JPH11108014A - Driving circuit for hydraulic cylinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving circuit for a hydraulic cylinder, capable of making cushion pressure generated in a cushion mechanism into the minimum required cushion pressure. SOLUTION: A driving circuit has a hydraulic cylinder 1 with a cushion mechanism, a hydraulic pump P, a direction control valve 20 to control the flow of operating oil supplied from the hydraulic pump P to the hydraulic cylinder 1 and a pressure control means to change the pressure of pressure oil supplied to the hydraulic cylinder 1 depending on the size of cushion pressure generated in a rod-side chamber 4b or a bottom-side chamber 4a in the hydraulic cylinder 1. The pressure control means contains selection valves 22, 23 to detect the size of the cushion pressure generated in the chambers 4b, 4a and output it as a pilot pressure signal and a variable relief valve 21 to vary the discharge pressure of the hydraulic pump P to be gradually smaller as a value for the pilot pressure signal output from the selection valves 22, 23 are larger.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic cylinder provided in a construction machine such as a hydraulic shovel and having a cushion mechanism and a hydraulic pump for supplying hydraulic oil for driving the hydraulic cylinder. Circuit.

[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 cushion mechanism using hydraulic pressure is often provided to absorb such an impact.

FIGS. 4 to 8 are explanatory views showing an example of a drive circuit of a conventional hydraulic cylinder having such a cushion mechanism. FIG. 4 is a view showing an overview of the hydraulic cylinder, and FIG. 5 is shown in FIG. FIG. 6 is a cross-sectional view of a main part of a hydraulic cylinder drive circuit showing an operation mode at the start of a cushion stroke in the hydraulic cylinder shown in FIG. 4, and FIG. 7 is a cross-sectional view of the hydraulic cylinder shown in FIG. And FIG. 8 is a view showing pressure characteristics obtained by a cushion mechanism included in the conventional hydraulic cylinder shown in FIG.

In FIGS. 4 and 5, reference numeral 1 denotes a hydraulic cylinder, for example, a boom cylinder provided in a hydraulic shovel. The hydraulic cylinder 1 has a cylinder tube 2. One end of the cylinder tube 2 is closed and the other end is open, and a head cover 3 is attached to the open end. The cylinder 4 is constituted by the cylinder tube 2 and the head cover 3 described above. 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. A piston rod 5a is connected to the piston 5, and the piston rod 5a is led out of the head cover 3 to 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 reduction is provided with a boss hole 10 as a fitting portion at the closed side end of the cylinder tube 2 to open the oil passage 6 into the boss hole 10 and protrude from the end face of the piston 5. A boss 11 having an outer diameter that is inserted into the boss hole 10 with a small gap is provided. As a result, when the piston rod 5a enters the cylinder 4 and the piston 5 is displaced in the contracting direction and reaches near the end of its stroke, the boss 11
0, and at this time, the bottom chamber 4
Due to the restriction of the flow path from a to the oil path 6, pressure is generated in the bottom chamber 4a. This pressure increases according to the fitting length of the boss 11 into the boss hole 10. This pressure becomes the cushion pressure, and decelerates the piston 5 to absorb the impact.

On the other hand, as the cushion mechanism on the extension side,
A cushion ring 12 is provided. The distal end of the head cover 3 is inserted into the opening end of the cylinder tube 2, whereby the rod-side chamber 4 b has a stepped shape.
The portion to be inserted into the connector is 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 fitted into the head cover 3 near the stroke end, and the flow path formed by the annular gap therebetween is narrowed. The pressure in the side chamber 4b rises, and a cushion pressure is generated. 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 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 rises, and the piston 5 is slid and displaced in the cylinder 4 toward the head cover 3 by the action of this pressure, and the piston rod 5a connected to the piston 5 is extended. . At this time, since the rod side chamber 4b is connected to the tank T, the hydraulic oil in the rod side chamber 4b returns to the hydraulic oil tank T from the oil path 7 through the gap between the piston rod 5a and the head cover 3. I do.

