JPH05280504A - Fluid cylinder - Google Patents

Abstract

PURPOSE: To increase output power of a fluid cylinder, without changing a cylinder bore or without raising fluid pressure. CONSTITUTION: A cylinder unit 100 is partitioned into plural cylinder chambers 131, 132 by a partition member 103. The respective cylinder chambers contain pistons 113, 114 respectively. These pistons are fixed to one piston rod 200. In an output stroke, pressurized fluid is applied to the acting surfaces A1, A2 of the respective pistons in the respective cylinders. In a return stroke, pressurized fluid is supplied to a back surface B1 of only one of pistons in the plural cylinder chambers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid cylinder operated by a pressure fluid such as hydraulic pressure or compressed air, and more specifically, a plurality of cylinder chambers are formed in one cylinder unit and one piston is provided in each cylinder chamber. And a plurality of pistons are fixed to one piston rod. This fluid cylinder is used to increase the power output.

[0002]

2. Description of the Related Art The basic construction of a conventional fluid cylinder will be described with reference to FIG. The cylinder unit 10 has flanges 10A and 10B at both ends thereof, and has an upper cylinder cover 11 and a lower cylinder cover 12
And are fixed by bolts 16. A cylinder chamber 32 is formed inside the cylinder unit 10, and the piston 13 is slidably and liquid-tightly accommodated therein. The piston 13 is fixed by a nut 15 to one end of a piston rod 14 that is slidably and slidably inserted in a hole formed in the lower cylinder cover 12. Upper cylinder cover 1
1 is provided with a first flow hole 21 for causing the pressure fluid to act on the pressure surface A side of the piston in the cylinder chamber, and the lower cylinder cover 12 applies the pressure fluid to the rear surface B side of the piston in the cylinder chamber. The 2nd circulation hole 22 for making is provided. Further, in order to prevent fluid leakage, the piston has a piston ring 19, the upper cylinder cover has a seal 17, and the lower cylinder cover has seals 17, 18.
Are provided respectively.

Explaining the operation of the fluid cylinder, the pressure fluid is first supplied to the first circulation hole 21 of the upper cylinder cover 11 from the switching valve of the pressure fluid supply system (not shown) and then to the second fluid of the lower cylinder cover 12. The flow hole 22 communicates with the drain. Then, the piston 13 is pushed by the fluid to push out the piston rod 14, and the output stroke (power stroke) is performed. When the piston rod 14 reaches a predetermined position, a limit switch (not shown) operates to operate the switching valve, and the supply of the pressure fluid is stopped.
When the pressurizing work is completed, the switching valve is operated by the control device (not shown). Then, the pressure fluid is supplied to the rear surface side of the piston 13 in the cylinder chamber 32 through the second circulation hole 22, and the fluid on the pressurizing surface side of the piston 13 returns to the drain through the first circulation hole 21. In this way, the piston 13 is pushed in the direction opposite to the output stroke, and the return stroke is performed. In this case, the back surface B of the piston 13
The area on the side is smaller than the area on the side of the pressure surface A due to the cross-sectional area of the piston rod 14, but the difference is small, so the speed of the output stroke of the piston and the speed of the return stroke are almost the same.

FIG. 7 shows another example of a conventional fluid cylinder. In this example, the flanges 10A and 10B provided on the cylinder of the example of FIG.
Is sandwiched between the upper cylinder cover 11 and the lower cylinder 12 and fixed by a long bolt 16A, the operation of which is exactly the same as that of the cylinder shown in FIG.

[0005]

In order to increase the output of the fluid cylinder, there is no other method than increasing the pressure of the fluid supplied to the cylinder chamber or increasing the inner diameter of the cylinder unit. It was However, if the pressure of the fluid is increased, the piping for supplying the fluid must be able to withstand high pressure sufficiently, and the cylinder, cylinder cover, seal, etc. must also be of special high pressure, which reduces the cost. Becomes higher. Also,
There was a practical limit to raising the pressure. On the other hand, if the inner diameter of the cylinder is increased, the dimension of the cylinder in the diameter direction increases, and depending on the purpose of use, it may not be possible to make the size sufficiently large due to the limitation of the mounting location.

It is an object of the present invention to provide a fluid cylinder capable of increasing the output without increasing the pressure of the fluid and increasing the inner diameter of the cylinder.

A fluid cylinder according to the present invention includes a cylinder unit axially partitioned into a plurality of cylinder chambers by a partition member, a first cylinder cover fixed to one end of the cylinder unit, and a cylinder unit other than the cylinder unit. A second cylinder cover fixed to the end, a piston rod slidably supported by penetrating the partition member and the second cylinder cover, and liquid-tight in each cylinder chamber of the plurality of cylinder chambers. A piston slidably accommodated and having a pressure surface and a back surface, the piston fixed to the piston rod and the pressure fluid flowing into and out of the pressure surface side of the piston in each cylinder chamber; Fluid supply passage, a second fluid supply passage through which a pressure fluid flows in and out of a rear surface side of the piston of the first cylinder chamber of the plurality of cylinder chambers, And a vent hole to communicate with the outside of the cylinder unit the back side of the first piston of the cylinder chambers outside the cylinder chamber.

