JPH0641763B2 - Fluid cylinder cushion device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cushion device for a fluid pressure cylinder used for shutting off a high speed emergency shutoff valve, and more particularly to a high speed operation of the fluid pressure cylinder. The impact is effectively alleviated at the stroke end, and the bounce phenomenon at the stroke end is eliminated.

(B) Background of technology Ultra-high vacuum systems such as accelerators and plasma experimental devices that accelerate electrons or protons to near the speed of light are equipped with a large number of measurement stations for various research purposes. A high-speed emergency shutoff valve is provided in the branch vacuum system that connects the ultra-high vacuum system and each measuring station. This is because at the measuring station, when the atmosphere with more than the exhaust capacity invades due to operation mistake or other accidents, it is detected promptly and the high-speed emergency shutoff valve is activated to shut off the branch vacuum system. This is to prevent the accident of air intrusion into the ultra-high vacuum system.

Conventionally, as such a technique, for example, JP-A-59-2
It is known in Japanese Patent No. 26774.

On the other hand, this type of emergency shutoff valve, especially the emergency shutoff valve used for small accelerators for experiments in laboratories, etc., is used from the time the sensor detects the intrusion of the atmosphere until the shutoff valve is fully closed. Is required to be 10 msec or less. In addition, the means to operate the emergency shutoff valve at high speed
It is desirable to use a pneumatic cylinder having a shock absorbing function from the viewpoints of handleability, economy, and the fact that air pressure can be easily obtained by using an exhaust device for ultra-high vacuum.

(C) Conventional technology Conventionally, as a pneumatic cylinder with a shock absorbing function,
The one disclosed in Japanese Patent Laid-Open No. 52-6884 is known.

The above-mentioned pneumatic cylinder cushion device exhausts the exhaust relief valve that opens when the pressure of the air trapped between the piston and the end cover rises to the set value, and the air whose pressure has risen to the set value immediately before the end of the piston end stroke. It is provided with a short-circuit exhaust passage which is released to the port.

According to this cushion device, when the piston reaches the cushion stroke region, the air pressure between the piston and the end cover suddenly increases, and this pressure is maintained just before the end of the stroke, and the relief valve is opened near the end of the stroke to rapidly increase the pressure. As a result, it becomes possible to exert an effective cushioning action in a short stroke without causing a bounce phenomenon at the end of the stroke.

(D) Problems to be Solved by the Invention In the conventional cushion device as described above, the relief valve and the short-circuit passage are used to absorb the shock with a short stroke which is only a fraction of the piston stroke. There is a limit to the amount of kinetic energy that can be absorbed in order to exert an effective cushioning effect, and at most 1000-
It can be applied only to a cylinder having an operating speed of about 2000 mm / sec. Further, when the operating speed is equal to or higher than the above operating speed, the pressure in the volume reducing side cylinder chamber cannot be increased to a pressure necessary to absorb the kinetic energy of the piston in a cushion stroke which is a fraction of the piston stroke. If the pressure in the cylinder chamber on the volume reducing side is increased by extremely narrowing the relief valve and the short-circuit passage, exhaust resistance will increase and the peak pressure at the end of the stroke will become extremely high, which causes a bounce phenomenon. As a result, speed control becomes difficult, and an effective cushioning effect cannot be exerted.

That is, in the conventional cushion device as described above, 600
It cannot be applied to impact relaxation of a cylinder operating at a high speed of 0 mm / sec, and cannot be used as a cylinder device for a high-speed emergency shutoff valve of the ultra-high vacuum system as described above.

Further, in the above-mentioned conventional cushion device, the pressure in the volume reducing cylinder chamber is increased to a level sufficient to absorb the kinetic energy of the piston, and the pressure near the end of the stroke is released to the atmosphere to provide a sufficient cushion stroke. A method of using the entire stroke of the cylinder as the cushion stroke is also conceivable to secure it, but with this, the cushion stroke is about the same length as the piston stroke, and the total length of the cylinder is almost doubled. There was a problem that shock relaxation without bounce phenomenon could not be realized.

The present invention has been made in order to solve the above-mentioned conventional problems, and it is possible to surely absorb the shock at the end of the stroke even at a high speed operation of about 6000 mm / sec and to provide a cushioning action without a bounce phenomenon. An object is to provide a cushion device for a fluid pressure cylinder.

