JPH1182425A - Hydraulic cylinder buffer structure - Google Patents

Abstract

(57) An object of the present invention is to provide a buffer structure for a hydraulic cylinder that can obtain a desired relatively small cushion pressure without providing a cushion ring inserted into a head cover. SOLUTION: Rod side chamber 4b of hydraulic cylinder 1
Is mounted on the piston rod 5a, has an outer diameter substantially equal to the outer diameter of the piston 5, is disposed between the rod side chamber 4b and the piston 5, and is connected to the piston 5. An auxiliary piston 22 provided on the oil passage 7a formed between the outer peripheral surface of the auxiliary piston 22 and the inner peripheral surface of the cylinder tube 2; And a throttle member 23 that opens to the rod side chamber 4b and communicates with the oil path 7a, and is provided with a seal member 21 that can seal the oil path 7a as the auxiliary piston 22 moves toward the rod side chamber 4b. .

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 a construction machine such as a hydraulic shovel or the like, which generates a cushion pressure when the piston reaches a position near a stroke end. The present invention relates to a cushioning structure of a hydraulic cylinder provided with a cushion mechanism for preventing a shock.

[0002]

2. Description of the Related Art In construction machines such as hydraulic excavators,
Hydraulic cylinders such as boom cylinders, arm cylinders, and bucket cylinders are mounted to drive work implement members that form the front, such as booms, arms, and buckets. Since the work equipment member forming the front receives an extremely large load during the excavation work, when the hydraulic cylinder is stopped rigidly at the stroke end of the hydraulic cylinder, a large impact is applied to the work equipment member and the upper rotating body forming the main body. And so on. Therefore, a cushioning structure of a hydraulic cylinder provided with a cushion mechanism using a hydraulic pressure to absorb such an impact has been conventionally proposed.

FIGS. 4 to 8 are explanatory views showing an example of a conventional buffer structure for a hydraulic cylinder. FIG. 4 is a view showing an overview of a hydraulic cylinder provided with a conventional buffer structure, and FIG. 5 is a hydraulic diagram shown in FIG. FIG. 6 is a cross-sectional view of a main part of the hydraulic cylinder shown in FIG. 4 at the start of a cushion stroke, and FIG. 7 is a cross-sectional view of a main part of the hydraulic cylinder shown in FIG. 4 at the end of a cushion stroke. FIG. 8 is a diagram showing pressure characteristics obtained by the conventional hydraulic cylinder buffer structure shown in FIG.

In FIGS. 4 and 5, reference numeral 1 denotes a hydraulic cylinder, for example, a boom cylinder. This hydraulic cylinder 1
Has a cylinder tube 2 and this cylinder tube 2
Is closed at one end and open at the other end, and a head cover 3 is attached to the open end. The cylinder 4 is formed by the cylinder tube 2 and the head cover 3 described above.
Is configured. In the cylinder 4, a piston 5 that divides the inside of the cylinder 4 into two chambers, that is, a bottom chamber 4a and a rod chamber 4b, is slidably mounted. The piston 5 has a piston rod 5a
The piston rod 5a is connected to the head cover 3
From the outside. Further, oil paths 6 and 7 for supplying and discharging pressure oil are formed in the bottom chamber 4a and the rod chamber 4b of the cylinder 4, respectively.
The oil path 6 on the bottom side is formed at the closed end of the cylinder tube 2, and the oil path 7 on the rod side is formed on the head cover 3.

[0005] The hydraulic cylinder 1 having such a configuration
The mounting part 8 provided at the tip of the piston rod 5a is connected to the frame of the upper revolving structure provided in the hydraulic shovel, and the mounting part 9 connected to the end of the cylinder tube 2 constitutes a front member of the hydraulic shovel. When the hydraulic cylinder 1 is operated, the boom can be rotated. A cushion mechanism is provided for absorbing the impact by hydraulic action near both stroke ends when the piston rod 5a enters the cylinder 4 and contracts and when the piston rod 5a extends from the cylinder 4.

