JPH05248411A - Cylinder device - Google Patents

Abstract

PURPOSE:To provide a cylinder which can prevent leakage of oil by regulating the inclination of a piston, and holding down the bending of a piston rod due to the action of bending load to be smaller. CONSTITUTION:A cylinder device comprises a cylinder tube 3, a piston 7 adapted to slide in the cylinder tube 3, at least two or more bearings 8, 9 provided on the outer periphery of the piston 7 inside both axial ends of the piston 7, and a piston rod 5 associated with the piston 7. The bearings 8,9 are provided on both ends of the piston 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to reducing the bending of a piston rod due to a load in a cylinder device which is optimal for expanding and contracting a boom of a crane, for example.

[0002]

2. Description of the Related Art FIGS. 3 to 5 show a cylinder 1 which is most suitable for sliding and extending a boom of a crane. The crane boom slides telescopically and is stored in multiple stages. That is, the second boom 2 is provided inside the first boom 6, and the cylinder 1 is provided inside the second boom 2. The cylinder 1 fixes the flange portion 4 of the cylinder tube 3 and the rear end portion of the second boom 2. The end of the piston rod 5 is fixed to the first boom 6 side. Since the cylinder tube 3 and the second boom 2 are fixed and the piston rod 5 and the first boom 6 are fixed in this way, when the cylinder 1 expands and contracts, the second boom 2 and the cylinder tube 3 move together. Move to.

In the cylinder 1, a gap is provided between the piston 7 and the cylinder tube 3, and bearings 8 and 9 are fitted around the piston. These bearings 8 and 9 are
As shown in FIG. 4, they are provided inside by L ₂ from both axial ends of the piston 7. Therefore, the distance L ₁ at which the bearings 8 and 9 support the piston 7 is shorter than the axial length L of the piston 7 by 2L ₂ . Therefore, the piston 7 is unstable with respect to the tilt by L ₂ . Reference numerals 10 and 11 are an oil seal and a backup seal.

Further, since the second boom 2 is housed in multiple stages in a telescopic manner, its internal space is narrow. The cylinder 1 to be housed in this narrow internal space is inevitably thin. In the cylinder 1 having a small diameter, the cylinder tube 3 is also thin. If the cylinder tube 3 is thin, the piston rod 3 must be thin.
If the piston rod 3 is thin, the piston rod 3 is easily bent, and the bending strength is reduced. As described above, in the cylinder 1 having a small diameter, the bending strength of the piston rod 5 becomes a problem.

Particularly when the cylinder 1 is in the most contracted state, the piston 7 moves to the bottom side 13 as much as possible, so that the distance between the flange portion 4 of the cylinder tube 3 supporting the piston rod 5 and the piston 7 is long. Become. In this state, the piston rod 5 having a low bending strength may be bent by its own weight. Further, the piston 7 linked with the piston rod 5 having a low bending strength is easily tilted. Therefore, when the piston rod 5 bends due to its own weight, a force acts in a direction to tilt the piston 7, and the piston 7 tilts as the piston rod 5 flexes. In this way, when the piston 7 is tilted, the piston rod 5 is further bent by the tilted amount.

[0006] When hoisting a load with a crane, if the boom is extended and the load is hung, the moment increases due to the length of the boom, so the crane itself becomes unstable and there is a risk of tipping over. May be bent. Therefore, when the boom is extended, the allowable load limit is set low. If the allowable limit of the suspended load is set low, the load acting in the direction of compressing the cylinder 1 in the boom is small. Therefore, even if the bending strength of the piston rod 5 is low, the piston rod 5 will not be bent. However, if the boom is in the most contracted state and the load is suspended, the piston rod 5 bends. That is, when the load is raised and lowered with the boom being in the most contracted state, the crane itself is stable and there is no risk of tipping because the moment is small because the boom is short. Also, because the moment is small, the boom does not bend. Therefore, the allowable limit of the suspended load can be set high. If the allowable limit is set high, the load acting in the direction of compressing the cylinder 1 becomes large. Therefore, there is a problem that the piston rod 5 having a low bending strength is bent.

When the boom is in the most contracted state, the cylinder 1 is also in the most contracted state. In the cylinder 1 in this state, as described above, the piston rod 5 may bend due to its own weight. In addition, the piston 7
Is easily tilted, the flexure of the piston rod 5 becomes large.

[0008]

As described above, in the conventional cylinder 1, the bending strength of the piston rod 5 is low and the structure in which the piston 7 is easily inclined allows the boom to be allowed in the most contracted state. When a heavy load close to the limit is lifted, there is a problem that the piston rod 5 bends greatly. That is, the piston rod 5
Since the bending strength is low, the piston rod 5 may be bent by its own weight. Further, when the piston rod 5 bends, the piston 7 tilts following the bending of the piston rod 5, and the piston rod 5 bends more. When a heavy load close to the allowable limit acts on the cylinder 1 in this state, this load acts in a direction of contracting the cylinder 1. Then, this load acts on the piston 7 and the piston rod 5, but since the piston 7 is inclined, it acts on the piston rod 5 in the direction of arrow b in FIG.
Therefore, the piston rod 5, which is bent by its own weight, further receives a force in the direction of arrow b. As a result, there is a problem that the piston rod 5 is largely bent.