(E) Means for Solving the Problems A cushion device for a fluid pressure cylinder according to the present invention is a low-pressure fluid source for holding a volume-reducing cylinder chamber in a pre-pressure state as the piston of the fluid pressure cylinder advances. And the exhaust passage of the volume reducing side cylinder chamber is closed by the fluid pressure of the low pressure fluid source and the fluid pressure in the volume reducing side cylinder chamber becomes equal to or higher than a set value due to the high speed advance of the piston. In this case, a check relief valve for generating a motion absorption energy amount which is opened as a pilot pressure, and a throttle means for limiting the discharge amount of the fluid pressure of the volume reducing cylinder chamber through the check relief valve are provided.

(F) Action In the present invention, when the piston is advanced at high speed, the pre-pressure fluid in the volume reducing side cylinder rises above the fluid pressure for advancing the piston, and the pressure in the volume reducing side cylinder chamber is increased. Increasing the pressure in the pre-pressure state is more efficient and can be performed in a shorter time than setting the pressure in the volume reducing cylinder chamber to atmospheric pressure. This pressure increase surely generates the kinetic absorption energy for braking against the forward kinetic energy of the piston to effectively absorb the impact at the stroke end, and at the same time, the check relief valve opens and the compressed high pressure fluid in the cylinder chamber on the volume reduction side is opened. It is possible to smoothly stop the piston at the stroke end by discharging it through the throttle means.

In addition, in order to advance the piston at high speed when the cylinder chamber on the volume reducing side is held in the pre-pressure state,
In order to move the piston forward, it is necessary to generate a large pressure difference in both chambers of the piston in a short time.Therefore, a highly responsive switching valve and a tank (accumulation chamber) are combined and connected to the other chamber of the piston. This is achieved by inflowing a high-pressure fluid within an extremely short time.

(G) Embodiment of the Invention An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 is a diagram showing the principle configuration of a high-speed cylinder device provided with a cushion device according to the present invention, which is roughly classified into a cylinder main body 1 that makes a stroke motion with a fluid pressure such as air, and a pressure accumulating chamber that constantly stores fluid at a predetermined pressure. 2, a high response electromagnetic two-way switching valve 3 for opening and closing the pressure accumulating chamber 2 and the head side space of the cylinder body 1, and an electromagnetic auxiliary control valve for controlling the forward movement and forward movement of the piston and its return control. 4 and a cushion pressure control mechanism 5 that communicates with the rod-side cylinder chamber of the cylinder body 1 and that alleviates the impact relaxation and bounce phenomenon at the stroke end.

As shown in FIG. 2, the cylinder body 1 includes a cylinder tube 11 having an opening on the rod side, a rod cover 12 closing the opening of the cylinder tube 11, and a cylinder tube 11 slidable in the longitudinal direction thereof. It is composed of a movably fitted piston 13 and a piston rod 14 which is integrally connected to the piston 13 and which penetrates the rod cover 12 and projects outward, and projects inside the rod cover 12. A rubber damper 1 is provided on the end surface of the boss portion 12a provided to alleviate the collision with the piston 13.
5 is fixed to the cylinder tube 11 facing the outer periphery of the boss portion 12a, and the rod-side cylinder chamber 18a communicates with the cushion pressure control mechanism 5.
6 is formed. Reference numeral 19 is a space formed in the cylinder chamber 18a when the piston 13 reaches the forward end where it abuts against the rubber damper 15, and this space 19 compensates for a processing error of the reduced volume of the cylinder chamber 18a due to the forward movement of the piston 13. This is for obtaining a stable cushioning effect.