The cushion mechanism at the time of contraction is provided with a boss hole 10 as a fitting portion at the closed end of the cylinder tube 2 to open the oil passage 6 into the boss hole 10 and to open the boss hole from the end face of the piston 5. Projecting portion 1 functioning as a cushion member having an outer diameter that is inserted into small gap 10
1 is provided. As a result, the piston rod 5a enters the cylinder 4 and the piston 5 is displaced in the contracting direction, and when the piston 5 reaches the vicinity of its stroke end, the protrusion 11 comes into the boss hole 10, and at this time, Since the flow path from the bottom chamber 4a to the oil passage 6 is restricted, pressure is generated in the bottom chamber 4a,
This pressure increases in accordance with the length of the protrusion 11 inserted into the boss hole 10. This pressure becomes the cushion pressure, and decelerates the piston 5 to absorb the impact.

On the other hand, a cushion ring 12 is provided as a cushion member in the cushion mechanism on the extension side. The tip of the head cover 3 is inserted into the opening-side end of the cylinder tube 2, whereby the rod-side chamber 4 b has a stepped shape, and the portion of the head cover 3 that is inserted into the cylinder tube 2 serves as a fitting portion. .
The outer diameter of the cushion ring 12 is slightly smaller than the inner diameter of the head cover 3. The oil passage 7 is provided on the head cover 3 and opens at a position on the front side in the extending direction of the piston rod 5a from the fitting portion of the cushion ring 12. Therefore, when the piston 5 is displaced in the direction in which the piston rod 5a extends, the cushion ring 12 is attached to the head cover 3 near the stroke end thereof.
And the flow path formed by the annular gap therebetween is narrowed, and the pressure in the rod-side chamber 4b rises to generate a cushion pressure. Thus, when the cushion stroke starts and the cushion ring 12 is fitted to the head cover 3 with a predetermined fitting length, the stroke end of the hydraulic cylinder 1 is reached.

In this hydraulic cylinder 1, as shown in FIG. 5, the oil path 6 is connected to the hydraulic pump P,
Is connected to the hydraulic oil tank T, pressure oil from the hydraulic pump P is supplied to the bottom chamber 4a.
As a result, the pressure in the bottom chamber 4a increases,
By the action of this pressure, the piston 5 is slid and displaced in the cylinder 4 toward the head cover 3, and the piston rod 5 a connected to the piston 5 is extended. At this time, since the rod side chamber 4b is connected to the hydraulic oil tank T, the hydraulic oil in the rod side chamber 4b is
The oil returns to the hydraulic oil tank T from the oil path 7 through a gap between the piston rod 5a and the head cover 3.

As shown in FIG. 6, the cushion ring 12 is fitted into the head cover 3 near the stroke end in the extension direction of the hydraulic cylinder 1. As a result, the flow path from the rod-side chamber 4b to the oil path 7 becomes the flow path cross-sectional area of the diameter difference between the outer diameter of the cushion ring 12 and the inner diameter of the boss hole of the head cover 3, and the flow path from the rod-side chamber 4b is changed. The return oil flow path is restricted. As a result, the hydraulic oil tank T
The flow rate of the return oil to the chamber decreases, and a cushion pressure is generated in the rod side chamber 4b. That is, at this time, the rod-side chamber 4b forms a cushion chamber. FIG.
Is the stroke end in the extension direction of the piston rod 5a, but the cushion stroke section is a period during which the piston 5 is displaced from the form of FIG. 6 to the form of FIG. In this cushion stroke section,
As the fitting length between the cushion ring 12 and the head cover 3 increases, the throttle path of the return oil increases by that much,
As the cushion pressure in the cushion chamber increases, the hydraulic cylinder 1
Almost the entire load applied to is absorbed.

[0010] The cushion pressure according to the prior art described above varies as shown in FIG. In other words, the flow path of the return oil is an annular flow path due to the diameter difference between the outer diameter of the cushion ring 12 and the inner diameter of the boss hole of the head cover 3, and the length of the flow path changes according to the cushion stroke. , The cushion pressure increases linearly. The area of the triangle surrounded by the pressure characteristic line shown in FIG. 8 corresponds to the absorbed energy for absorbing the load applied to the hydraulic cylinder 1. Here, when a maximum load is applied to the hydraulic cylinder 1, the hydraulic cylinder 1 must be provided with a cushion characteristic capable of absorbing the load by the cushion pressure in the cushion stroke section. If the load cannot be effectively absorbed within the cushion stroke section, the piston 5 collides with the head cover 3 or the cylinder tube 2 at the stroke end, and an impact is generated. Tube 2, piston rod 5
a, the piston 5, the threaded portion connecting the piston rod 5a and the piston 5, and the head cover 3 will be damaged.