As shown in FIG. 6, when the cushion cylinder 12 enters the cushion stroke area in the extension direction of the hydraulic cylinder 1, the cushion ring 12 is fitted into the head cover 3. As a result,
The flow path from the rod side chamber 4b to the oil path 7 has a flow path cross-sectional area of a diameter difference between the outer diameter of the cushion ring 12 and the inner diameter of the head cover 3, and the flow path of the return oil from the rod side chamber 4b. Squeezed. As a result, the flow rate of the return oil to the tank T 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. Further, the configuration shown in FIG. 7 is a configuration at the time of the stroke end in the extension direction of the piston rod 5a, and a period during which the piston 5 is displaced from the configuration in FIG. 6 to the configuration in FIG. 7 is a cushion stroke section. In the cushion stroke section, when the fitting length between the cushion ring 12 and the head cover 3 is increased, the throttle flow path of the return oil is correspondingly increased, and the cushion pressure in the cushion chamber is increased. , Almost all the load applied to the hydraulic cylinder 1 is absorbed.

[0010] The cushion pressure according to the prior art described above varies as shown in FIG. That is, the return oil flow path is an annular flow path due to the difference in diameter between the outer diameter of the cushion ring 12 and the inner diameter of the head cover 3, and the length of the flow path changes according to the cushion stroke. 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 the maximum load is applied to the hydraulic cylinder 1, it is necessary to provide a cushion characteristic in which the load can be substantially absorbed 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. The tube 2, the piston rod 5a, the piston 5, the thread connecting the piston rod 5a and the piston 5, and the head cover 3 will be damaged.

Reference numeral 19 shown in FIG. 5 is a relief valve for uniquely setting the discharge pressure of the hydraulic pump P. In FIG. 5, a directional control valve arranged between the hydraulic pump P, the tank T, and the hydraulic cylinder 1 to control the flow of the hydraulic oil discharged from the hydraulic pump P is not shown.

[0012]

By the way, in the cushion mechanism of the hydraulic cylinder, as described above, there is a demand for securing a cushion characteristic capable of absorbing the entire load as much as possible by the cushion pressure in the cushion stroke region. This demand can be relatively easily met by increasing the cushion stroke. However, in this case, the total length of the hydraulic cylinder 1 is increased, which is not practical in terms of the construction machine. Therefore, in consideration of shortening the cushion stroke and absorbing a large load, the diameter difference between the cushion ring 12 and the head cover 3,
That is, the annular gap is set to be sufficiently small (for example, the technique described in Japanese Utility Model Laid-Open No. 6-62207).

However, in the prior art shown in FIGS. 4 to 7 and the prior art shown in the above publication, FIGS.
The hydraulic cylinder 1 is continuously supplied with the discharge pressure of a hydraulic pump P uniquely set by a relief valve 19, that is, for driving a working machine of the hydraulic shovel. The same pushing force corresponding to the relatively large pressure set by the relief valve 19 is continuously applied to the piston 5 over the entire stroke of the hydraulic cylinder 1, and the cushion pressure tends to increase. This tends to generate an unnecessarily high cushion pressure. Along with this, the accuracy of stopping the movement of the piston 5 so as to match the stroke end, that is, the buffering accuracy tends to be coarse.

Further, as described above, since the cushion pressure tends to be high and the cushioning accuracy tends to be coarse, the conventional technique described above requires a cushion ring at the end of the cushion stroke when the hydraulic cylinder 1 is extended. 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 situation in the prior art, and has as its object to provide a hydraulic cylinder drive circuit capable of suppressing a cushion pressure generated in a cushion mechanism to a minimum required cushion pressure. 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. A hydraulic cylinder partitioned into two chambers, and an outflow of return oil from the one chamber when the piston is displaced into a cushion stroke area of at least one of the two chambers. In a hydraulic cylinder drive circuit having a cushion mechanism that narrows the flow path to generate a cushion pressure in the one chamber, forms the one chamber in the cushion chamber, and a hydraulic pump that supplies pressure oil for driving the hydraulic cylinder. A pressure adjusting means for changing the magnitude of the pressure of the pressure oil supplied to the hydraulic cylinder in accordance with the magnitude of the cushion pressure. A.