The two-way switching valve 3 is mounted on the end surface of the cylinder body 1 on the head side cylinder tube as shown in FIGS. 1, 2 and 4, and is formed at the center of the head side bottom portion 11a of the cylinder tube 11. A valve seat 31 airtightly fitted to the provided opening 17 and a plurality of valve openings 31 formed in the valve seat 31.
A movable disk 32 for opening and closing a and the movable disk 32
Is provided with a spring member 33 for constantly pressing the valve seat 31 to urge the valve opening 31a to a closed state, and a solenoid 34 for attracting the movable disk 32 in the opening direction. Fixed iron core 3 having a high pressure fluid inflow passage 35a for communicating the valve seat 31 and the pressure accumulating chamber 2 on the central axis
5 and an exciting coil 36 wound around this, a cylindrical cover 37 is airtightly fitted to the outer periphery of the fixed iron core 35 including the outer peripheral surface of the exciting coil 36, and the tip portion of the cover 37 is provided. Is connected to the outer end of the bottom of the cylinder tube 11 to fix the solenoid 34 to the cylinder body 1. Also, the solenoid 34
The outer periphery of the cylinder tube 11 is sealed by a cover 38 fixed to the outer end surface of the bottom of the cylinder tube 11, and a container 21 is fixed to the cover 38 so that a space of a predetermined volume is formed on the outer periphery of the cover 38. The chamber 2 is formed. An inflow port 22 that communicates with an external fluid pressure source 6 such as air pressure is formed in the container 21 forming the pressure accumulation chamber 2, and the high pressure (4 kgf) from the fluid pressure source 6 enters the pressure accumulation chamber 2 through the port 22.
/ Cm ² ) of fluid is always accumulated.

The auxiliary control valve 4 is fixed to a valve block 51 of a cushion pressure control mechanism 5 described later as shown in FIGS. 2 and 3, and has a fluid inflow port 41, an outflow port 42 and a discharge port 43. Valve box 44 and this valve box 4
4, a spool 45 that is slidably fitted in the switch 4, and connects the outflow port 42, the inflow port 41, and the discharge port 43 to each other, a solenoid 46 that operates the spool 45, and a return spring 47. The inflow port 41 is a passage 52 formed in the valve block 51.
Is communicated with the fluid pressure source 7 through the flow port, and the outflow port 42 is provided with a passage 53 formed in the valve block 51.
Also, it is communicated with the head side cylinder chamber 18b of the cylinder body 1 through a passage 11b formed in the cylinder tube 11.

Further, the cushion pressure control mechanism 5 has a valve block 51 fixed to the outer periphery of the cylinder body 1 as shown in FIG.
The valve block 51 is provided with a check relief valve 54 which communicates the rod side cylinder chamber 18a with the atmosphere when the pressure in the rod side cylinder chamber 18a of the cylinder body 1 becomes equal to or higher than a set pressure.

The check relief valve 54 is provided in the rod side cylinder chamber 18a.
Cylindrical valve seat member 54 provided in passage 54a between
b and a movable disk 54d which is slidably fitted in the passage 54a and which opens and closes the opening of the discharge passage 54c formed in the valve seat member 54b and the low-pressure fluid supply port 56. A variable throttle valve 55 is provided on the atmosphere open side, and the variable throttle 55 is composed of a needle valve body 55a and a lock nut 55b thereof. Further, the port 56 has a low pressure (1.5 kgf
/ Cm ² ) connected to a fluid pressure source 8. The passage 54a through which the low-pressure fluid flows is provided with a check valve 5 as shown in FIG.
7 to communicate with the rod-side cylinder chamber 18a, and the pressure in the rod-side cylinder chamber 18a is changed to the pilot passage 58.
Is added to the movable disk 54d in the direction of opening the opening of the exhaust passage 54c. Therefore, when the piston 13 of the cylinder body 1 is at the retracted or retracted end, the low-pressure fluid pressure from the fluid pressure source 8 acts on the movable disc 54d and the movable disc 54d.
Is press-engaged with the opening of the valve seat member 54b to close the atmosphere side, and the fluid pressure source 8 is provided in the rod-side cylinder chamber 18a.
It is maintained at a pressure (1.5 kgf / cm ² ) according to the supply pressure of.
Further, the pressure in the rod side cylinder chamber 18a generated as the piston 13 moves forward is made to act on the valve seat member engaging side of the movable disc 54d as a pilot pressure through the pilot passage 58, and the compressed fluid pressure in the rod side cylinder chamber 18a is generated. Has reached a predetermined level and the pressure against the pressure receiving area of the movable disc 54d on the valve seat member engaging side is larger than the product of the pressure receiving area on the low pressure supply side of the movable disc 54d and the fluid pressure, The rod-side cylinder chamber 18a is slid to the supply port 56 side to communicate with the atmosphere through the variable throttle valve 55.

Next, the operation of this embodiment configured as described above will be described.