[0011]

By the way, in the cushioning structure of the hydraulic cylinder, as described above, there is a demand for securing a cushioning characteristic capable of absorbing the entire load as much as possible by the cushion pressure between the cushion strokes. This demand can be relatively easily dealt with by increasing the cushion stroke. However, in this case, the overall length of the hydraulic cylinder 1 is increased, and the construction of the construction machine is difficult.
Not realistic. Therefore, in consideration of shortening the cushion stroke and absorbing a large load, it has been conventionally performed to set the diameter difference between the cushion ring 12 and the head cover 3, that is, the annular gap to be sufficiently small (for example, The technology described in Japanese Utility Model Laid-Open No. 6-62207, etc.).

However, in the prior art shown in FIGS. 4 to 7 and the prior art shown in the above publication, FIGS.
When the cushion ring 12 is provided to be inserted into the boss hole provided in the head cover 3, the pressure receiving area of the end face of the piston 5 receiving the cushion pressure, that is, the outer diameter of the piston 5, The pressure receiving area depending on the diameter difference from the outer diameter of the cushion ring 12 tends to be small, and accordingly, the cushion pressure capable of absorbing the entire load applied to the hydraulic cylinder 1 tends to increase, and the absorbed energy more than necessary There is a problem that tends to occur.

If the cushion pressure tends to increase as described above, it becomes more difficult to set the opening amount of the small annular gap described above. Therefore, in the prior art, it is possible to generate the minimum necessary cushion pressure. It becomes difficult, and it tends to generate more cushion pressure than necessary. Therefore, the accuracy of stopping the movement of the piston 5 so as to match the stroke end, that is, the cushioning accuracy, tends to be coarse.

Further, as described above, since the cushion pressure tends to increase and the cushioning accuracy tends to be low, the prior art described above requires a cushion ring at the end of the cushion stroke when the hydraulic cylinder 1 extends. 12 and the head cover 3 are likely to collide. When such a collision occurs, the cushion ring 12 and the head cover 3 are damaged, and the hydraulic cylinder 1 is caused to fail.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned situation in the prior art, and has as its object to provide a hydraulic cylinder buffer structure capable of obtaining a desired cushion pressure without providing a cushion ring inserted into a head cover. Is to provide.

[0016]

In order to achieve the above object, according to the first aspect of the present invention, a piston having a piston rod connected thereto is slidably mounted in a cylinder so that the inside of the cylinder is slidably mounted. When the piston is displaced in a cushion stroke section of at least one of the two chambers, the flow path of the return oil from the one chamber is narrowed. In the cushioning structure of a hydraulic cylinder having a cushion mechanism for generating a cushion pressure in the one chamber and forming the one chamber in the cushion chamber, the cushion mechanism is mounted on the piston rod and has an outer diameter of the piston. An auxiliary piston having substantially the same outer diameter as that of the auxiliary piston disposed between the one chamber and the piston; It is a configuration that includes a throttle means for throttling the outlet channel of the return oil from one room above.

According to the first aspect of the present invention, when the hydraulic cylinder is extended or stopped, the auxiliary piston is one of the two chambers defined in the cylinder.
When displaced within the cushion stroke section of the chamber, the outflow channel of the return oil from the one chamber is narrowed by the throttle means, and a cushion pressure is generated in the one chamber, and the one chamber forms a cushion chamber. The generated cushion pressure is applied to the end face of the auxiliary piston, and acts on the piston via the auxiliary piston as a suppressing force for reducing the operation speed. As the piston approaches the stroke end, the cushion pressure continues to rise, and this cushion pressure absorbs almost all the load applied to the hydraulic cylinder before reaching the stroke end. Here, in the invention according to claim 1,
The cushion pressure is received at the end face of the auxiliary piston, and the outer diameter of the auxiliary piston is set substantially equal to the outer diameter of the piston. In other words, the cushion pressure is received at a relatively large pressure receiving area depending on the difference between the outer diameter of the auxiliary piston and the outer diameter of the piston rod. When absorbing the normally assumed load applied to the hydraulic cylinder in the cushion stroke section, the load to be absorbed is equivalent to the product of the cushion pressure and the pressure receiving area of the auxiliary piston. Along with the setting, a desired cushion effect can be obtained with a relatively small cushion pressure.
That is, the entire load applied to the hydraulic cylinder can be absorbed. In the invention according to claim 1,
A relatively small cushion pressure as described above can be generated without providing a cushion ring inserted into the head cover.