When the piston rod 5 is largely bent in this way, when the piston rod 5 moves inside the cylinder tube 3, a seal portion (not shown) on the flange portion 4 of the cylinder tube 3 is pressed against the piston rod 5. Will be damaged. For this reason, oil leaks from the seal portion of the cylinder tube 3. Also,
If the piston rod 5 is bent more severely, the piston rod 5 and the cylinder tube 3 may come into contact with each other, and the piston rod 5 and the cylinder tube 3 may be damaged. When the damaged piston rod 5 moves, oil leaks from the scratch of the piston rod 5, and the seal portion of the cylinder tube 3 is damaged by the scratch of the piston rod 5, causing oil leakage. An object of the present invention is to control the inclination of the piston 7 and suppress the bending of the piston rod 5 to a small value.
It is to provide a cylinder that prevents oil leakage.

[0010]

In order to solve the above-mentioned problems, according to the present invention, a cylinder tube, a piston that slides in the cylinder tube, and an outer circumference of the piston, which is located at both ends in the axial direction of the piston In a cylinder device including at least two bearings provided inside and a piston rod linked to the piston, the bearings are provided at both ends of the piston.

[0011]

Since the bearings are provided at both ends of the piston, the stability with respect to the inclination of the piston is improved, and the piston is less likely to be inclined. Since the piston is hard to tilt, for example, in lifting work of a crane, when the boom is in the most contracted state and a heavy load near the allowable limit is lifted, the piston can be prevented from being largely bent by the piston.

[0012]

1 and 2 show an embodiment of the present invention. The same components as those of the conventional example described above are denoted by the same reference numerals, and detailed description thereof will be omitted. Here, ring-shaped bearings 8 and 9 are provided at both ends of the piston 7. That is, by providing the bearings 8 and 9 at both ends of the piston 7, the axial length L of the piston 7 and the distance L ₁ between the ends of the bearings 8 and 9 are made equal. In this way, the distance for supporting the piston 7 by the bearings 8 and 9 is lengthened to improve the stability of the piston 7 against tilting and make the piston 7 hard to tilt. Also, since the piston 7 is difficult to tilt,
When the cylinder 1 is in the most contracted state, the bending of the piston rod 5 due to its own weight can be suppressed to be small.

When the boom is contracted to lift a heavy load close to the allowable limit, a large load acts in the direction of contracting the cylinder 1. At this time, the cylinder 1 is in the most contracted state, but since the piston 7 is not easily tilted as described above, the bending of the piston rod 5 due to its own weight is suppressed to a small level. In addition, since the piston 7 is difficult to tilt, the piston 7 will not move due to the suspended load.
The direction of the force exerted on the cylinder tube 3 is the axial direction of the cylinder tube 3 as indicated by the arrow a in FIG. Therefore, the force does not act in the direction of increasing the bending of the piston rod 5 as shown by the arrow b in FIG. 5 of the conventional example. As described above, since the piston 7 is less likely to tilt, the bending of the piston rod 5 due to its own weight is suppressed to a small level, and in addition, the direction of the force exerted by the piston 7 on the piston rod 5 due to the suspended load is determined by the cylinder tube. Coupled with the fact that it works in the axial direction of 3, the piston rod 5 does not bend greatly.

In this way, by making the piston 7 hard to tilt,
Since the piston rod 5 is not bent so much,
The movement of the piston rod 5 pressed the seal portion of the cylinder tube 3 and prevented damage. Therefore, oil does not leak from the seal portion of the cylinder tube 3. Moreover, the piston rod 5 was not bent so much that the piston rod 5 and the cylinder tube 3 were in contact with each other, and the piston rod 5 and the cylinder tube 3 were not damaged. Therefore, the piston rod 5
Is moved, the seal portion of the cylinder tube 3 is damaged, oil leakage does not occur there, and oil does not leak from the scratch of the piston rod 5.

[0015]

[Effect] Since the bearings are provided at both ends of the piston in the axial direction to prevent the piston from tilting, the force in the bending direction of the piston rod can be suppressed by the piston, and a large bending of the piston rod can be suppressed. Therefore, for example, in the crane lifting work, make the boom the most contracted state,
When lifting a heavy load near the allowable limit, the piston rod does not bend significantly even if a heavy load acts on the piston rod. Since the piston rod does not bend greatly, the piston and cylinder tube make contact,
Both are not hurt. Since the piston rod is not scratched, oil leaks from the scratch and oil leakage due to scratching the cylinder tube seal due to movement of the piston rod is eliminated. Further, since the piston is made hard to tilt, it is possible to suppress the bending of the piston rod due to its own weight, and the piston rod becomes more difficult to bend.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

FIG. 2 is a schematic view showing bending of a piston rod when a load is applied in the embodiment.

FIG. 3 is a schematic view of a boom of a crane and a cylinder provided inside the boom.

FIG. 4 is an enlarged schematic view of a portion of a cylinder.

FIG. 5 is a schematic view showing bending of a piston rod when a load is applied in a conventional example.

[Explanation of symbols]

 1 Cylinder 3 Cylinder Tube 5 Piston Rod 7 Piston 8 Bearing 9 Bearing

Claims (1)

[Claims] 1. A cylinder tube, a piston that slides in the cylinder tube, at least two bearings provided on the outer circumference of the piston on the inner side of both axial ends of the piston, and linked to the piston. A cylinder device including a piston rod, wherein the bearing is provided at both ends of the piston.