According to the first aspect of the present invention, the piston of the hydraulic cylinder is displaced into the cushion stroke region by the pressure oil discharged from the hydraulic pump,
When the cushion pressure is generated by the cushion mechanism, the pressure adjusting means responds to the cushion pressure according to the cushion pressure.
Control is performed so that the magnitude of the pressure of the pressure oil supplied to the hydraulic cylinder changes. For example, as the cushion pressure gradually increases by this pressure adjusting means, the pressure of the hydraulic oil supplied to the hydraulic cylinder is reduced to the pressure given for driving the hydraulic cylinder before the piston enters the cushion stroke area. It is controlled so that it becomes lower gradually. As a result, the pushing force of the piston is reduced as compared with the size before the piston enters the cushion stroke area, and the cushion pressure generated in the cushion chamber is reduced to a minimum necessary within a range capable of substantially absorbing the load applied to the hydraulic cylinder. The pressure can be reduced to the cushion pressure.

According to a second aspect of the present invention, in the first aspect of the present invention, the pressure adjusting means includes a variable relief valve for variably controlling the discharge pressure of the hydraulic pump. It is.

According to the second aspect of the present invention, the set pressure of the variable relief valve is changed by the cushion pressure. For example, as the cushion pressure gradually increases, the set pressure of the variable relief valve is controlled so as to gradually decrease, and the discharge pressure of the hydraulic pump changes so as to gradually decrease. As a result, the pressure of the hydraulic oil supplied to the hydraulic cylinder gradually decreases, and as described above, the pushing force of the piston is reduced as compared with the size before the piston enters the cushion stroke area, and the cushion generated in the cushion chamber is reduced. The pressure can be suppressed to the minimum necessary cushion pressure within a range capable of substantially absorbing the load applied to the hydraulic cylinder.

According to a third aspect of the present invention, in the second aspect of the present invention, the pressure adjusting means includes a selection valve for detecting the cushion pressure.

According to the third aspect of the present invention, the cushion pressure is detected by the selection valve, and the drive of the variable relief valve is controlled by the detection signal of the selection valve.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a hydraulic cylinder drive circuit according to the present invention will be described below with reference to the drawings. 1 to 3 are explanatory views showing an embodiment of a hydraulic cylinder drive circuit of the present invention, for example, a hydraulic cylinder drive circuit provided in a hydraulic shovel. FIG. 1 shows this embodiment before entering a cushion stroke area. FIG. 2 is a cross-sectional view of a main part showing one embodiment when a cushion stroke is entered, and FIG. 3 is a view showing a pressure characteristic obtained in the embodiment shown in FIGS. 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 is formed by partitioning a cylinder 4 including a cylinder tube 2 and a head cover 3 into two chambers, that is, a bottom chamber 4a and a rod chamber 4b. And a piston rod 5a connected to the piston 5.

One end of the above-described 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 1 communicating with the oil passage 6 are provided on the bottom side chamber 4a.
0 is provided, and an oil path 7 for supplying and discharging pressure oil is provided on the side of the rod-side chamber 4b.

At the end of the piston rod 5a located in the cylinder tube 2, there is provided a boss 11 which can be inserted into the boss hole 10. These boss 11 and boss hole 1
0 forms a cushion mechanism when return oil is discharged from the bottom chamber 4a, that is, when the bottom chamber 4a becomes a cushion chamber.

A cushion ring 12 is mounted on the piston rod 5a located on the head cover 3 side of the piston 5, and this cushion ring 12 can be fitted into a hole formed in the head cover 3 and communicating with the oil path 7. It has become. That is, the outer diameter of the cushion ring 12 is slightly smaller than the inner diameter of the head cover 3.
The hole in the head cover 3 and the cushion ring 12 constitute a cushion mechanism when return oil is discharged from the rod-side chamber 4b, that is, when the rod-side chamber 4b becomes a cushion chamber. In FIGS. 1 and 2, reference numeral 5c denotes a gap between the outer peripheral surface of the piston 5 and the inner peripheral surface of the cylinder tube 2 so that the inside of the cylinder tube 2 is divided into the above-described two chambers. 2 shows a piston seal for sealing the piston seal.

