since the rod-side gas chamber 4 is set in the negative pressure state, the piston 2 may be sucked and expanded by the negative pressure.

Therefore, a through hole 22 is formed in the cylinder 12, for example, in the bearing 12 as shown in the figure, to connect the gas chamber 4 and the atmosphere. The chamber 4 is communicated with the atmosphere to eliminate the negative pressure and prevent the chamber 4 from expanding.

When the hydraulic cylinder is extended in a non-loaded state to set the gas chamber 4 to a negative pressure state, the through hole 22 is opened in advance and closed in the most extended state. Can be set to a negative pressure state without releasing the pressure to the pressure chamber 5 side. Therefore, the entry of gas such as air into the pressure chamber 5 can be prevented.

On the other hand, when used in a forklift, a plug member 23 is inserted into the through hole 22 to shut off the gas chamber 4 from the atmosphere side. The inside of the chamber 4 is set to a negative pressure state.

[0038]

According to the present invention, the following effects can be obtained.

According to the invention of each claim, since the internal pressure of the gas chamber is set to the negative pressure state at least in the most compressed state, the hollow portion is formed in the piston rod in order to suppress the pressure rise in the gas chamber during the extension operation. It is not necessary to provide a work piece, so that workability and assemblability are improved, cost can be reduced, and the strength of the piston rod cannot be improved.

Similarly, when the extension operation is performed during use,
The pressure of the pressure chamber which pushes up the piston by the gas action of the gas chamber can be small, and an energy saving effect can be obtained.

According to the third aspect of the present invention, the check valve mechanism is simple, workability and assemblability are improved, and cost can be reduced.

According to the fourth aspect of the present invention, the gas chamber can be communicated with the atmosphere when it is in the most extended state, and the negative pressure is eliminated even in the low compression state during transportation and storage, so that the gas chamber is extended. Is prevented.

[Brief description of the drawings]

FIG. 1 is a partially cut-away longitudinal front view of a hydraulic cylinder according to an embodiment of the present invention.

FIG. 2 is a partially cutaway longitudinal front view of a hydraulic cylinder according to another embodiment of the present invention.

FIG. 3 is a partially enlarged longitudinal sectional front view of a hydraulic cylinder according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylinder 2 Piston 3 Piston rod 4 Gas chamber 5 Pressure chamber 6 Check valve mechanism 7, 8 Passage 9 Valve element 10 Spring 15 Seal 21 Oil passage 22 Through hole 23 Plug member

Claims (4)

[Claims] 1. A cylinder, a piston rod movably inserted into the cylinder via a piston, a rod-side gas chamber and a non-rod-side pressure chamber partitioned via a piston in the cylinder, a gas chamber and a pressure. A hydraulic cylinder, comprising: a check valve mechanism for opening and closing the chamber, wherein the internal pressure of the gas chamber is set to a negative pressure state in a most compressed state. 2. A check valve mechanism comprising: a passage connecting a gas chamber and a pressure chamber to a piston or a piston and a piston rod; and a valve body and a spring biasing the valve body in a closing direction in the passage. Is openably and closably provided so that the pressure in the gas chamber is released to the pressure chamber through the check valve mechanism at the time of extension operation so that the internal pressure of the gas chamber becomes a negative pressure state in the most compressed state. 1 hydraulic cylinder. 3. A check valve mechanism comprising a seal provided on the outer periphery of the piston and an oil passage provided on the piston opposed to the seal. 2. The hydraulic cylinder according to claim 1, wherein the internal pressure of the gas chamber is set to a negative pressure state in the most compressed state by opening the pressure chamber to the pressure chamber. 4. The hydraulic cylinder according to claim 1, wherein a through hole communicating the gas chamber with the atmosphere is provided on the cylinder side, and a plug member for opening and closing the through hole is detachably attached to the through hole.