According to a second aspect of the present invention, in the first aspect of the present invention, the throttle means is provided with:
An oil passage which is a gap formed between an outer peripheral surface of the auxiliary piston and an inner peripheral surface of the cylinder opposed to the auxiliary piston; And a throttle hole communicating with the hole.

According to the second aspect of the present invention, the manufacturing accuracy of the auxiliary piston may be substantially equal to the manufacturing accuracy of the piston, and the process of forming a throttle hole in the auxiliary piston is simple. The opening amount of the throttle hole can be easily set to a desired value according to the diameter of the processing tool of the throttle hole.

According to a third aspect of the present invention, in the second aspect of the present invention, there is provided a sealing member capable of sealing the oil path with the movement of the auxiliary piston in the one chamber direction. It has a configuration provided.

According to the third aspect of the present invention, if the sectional area of the throttle hole is previously set smaller than the sectional area of the oil path, the oil path is sealed at the start of a cushion stroke, for example. Thus, the throttle amount of the return oil can be made to substantially depend on the opening amount of the throttle hole. Further, the force applied to the piston seal for sealing the piston can be suppressed.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the seal member has a check function for preventing inflow of pressurized oil from the one chamber to the oil passage. It is configured to include a seal member with a check.

According to the fourth aspect of the present invention, when the cushion pressure is generated, the inflow of the pressurized oil from one chamber to the oil passage is completely prevented. If the cross-sectional area of the throttle hole is set small in advance, the throttle amount of the pressure oil can be completely dependent on the opening amount of the throttle hole, and the force applied to the piston seal can be further suppressed.

[0024]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a hydraulic cylinder according to an embodiment of the present invention; FIG.
3 is an embodiment of the hydraulic cylinder buffer structure of the present invention,
For example, FIG. 1 is an explanatory view showing a buffer structure of a hydraulic cylinder provided in a hydraulic shovel, FIG. 1 is a cross-sectional view of a main part showing this embodiment, FIG. 2 is an enlarged view of a part of FIG. FIG. 2 is a diagram showing pressure characteristics obtained in the embodiment shown in FIG. In these figures, components equivalent to those shown in FIGS. 4 to 8 are denoted by the same reference numerals.

That is, reference numeral 1 shown in FIGS. 1 and 2 denotes a hydraulic cylinder, for example, a boom cylinder for driving a boom (not shown). The hydraulic cylinder 1 includes a cylinder 4 and two chambers inside the cylinder 4, that is, a bottom chamber 4a.
A piston 5 slidably formed in the cylinder 4 and divided into two chambers including a rod-side chamber 4b and a piston rod 5a connected to the piston 5 are provided.

One end of the above-mentioned cylinder tube 2 is closed, and an attachment portion 9 connected to a boom (not shown) is provided at the end. The other end of the cylinder tube 2 is open, and a head cover 3 is attached to the open end. The above-described piston rod 5a is led out from the head cover 3, and an end on the lead-out side is provided with a mounting portion 8 connected to an upper revolving unit (not shown). An oil passage 6 for supplying and discharging pressure oil and a boss hole 6 communicating with the oil passage 6 are provided on the bottom side chamber 4a.
An oil path 7 for supplying and discharging pressure oil is provided on the side of the rod-side chamber 4a.

At the end of the piston rod 5a located in the cylinder tube 2, there is provided a boss 5b which can be inserted into the boss hole 6a. These boss 5b and boss hole 6
a constitutes a cushion mechanism when return oil is discharged from the bottom chamber 4a, that is, when the bottom chamber 4a becomes a cushion chamber. The above components are the same as those shown in FIGS.

Particularly, in the present embodiment, for example, the flow path of the return oil from the rod side chamber 4b is narrowed, and a cushion pressure is generated in the rod side chamber 4b.
The cushion mechanism for forming the rod-side chamber 4b in the cushion chamber is characterized. The cushion mechanism is mounted on the piston rod 5a and has an outer diameter substantially equal to the outer diameter of the piston 5. The cushion mechanism is disposed between the rod-side chamber 4a and the piston 5, and is connected to the piston 5. The auxiliary piston 22 includes a predetermined pressure-resistant material, and a throttle means provided in the auxiliary piston 22 for restricting the flow path of the return oil from the rod-side chamber 4b.