FIG. 2 shows a state in which the piston 13 has retracted and returned to the head side (right side in the figure). At this time, low pressure (1.5 kgf / c
The fluid pressure from the fluid pressure source 8 of m ² ) is the check relief valve 5
4 acts on the movable disc 54d of FIG. 4 to close the exhaust opening of the valve seat member 54b, and through the passage 54a, the check valve 57 and the passage 16, the rod side cylinder chamber 18a.
Is added to the inside of the cylinder chamber 18a to generate a low pressure, for example, 1.
Hold at a pressure of 5 kf / cm ² . Further, a high pressure (4 kgf / cm ² ) fluid is supplied from the fluid pressure source 6 into the pressure accumulating chamber 2,
As a result, the pressure in the pressure accumulating chamber 2 is maintained at a fluid pressure sufficient to operate the cylinder body 1 at high speed. The solenoid 34 of the two-way switching valve 3 is demagnetized, and the movable disk 32 is pressed against the valve seat 31 by the spring member 33, so that the pressure accumulating chamber 2 and the head side cylinder chamber 18b are shut off from each other. Similarly, since the solenoid 46 of the auxiliary control valve 4 is also in the demagnetized state, the inflow port 41 is closed, the outflow port 42 and the exhaust port 43 are in communication, and the head side cylinder chamber 18b is open to the atmosphere.

Next, when the solenoid 34 of the two-way switching valve 3 is energized and excited, the movable disc 32 is separated from the valve seat 31 against the spring member 33 and adsorbed to the fixed iron core 35. As a result, when the valve opening 31a opens as the movable disc 32 separates from the valve seat 31, the high-pressure fluid in the pressure accumulating chamber 2 passes through the passage 3
5a, through the valve opening 31a of the valve seat 31, and suddenly flows into the head side cylinder chamber 18b, and the piston 13 is rapidly advanced to the rod side shown by the arrow A in FIG.

In addition, in order to obtain the high responsiveness of the two-way switching valve 3, a large current is temporarily passed through the exciting coil 36. Coil 36 at this time
The value of the electric current that flows in is 600 A, and the energizing time is 100 msec.
Is.

At the same time that the two-way switching valve 3 is energized, the solenoid 46 of the auxiliary control valve 4 is also energized.
Is operated to connect the inflow port 41 and the outflow port 42, and the high pressure (4 kgf / cm ² ) fluid from the fluid pressure source 7 flows into the head side cylinder chamber 18b through the passage 52, the ports 41, 42 and the passage 11b. Let The fluid pressure at this time hardly functions in the rapid forward movement of the piston 13 toward the rod side, and is for holding the piston 13 stably when the piston 13 reaches the stroke end.

FIG. 5 shows the displacement of the piston 13 (not shown but equivalent to an emergency shutoff valve of an ultra-high vacuum system connected to the piston 13) and the pressure change of the rod and the head side cylinder chambers 18a and 18b from the measured values. is there.

As is clear from the characteristic curve I in FIG. 5, the pressure in the head side cylinder chamber 18b is almost equal to zero immediately after the two-way switching valve 3 is opened, and when it reaches 0.2 msec, the pressure rises sharply to 0.25 msec. 4kgf equal to supply air pressure at the time
/ Cm ² is reached. Then, when the piston 13 starts to move forward, the pressure in the head side cylinder chamber 18b sharply drops to about 3 kgf / cm ² as shown by the characteristic curve I, and the characteristic curve I moves in accordance with the forward displacement of the piston 13 shown by the characteristic curve II below. Like

On the other hand, the rod side cylinder chamber 1 due to the forward movement of the piston 13
As the volume of 8a decreases, the cylinder chamber pressure becomes
As shown by the characteristic curve III in the figure, the pressure gradually increases from the pre-pressure point of 1.5 kgf / cm ² . And the two-way switching valve 3
When about 0.73 msec has elapsed since the opening command was given to the piston, the pressure in the rod side cylinder chamber 18a becomes larger than the pressure in the head side cylinder chamber 18b, and the piston 13 becomes The maximum pressure (4 kgf / cm ² ) is reached just before reaching the end of the stroke. When this pressure is reached, the movable disc 54d of the check relief valve 54, which uses this pressure as the pilot pressure, moves through the passage 54a.
The inside is moved to the port 56 side, and the exhaust opening of the valve seat member 54b is opened. Therefore, the compressed air in the rod side cylinder chamber 18a is discharged to the atmosphere through the pilot passage 58, the discharge passage 54c and the variable throttle valve 55. Along with this, the pressure in the rod side cylinder chamber 18a gradually decreases from the highest pressure point and changes to the low pressure fluid pressure level from the fluid pressure supply source 8 as shown by the characteristic curve III.