P is a hydraulic pump for supplying hydraulic oil for driving the hydraulic cylinder 1, T is a tank, 20 is a hydraulic pump P, disposed between the tank T and the hydraulic cylinder 1, and is discharged from the hydraulic pump P. It is a directional control valve for controlling the flow of pressurized oil.

In particular, in the present embodiment, there is provided a pressure adjusting means for changing the magnitude of the cushion pressure generated in the cushion chamber formed in the bottom chamber 4a and the rod chamber 4b. The pressure adjusting means detects, for example, the magnitude of a cushion pressure generated in a cushion chamber formed in the rod side chamber 4b and outputs the pilot pressure signal as a selection valve 22, and a cushion formed in the bottom side chamber 4a. A selection valve 23 that detects the magnitude of the cushion pressure generated in the chamber and outputs the same as a pilot pressure signal, and a hydraulic pressure corresponding to the magnitude of the value of the selection valve 22 or the pilot pressure signal output from the selection valve 23. A variable relief valve 21 capable of changing the discharge pressure of the pump P. For example, the opening of the variable relief valve 21 is increased and the discharge pressure of the hydraulic pump P is set to gradually decrease as the value of the pilot pressure signal output from the selection valves 22 and 23 increases.

The operation of the embodiment configured as described above is as follows. When the hydraulic cylinder 1 performs the extension operation, that is, the direction control valve 20 is switched to the right position as shown in FIGS. 1 and 2, and the oil passage 6 of the hydraulic cylinder 1 communicates with the hydraulic pump P via the direction control valve 20. , The oil passage 7 communicates with the tank T via the directional control valve 20, and the hydraulic pump P
Is supplied to the bottom chamber 4a through the oil passage 6 and the boss hole 10, the pressure of the hydraulic oil supplied to the bottom chamber 4a
The piston 5 moves to the left in FIG. At this time, the return oil from the rod-side chamber 4b is simultaneously returned to the tank T through the oil path 7.

Conversely, when the hydraulic cylinder 1 performs the contracting operation, that is, the direction control valve 20 is switched from the state shown in FIGS. 1 and 2 to the left position, and the oil passage 7 of the hydraulic cylinder 1 To the hydraulic pump P through the oil passage 6
Communicates with the tank T via the direction control valve 20, and the hydraulic oil discharged from the hydraulic pump P passes through the gap between the oil path 7, the wall surface of the hole of the head cover 3 and the outer peripheral surface of the piston rod 5a to the rod side chamber 4b. When supplied, the piston 5 moves rightward in FIG. 1 by the pressure of the hydraulic oil supplied to the rod-side chamber 4b. At the same time, the return oil from the bottom chamber 4a is returned to the tank T through the oil path 6.

During the extension operation of the hydraulic cylinder 1 described above, for example, during the extension operation, the piston 5 moves to the left in FIG.
When 2 starts to be fitted into the hole of the head cover 3, it enters the cushion stroke area in this extension operation, and the cushion stroke is started. With the subsequent leftward movement of the piston 5 and the cushion ring 12,
A cushion pressure is generated in the rod side chamber 4b, and the cushion pressure gradually increases. This cushion pressure is applied to the left end face of the piston 5, 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.

While such an operation is being performed, the cushion pressure generated in the rod side chamber 4b is detected by the selection valve 22 as described above, and is output to the drive unit of the variable relief valve 21 as a pilot pressure signal. The opening amount of the variable relief valve 21 gradually increases as the cushion pressure generated in the rod side chamber 4b gradually increases, whereby the discharge pressure of the hydraulic pump P gradually decreases. Therefore, the pressure of the hydraulic oil supplied to the bottom chamber 4a of the hydraulic cylinder 1 is gradually reduced as compared with the pressure applied for driving the hydraulic cylinder 1 before the piston 5 enters the cushion stroke area. Is controlled. Accordingly, the pushing force at the time of the extension operation of the piston 5 is reduced as compared with the size before the piston 5 enters the cushion stroke area, and the rod-side chamber 4 b
Can be controlled to the minimum necessary cushion pressure within a range that can substantially absorb the load applied to the hydraulic cylinder 1.