The above-described throttle means is provided with a clearance inevitably formed between the outer peripheral surface of the auxiliary piston 22 and the cylinder 4 facing the auxiliary piston 22, ie, the inner peripheral surface of the cylinder tube 2, that is, the auxiliary piston. 2
An oil path 7a forming a gap that allows the sliding operation of No. 2;
The auxiliary piston 22 is formed at, for example, a plurality of locations, and includes a throttle hole 23 that opens to the rod-side chamber 4b and communicates with the oil passage 7a. For example, the sum of the cross-sectional areas of the throttle holes 23 is set smaller in advance than the cross-sectional area of the oil passage 7a.

Further, as the auxiliary piston 22 moves in the direction of the rod-side chamber 4b, the oil passage is moved to the portion of the cylinder tube 2 near the oil passage 7 and between the oil passage 7 and the head cover 3. 7 is provided. The seal member 21 is formed of, for example, a checked seal member having a check function of preventing the flow of pressure oil from the rod-side chamber 4b into the oil passage 7.

In FIGS. 1 and 2, reference numeral 5c denotes an outer peripheral surface of the piston 5 and an inner peripheral surface of the cylinder tube 2 so that the inside of the cylinder tube 2 is divided into the above-mentioned two chambers. 2 shows a piston seal for sealing a gap between the piston seals.

The operation of the embodiment configured as described above is as follows. When the hydraulic cylinder 1 performs an extension operation, that is, the oil passage 6 communicates with a discharge port of a pump (not shown), the oil passage 7 communicates with a tank (not shown), and hydraulic oil from the pump passes through the oil passage 6 and the boss hole 6a. When the piston 5 is supplied to the bottom chamber 4a, the hydraulic fluid supplied to the bottom chamber 4a causes the piston 5 to move leftward in FIG. At this time, the return oil of the rod side chamber 4B is returned to the tank through the oil passages 7a and 7 at the same time.

Conversely, when the hydraulic cylinder 1 performs a contracting operation, that is, the oil passage 7 communicates with a discharge port of a pump (not shown), the oil passage 6 communicates with a tank (not shown), and hydraulic oil from the pump is discharged. When the piston 5 is supplied to the rod-side chamber 4b through the oil passages 7 and 7a, the piston 5 moves rightward in FIG. 1 by the hydraulic oil supplied to the rod-side chamber 4b. At this time, the return oil of the bottom chamber 4a is simultaneously returned to the tank through the boss hole 6a and the oil path 6.

In the extension operation of the hydraulic cylinder 1 described above, in particular, in the extension operation, the piston 5 moves leftward in FIG. 1, the auxiliary piston 22 approaches the seal member 21, and the auxiliary piston 22 At the time of contact with the sealing member 21, the cushion stroke area is entered, and the cushion stroke is started. At this time, the oil passage 7a formed between the outer peripheral surface of the auxiliary piston 22 and the inner peripheral surface of the cylinder tube 2 is sealed by the seal member 21, and the return oil flows from the rod side chamber 4b to the oil passage 7a. Will be blocked. Thereby, the oil in the rod side chamber 4b is returned to the tank from the throttle hole 23 of the auxiliary piston 22 through the oil passages 7a and 7. As the piston 5 and the auxiliary piston 22 move to the left, the cushion pressure generated in the rod-side chamber 4b increases, and the pressure increases.
2, and a rightward force acts on the piston 5. As a result, the operating speed of the piston 5 is reduced, and when the stroke end is reached, the piston 5 stops, and the absorption of the shock in the extension operation of the hydraulic cylinder 1 ends.

When the hydraulic oil of the pump is supplied to the oil passage 7 while the hydraulic cylinder 1 is extended as described above, the hydraulic oil is supplied through the oil passage 7a and the throttle hole 23 to the rod side chamber 4b. To apply pressure to the auxiliary piston 5 to move the piston 5 rightward in FIG. In this case, when the boss 5b formed at the end of the piston rod 5a starts to be fitted into the boss hole 6a, the boss 5b enters the cushion region when the hydraulic cylinder 1 contracts, and the cushion pressure is applied to the bottom chamber 4a until the stroke end. Occurs
A desired cushioning effect is obtained. The cushioning effect at this time, that is, the shock absorbing effect, is the same as that of the prior art shown in FIGS.