That is, in FIG. 5, the front region S1 surrounded by the characteristic curves I and III is the forward kinetic energy for advancing the piston 13 at high speed (6000 mm / sec), and the rear region S2 is for braking the piston 13 for high speed forward movement. Kinetic absorption energy, which effectively absorbs the impact at the stroke end of the piston 13 advanced at a high speed, and at the same time, the check relief valve 54 opens and the pressure in the rod side cylinder chamber 18 passes through the variable throttle valve 55 to the atmosphere. By discharging, the pressure in the cylinder chamber 18a is gradually reduced as shown by the characteristic curve III in FIG. 5, whereby the piston 13 can be smoothly moved to the stroke end without causing a bouncing phenomenon. Therefore, as shown in the characteristic curve II, the piston 13 has a smooth displacement characteristic without a bouncing phenomenon, and furthermore, the piston 13 is connected to a load of 310 g, that is, an emergency shutoff valve of an ultra-high vacuum system, and this is opened. As a result of actually measuring the time required to complete the fully closing operation, it was confirmed that the time was 10.85 msec or less. This is because the kinetic absorption energy for braking shown by the region S2 in FIG. 5 can be reliably generated with respect to the high speed forward kinetic energy of the piston 13.

When the piston 13 moved forward at the stroke end is returned to the retracted end shown in FIG. 2, the solenoid 46 of the auxiliary control valve 4 is stopped from being energized, and the spool 45 is returned by the spring 47 to return to the head side cylinder chamber 18b. To the atmosphere through the exhaust port 43. Therefore, the low-pressure fluid supplied from the external fluid pressure source 8 always flows into the rod-side cylinder chamber 18a through the check relief valve 54,
This moves the piston 13 to the right in FIG.
It will be held in the state shown in the figure. At this time, the discharge passage 54c of the check relief valve 54 has a movable disk 54d.
Closed by.

As described above, in the present embodiment, in order to hold the piston 13 in the rear end position, that is, in the pre-pressure state, the low pressure fluid for supplying the piston 13 with its position is supplied into the rod side cylinder chamber 18a. And that
When the solenoid of the two-way switching valve 3 is turned on by the signal when the vacuum of the device system is broken for some reason, the movable disk 32 is magnetically attracted upward, and the high pressure fluid in the pressure accumulating chamber 2 passes through the passage. 35a to valve opening 31 of valve seat 31
After passing through a, it flows into the head side cylinder chamber 18b at once. At this time, since there is a large pressure difference between the rod side cylinder chamber 18a and the head side cylinder chamber 18a, the piston 1
3 rapidly moves in the direction A in FIG.

At this time, if pressurized air does not flow into the rod-side cylinder chamber 18a, that is, if it is in the atmospheric pressure state, the piston 13 suddenly moves to the boss portion 12a of the rod-side cylinder chamber 18a.
It collides with (the left end shown in FIG. 2) or the piston rod 1
There is a risk that an emergency shutoff valve (not shown) attached to the tip side of 4 may be destroyed.

Therefore, it is necessary to have a function of urgently performing a valve closing operation and then rapidly and smoothly stopping the piston 3.

Therefore, low-pressure fluid is supplied into the rod-side cylinder chamber 18a, and when the piston 13 moves rapidly,
Since the pressure inside the rod side cylinder chamber 1a does not flow out to the outside due to the circuit configuration of FIG. 1, it rapidly rises.

Therefore, the moving speed of the piston 13 rapidly decreases beyond the distance required to close the valve.

Then, near the end of the stroke, the maximum pressure is reached,
The check relief valve 54 is actuated by this pressure, the compressed air in the rod side cylinder chamber 18a is discharged from the variable throttle valve 55 to the atmosphere, and the piston 13 is smoothly and quietly stopped to the end.