When the directional control valve 20 is switched to the left position in FIG. 2 from the state in which the hydraulic cylinder 1 is extended as described above, and the operating oil of the hydraulic pump P is supplied to the oil passage 7, the hole in the head cover 3 is opened. Hydraulic fluid flows from a gap between the wall surface of the piston rod 5a and the outer peripheral surface of the piston rod 5a and presses the end surface of the cushion ring 12, thereby moving the piston 5 rightward, and then the hydraulic fluid flows into the rod side chamber 4b. Then, the piston 5 subsequently moves rightward. When the cushion ring 12 comes out of the hole of the head cover 3 and goes out of the cushion stroke area during the extension operation, the drive unit of the variable relief valve 21 communicates with the tank T, and the variable relief valve 21 changes to a predetermined maximum set pressure. Thus, the discharge pressure of the hydraulic pump P is maintained at a predetermined maximum set pressure.
The hydraulic oil at the highest set pressure is continuously supplied to the rod side chamber 4b via the oil path 7 and the like, and the piston 5 is moved rightward with a relatively large pushing force to perform a contracting operation. Further, the piston 5 moves rightward in FIG.
When 1 starts to be fitted into the boss hole 10, the cushion stroke area in the contracting operation is entered, and the cushion stroke is started. With the subsequent rightward movement of the piston 5, a cushion pressure is generated in the bottom chamber 4a, and this cushion pressure gradually increases. This cushion pressure is applied to the right end surface of the piston 5, and a leftward 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 contraction operation of the hydraulic cylinder 1 ends.

While such an operation is being performed, the bottom chamber 4 is operated in the same manner as during the above-described extension operation.
a is detected by the selection valve 23,
The pilot pressure signal is output to the drive unit of the variable relief valve 21. The opening amount of the variable relief valve 21 gradually increases as the cushion pressure generated in the bottom chamber 4a gradually increases, so that the discharge pressure of the hydraulic pump P gradually decreases. Therefore, the hydraulic cylinder 1
Pressure of the hydraulic oil supplied to the rod side chamber 4b of
The pressure is controlled so as to become gradually lower than the pressure applied for driving the hydraulic cylinder 1 before the piston 5 enters the cushion stroke region. Along with this, the pushing force at the time of the contraction operation of the piston 5 is reduced as compared with the magnitude before the piston 5 enters the cushion stroke area, and the cushion pressure generated in the bottom chamber 4 a is reduced by the load applied to the hydraulic cylinder 1. The cushion pressure can be suppressed to the minimum necessary pressure within a range that can be substantially absorbed.

The solid line in FIG. 3 shows the relationship between the stroke in the cushion stroke region and the cushion pressure when the hydraulic cylinder 1 is extended or contracted, that is, the pressure characteristic obtained in the present embodiment. As shown in FIG. 3, the cushion pressure at the end of the stroke can be suppressed lower than the cushion pressure in the above-described conventional technology indicated by the two-dot chain line.

When the directional control valve 20 is switched from the state in which the hydraulic cylinder 1 is contracted to the right position in FIG.
When 1 comes out of the boss hole 10 and deviates from the cushion stroke area at the time of the contraction operation, the drive unit of the variable relief valve 21 communicates with the tank T, and the variable relief valve 21 is changed to a predetermined maximum set pressure, The discharge pressure of the pump P is again maintained at the predetermined maximum set pressure. The hydraulic oil at the highest set pressure is continuously supplied to the bottom chamber 4a via the oil path 6, and the piston 5 is moved to the left with a relatively large pushing force, so that the extension operation as described above can be performed.

In the present embodiment configured as described above, as described above, the cushion pressure generated in the cushion stroke area during the extension operation or the contraction operation of the hydraulic cylinder 1 can be suppressed low. The pushing force applied to the piston 5 at the stroke end due to the pressure can be made relatively small, so that it is relatively easy to stop the piston 5 so as to coincide with the stroke end, and it is possible to obtain excellent cushioning. Accuracy can be obtained.