In the embodiment configured as described above,
As described above, when the auxiliary piston 22 is displaced into the cushion stroke section of the rod-side chamber 4 a during the extension operation of the hydraulic cylinder 1, the return oil outflow channel is narrowed by the throttle hole 23, and Suppression force for reducing the speed is given to the piston 5, and the piston 5
As the stroke approaches the stroke end, the cushion pressure continues to increase, and almost the entire load applied to the hydraulic cylinder 1 is absorbed until the stroke end.

In this case, the cushion pressure is received by the end face 24 of the auxiliary piston 22, and the outer diameter of the auxiliary piston 22 is set to be substantially equal to the outer diameter of the piston 5. That is, the cushion pressure is applied to a relatively large pressure receiving area depending on the difference between the outer diameter of the auxiliary piston 5 and the outer diameter of the piston rod 5a. Hydraulic cylinder 1
In the case where the load considered in the normal work applied to the above is absorbed in the cushion stroke section, the load to be absorbed is equivalent to the product of the cushion pressure and the pressure receiving area of the auxiliary piston 22. With the setting of the area, a desired cushion action can be obtained with a relatively small cushion pressure.

The solid line in FIG. 3 shows the relationship between the stroke during the extension operation of the hydraulic cylinder 1 and the cushion pressure, that is, the pressure characteristic obtained in this embodiment.
As shown in (2), the cushion pressure at the end of the stroke can be suppressed to be smaller than the cushion pressure in the above-described conventional technology indicated by the two-dot chain line. In addition, such a relatively small cushion pressure can be generated without providing a cushion ring inserted into the head cover as in the above-described related art.

As described above, since the cushion pressure can be kept small, the force at the stroke end applied to the auxiliary piston 22 and the piston 5 with this cushion pressure is relatively small. It is relatively easy to stop the piston 5, and excellent buffering accuracy can be obtained.

Further, since the excellent cushioning accuracy is obtained as described above, the collision between the auxiliary piston 5 and the head cover 3 can be prevented, and the failure of the hydraulic cylinder 1 due to the collision can be prevented. 1 can be improved in durability.

Further, the manufacturing accuracy of the auxiliary piston 22 may be substantially the same as that of the piston 5, and the processing for forming the throttle hole 23 in the auxiliary piston 22 is simple. The desired value can be easily set in accordance with the selection of the diameter of the machining tool of the hole 23. From these, the necessary minimum cushion pressure can be relatively easily achieved, and the above-described excellent cushioning accuracy can be obtained. Contribute to securing.

As described above, at the start of the cushion stroke, the oil passage 7a is sealed by the seal member 21, so that the flow of the pressure oil from the rod side chamber 4b to the oil passage 7a is completely prevented. Since the sum of the cross-sectional areas of the throttle holes 23 is previously set smaller than the cross-sectional area of the throttle holes 7a, the throttle amount of the return oil from the rod-side chamber 4b can be made dependent on the opening amount of the throttle holes 23. By appropriately selecting the opening amount of the throttle hole 23, it is possible to ensure a higher buffering accuracy. Further, the provision of the sealing member 21 allows the rod-side chamber 4b
Can be suppressed from being applied to the piston seal 5c that seals the piston 5 through the oil passage 7, whereby the piston seal 5c can be protected. Failure of the cylinder 1 can be prevented, and durability of the hydraulic cylinder 1 can be improved.

In the above-described embodiment, the seal member 21 is constituted by a check seal member having a check mechanism for preventing the flow of pressure oil from the rod side chamber 4b into the oil passage 7a. May be replaced with a normal sealing member having no. In this case, the pressure oil in the rod-side chamber 4b slightly flows in accordance with the cushion pressure generated in the rod-side chamber 4b, but basically, the throttle amount of the return oil from the rod-side chamber 4b is substantially reduced. It can be made to depend on the opening amount of the aperture hole 23, it is possible to ensure a relatively high buffering accuracy,
Further, the force due to the cushion pressure generated in the rod side chamber 4b can be somewhat suppressed from being applied to the piston seal 5c, and the piston seal 5c can be protected.

In the above-described embodiment, the cushion mechanism constituted by the auxiliary piston 22, the throttle hole 23 and the throttle means including the oil passage 7a is provided in the rod side chamber 4b of the two chambers of the hydraulic cylinder 1. Depending on the type of work performed by the hydraulic cylinder 1, such a cushion mechanism may be provided in the bottom chamber 4a forming another chamber, or the rod side chamber 4b, It may be provided in both of the chambers 4a.