In this way, in the present embodiment, it is possible to obtain a cylinder device having a smooth stop function at its operating end, which is capable of instantaneously operating with the emergency shutoff valve without greatly affecting accidents such as vacuum breakage. it can.

In the above embodiment, the variable throttle valve 55 is used to smoothly stop the piston 13 without causing a stroke bounce phenomenon. In this case, there is an advantage that it is possible to compensate for the load condition connected to the piston 13, the cylinder device and other processing and assembly errors, but the present invention is limited to those using such a variable throttle valve. Instead, it may be a fixed orifice. Further, the auxiliary control valve 4 may be a manual two-way switching valve. Furthermore, the relief valve 54 that constitutes the cushion pressure control mechanism 5 is not limited to that of the embodiment. Further, the means for mitigating impact and preventing the bounce phenomenon of the present invention is not limited to the high speed cylinder device of 6000 mm / sec,
Of course, it can also be applied to a cylinder device of 6000 mm / sec or less.

(H) Effects of the Invention As described above, according to the present invention, the volume reduction side cylinder chamber is held in the pre-pressure state as the piston of the fluid pressure cylinder advances, and the volume reduction side cylinder chamber is exhausted by the pre-pressure pressure. It is possible to control the amount of kinetic energy absorbed and the bounce phenomenon at the stroke end of the piston by using a cushion pressure control mechanism that has a valve mechanism that closes the passage and opens with the pressure in the volume reduction chamber as the piston moves forward and an exhaust throttle means. As a result, even in a fluid cylinder that operates at a high speed of about 6000 mm / sec, the impact at the stroke end can be reliably mitigated, the bounce phenomenon can be prevented, and the cushioning effect of a fluid cylinder with a short stroke is effective. There is an effect that can be exhibited.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of a fluid pressure cylinder device having a cushion device according to the present invention, FIG. 2 is a vertical sectional side view showing a concrete embodiment of a cylinder device having the cushion device of the present invention, and FIG. Is a sectional view taken along line III-III in FIG.
FIG. 4 is an enlarged sectional view of a two-way switching valve portion according to the present invention,
FIG. 5 is a characteristic diagram showing experimental results of the device of the present invention. 1 …… Cylinder body, 11 …… Cylinder tube, 13
...... Piston, 14 ...... Piston rod, 18a ...... Rod side cylinder chamber, 18b ...... Head side cylinder chamber, 2
… Accumulator, 3 …… Electromagnetic two-way switching valve, 31 …… Valve seat, 3
2 ... Movable disk, 33 ... Spring member, 34 ... Solenoid, 4 ... Electromagnetic auxiliary control valve, 5 ... Cushion pressure control mechanism, 54 ... Check relief valve, 55 ... Variable throttle valve, 6, 7 ... High pressure fluid pressure source, 8 ... Low pressure fluid pressure source.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Motoichi Ogawa, Asahi Plant, Kurama Seiko Co., Ltd., No. 1,243, Kama number, Asahi City, Chiba Prefecture (72) Inventor, Kikuo Nakajima, 2-4, Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture (56) References Japanese Patent Laid-Open No. 51-141974 (JP, A) Japanese Patent Laid-Open No. 58-644 (JP, A) Japanese Utility Model Sho 58-38003 (JP, U)

Claims (2)

[Claims] 1. A high-pressure fluid source for operating a piston at high speed is connected to one end of a cylinder body through a switching valve, and a load is connected to a piston rod connected to the piston, and the load is moved by advancing the piston. In the fluid pressure cylinder to be operated, a low-pressure fluid source that holds the volume-reducing side cylinder chamber in a pre-pressure state is connected to the volume-reducing side cylinder chamber, and the low-pressure fluid is supplied to the exhaust passage of the volume-reducing side cylinder chamber. A check relief valve for generating kinetic energy absorption, which is closed by the fluid pressure of the fluid source and opens as a pilot pressure when the fluid pressure in the volume reduction side cylinder chamber becomes higher than a set value as the piston moves forward at high speed, and A throttle means for limiting the discharge amount of fluid pressure in the cylinder chamber on the volume reducing side through the check relief valve is provided. Cushion device of a fluid pressure cylinder, wherein the door. 2. A cushion device for a fluid pressure cylinder according to claim 1, wherein the throttle means comprises a variable throttle valve.