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

Also, since the cushion pressure can be kept relatively low, the load on the components of the hydraulic cylinder 1 such as the piston 5, the piston seal 5c mounted on the piston 5, the piston rod 5ba can be reduced.
Thereby, damage to the components of the hydraulic cylinder 1 can be prevented from a different viewpoint from the above, and the durability of the hydraulic cylinder 1 can be improved.

In the above-described embodiment, the selection valves 22 and 23 for detecting the cushion pressures of the two chambers of the hydraulic cylinder 1, ie, the rod-side chamber 4b and the bottom-side chamber 4a, are provided, and the extension operation of the hydraulic cylinder 1 is performed. Time,
Although the configuration is such that the cushion pressure is suppressed both during the contraction operation, the magnitude of the pressure of the pressure oil supplied to the hydraulic cylinder 1 only during the extension operation depends on the type of work performed by the hydraulic cylinder 1 and the like. The configuration may be such that pressure adjusting means for changing the pressure is provided, or conversely, pressure adjusting means for changing the magnitude of the pressure of the pressure oil supplied to the hydraulic cylinder 1 only during the contraction operation may be provided.

[0041]

As described above, according to the present invention, the cushion pressure generated in the cushion mechanism can be suppressed to the minimum required cushion pressure. It is relatively easy to stop the pistons so that they coincide with each other, and it is possible to obtain superior cushioning accuracy as compared with the related art. Also,
Since such excellent buffering accuracy is obtained, it is possible to prevent collision between the piston and the head cover, prevent a failure of the hydraulic cylinder due to such a collision, and improve the durability of the hydraulic cylinder in comparison with the related art. Can be improved.

Also, since the cushion pressure can be kept relatively low, the load on the components of the hydraulic cylinder such as the piston, the piston seal mounted on the piston, and the piston rod can be reduced. In view of the above, the components of the hydraulic cylinder can be protected, and the durability of the hydraulic cylinder can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part showing an embodiment of a drive circuit of a hydraulic cylinder of the present invention, particularly showing an operation mode before entering a cushion stroke region.

FIG. 2 is a cross-sectional view of a main part showing an embodiment of a drive circuit for a hydraulic cylinder of the present invention, particularly showing an operation mode when a cushion stroke region is entered.

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

FIG. 4 is a diagram showing an overview of a conventional hydraulic cylinder.

FIG. 5 is a sectional view of a main part of a drive circuit of the hydraulic cylinder shown in FIG. 4;

6 is a cross-sectional view of a principal part showing an operation mode at the start of a cushion stroke in the hydraulic cylinder shown in FIG.

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

FIG. 8 is a diagram showing pressure characteristics obtained by a cushion mechanism included in the conventional hydraulic cylinder 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 5c Piston seal 6 Oil path 7 Oil path 8 Mounting part 9 Mounting part 10 Boss hole 11 Boss 12 Cushion ring 20 Directional control valve 21 Variable relief valve (pressure adjusting means) 22 Selection valve (pressure adjusting means) 23 Selection valve (pressure adjusting means) P Hydraulic pump T Tank

Claims (3)

[Claims] 1. A hydraulic cylinder which partitions a cylinder into two chambers by slidably mounting a piston connected to a piston rod in the cylinder, and a hydraulic cylinder provided in the hydraulic cylinder, wherein the piston is When displaced within the cushion stroke area of at least one of the chambers, the flow path of the return oil from the one chamber is narrowed to generate cushion pressure in the one chamber, and this one chamber is used as a cushion chamber. In a hydraulic cylinder drive circuit having a cushion mechanism to be formed and a hydraulic pump for supplying hydraulic oil for driving the hydraulic cylinder, the pressure of the hydraulic oil supplied to the hydraulic cylinder according to the magnitude of the cushion pressure A hydraulic cylinder drive circuit comprising a pressure adjusting means for changing a size. 2. A hydraulic cylinder drive circuit according to claim 1, wherein said pressure adjusting means includes a variable relief valve for variably controlling a discharge pressure of said hydraulic pump. 3. The hydraulic cylinder drive circuit according to claim 2, wherein said pressure adjusting means includes a selection valve for detecting said cushion pressure.