[0045]

As described above, according to the present invention, a desired cushion pressure can be obtained without providing a conventional cushion ring inserted into the head cover. Almost the entire load on the hydraulic cylinder can be absorbed by the generation of a relatively small cushion pressure via an auxiliary piston that can increase the pressure receiving area, and thus the piston must be stopped to match the stroke end. It becomes relatively easy, and it is possible to obtain excellent buffering accuracy as compared with the related art. Further, since such excellent buffering accuracy can be obtained, it is possible to prevent collision between the auxiliary piston and the head cover, prevent failure of the hydraulic cylinder due to such collision, and reduce the hydraulic cylinder Durability can be improved.

In particular, according to the invention of claim 2,
The manufacturing accuracy of the auxiliary piston is almost the same as that of the piston, and it is easy to form a throttle hole in the auxiliary piston.The opening amount of the throttle hole is determined by selecting the diameter of the processing tool for the throttle hole. Accordingly, the cushion pressure can be set to a desired value easily, and from these, the necessary minimum cushion pressure can be relatively easily achieved, which contributes to securing the above-described excellent cushioning accuracy.

According to the third and fourth aspects of the present invention, at the start of the cushion stroke, the oil path constituting the throttle means is sealed by the sealing member, and the flow of the pressure oil from the cushion chamber into the oil path is prevented. It is regulated, so that the amount of throttle of return oil from the cushion chamber can be made dependent on the amount of opening of the throttle hole, and by appropriately selecting the amount of opening of the throttle hole, it is possible to ensure a more accurate buffering accuracy. Can be. In addition, the seal member can suppress the force due to the cushion pressure generated in the cushion chamber from being applied to the piston seal, thereby protecting the piston seal, and also prevent the failure of the hydraulic cylinder from this viewpoint. Thus, the durability of the hydraulic cylinder can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part showing one embodiment of a buffer structure for a hydraulic cylinder of the present invention.

FIG. 2 is an enlarged view of a part of FIG.

FIG. 3 is a diagram showing pressure characteristics obtained in the embodiment shown in FIG. 1;

FIG. 4 is a diagram showing an overview of a hydraulic cylinder provided with a conventional buffer structure.

5 is a sectional view of the hydraulic cylinder shown in FIG.

FIG. 6 is a cross-sectional view of relevant parts showing a form at the start of a cushion stroke in the hydraulic cylinder shown in FIG. 4;

FIG. 7 is a cross-sectional view of a main part showing a form at the end of a cushion stroke in the hydraulic cylinder shown in FIG. 4;

8 is a diagram showing pressure characteristics obtained by the conventional hydraulic cylinder buffer structure shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hydraulic cylinder 2 Cylinder tube 3 Head cover 4 Cylinder 4a Bottom side chamber 4b Rod side chamber 5 Piston 5a Piston rod 6 Oilway 6a Boss hole 7 Oilway 7a Oilway (throttle means) 8 Mounting part 9 Mounting part 21 Sealing member 22 Auxiliary Piston 23 Throttle hole (throttle means) 24 End face

Claims (4)

[Claims] 1. A hydraulic cylinder which divides the interior of a cylinder into two chambers by slidably mounting a piston connected to a piston rod in the cylinder,
When the piston is displaced within the cushion stroke section of at least one of the two chambers, the flow path of return oil from the one chamber is narrowed to generate a cushion pressure in the one chamber. A cushioning mechanism having a cushion mechanism for forming a chamber in a cushioning chamber, wherein the cushioning mechanism is mounted on the piston rod and has an outer diameter substantially equal to the outer diameter of the piston; A hydraulic cylinder, comprising: an auxiliary piston disposed between one chamber and the piston; and throttle means provided in the auxiliary piston portion, the throttle means restricting an outflow path of return oil from the one chamber. Buffer structure. 2. An oil passage which is a gap formed between an outer peripheral surface of the auxiliary piston and an inner peripheral surface of the cylinder facing the auxiliary piston, wherein the throttle means is formed on the auxiliary piston, 2. A buffer structure for a hydraulic cylinder according to claim 1, further comprising a throttle hole which opens into said one chamber and communicates with said oil passage. 3. A buffer structure for a hydraulic cylinder according to claim 2, further comprising a seal member capable of sealing said oil passage with movement of said auxiliary piston in said one chamber direction. 4. The buffer for a hydraulic cylinder according to claim 3, wherein the seal member is a check seal member having a check function of preventing a flow of pressurized oil from the one chamber into the oil passage. Construction.