According to an embodiment of the present invention, a cylinder chamber adjacent to the first cylinder cover is a first cylinder chamber, and the first fluid supply passage is provided in the first cylinder cover. A first flow hole that connects the first pressure fluid supply pipe and the pressure surface side of the piston of the first cylinder chamber to each other, and the pressure surface side of the piston of the plurality of cylinder chambers, which are provided in the piston rod, are connected to each other. The second fluid supply passage is formed of a second communication hole that communicates the back side of the piston of the first cylinder chamber with the second pressure fluid supply pipe.

Further, according to another embodiment of the present invention,
A first cylinder chamber is provided adjacent to the first cylinder cover.
Cylinder chamber, and the first fluid supply path is the first
And a plurality of cylinder chambers provided outside the cylinder unit, and a first flow hole provided in the cylinder cover for communicating the first pressure fluid supply pipe with the pressurizing surface side of the piston of the first cylinder chamber. And a pipe for communicating the pressurizing surface side of the piston of each of the cylinder chambers, and the second fluid supply path communicates the rear surface side of the piston of the first cylinder chamber with the second pressure fluid supply pipe. It consists of a second flow hole.

[0010]

The pressure fluid supplied from the pressure fluid supply system passes through the first pressure fluid supply pipe through the switching valve to the first pressure fluid supply pipe.
Is supplied from the fluid supply passage to the pressure surface side of the piston in each cylinder chamber, and the output of a value obtained by multiplying the area of the pressure surface of the piston in the plurality of cylinder chambers by the fluid pressure is applied to the piron rod. Therefore, as compared with the conventional fluid cylinder having the same inner diameter, the output of a plurality of cylinder chambers, that is, a multiple corresponding to the number of pistons can be obtained.

When the pressure fluid is supplied from the second fluid supply passage to the rear side of the piston in the first cylinder chamber through the second pressure fluid supply pipe, the piston rod is pushed back to its original position. The return process is performed. In this case, since the pressure fluid is supplied only to the first cylinder chamber and the discharge amount (fluid supply flow rate) of the pump of the pressure fluid supply system is almost the same as in the pressurization stroke, the return speed of the piston is A speed higher than a multiple value corresponding to the number of a plurality of cylinder chambers is obtained from the piston moving speed in the output stroke, and a quick return effect is obtained.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a fluid cylinder of the present invention will be described with reference to the drawings. Referring to FIG. 1 showing a first embodiment of a fluid cylinder according to the present invention, a cylinder unit 100
Is formed by fitting a first cylinder body 101 having a first cylinder chamber 131 and a second cylinder body 102 having a second cylinder chamber 132 on both sides of a partition member 103. 2 in the axial direction by 103
It is divided into two cylinder chambers. Cylinder unit 1
00 to the first cylinder cover 111 and the other end to the second cylinder cover 112, and the cylinder unit 1 with bolts 116 penetrating these cylinder covers.
It is fixed so as to sandwich 00.

A seal 117 is provided at the fitting portion between the first cylinder cover 111 and the first cylinder body 101, and a fitting portion between the first cylinder body 101 and the second cylinder body 102 and the partition member 103, respectively. The seal 118 is arranged and in a liquid-tight state. Through holes are provided in the partition member 103 and the second cylinder cover 112, respectively, and the piston rod 200 is slidably supported through these through holes. A seal 120 is arranged in the through hole of the partition member 103 to be in a liquid-tight state.

The first piston 113 is housed in the first cylinder chamber 131, and the second piston 114 is housed in the second cylinder chamber 132, and they are fixed to the piston rod 200, respectively. These pistons are the piston rod 2
It is slidable in the cylinder chambers 131 and 132 integrally with 00. Piston 113 and piston ring 1
41, a piston 114 is provided with a piston ring 142, which maintains liquid-tight contact with the inner walls of the cylinder bodies 101 and 102, respectively. The first piston 113 has a pressure surface A1 and a back surface B1, and the second piston 114 has a pressure surface A2 and a back surface B2.

The pressing surface A1 of the first piston 113 in the first cylinder chamber 131 is attached to the first cylinder cover 111.
There is provided a first flow hole 121 for communicating the side with the first pressure fluid supply pipe 502 of the hydraulic device 500 as the pressure fluid supply system.
B1 of the first piston 113 of the cylinder chamber 131 of the
Side and the second pressure fluid supply pipe 50 of the hydraulic device 500.
The 2nd circulation hole 122 which connects 3 and 3 is provided. Further, the piston rod 200 communicates with the pressurizing surface A1 side of the first piston 113 and the hole 212 provided in the upper portion of the second piston 114 on the pressurizing surface A2 side.
11 is provided. As a result, the first piston 113 in the first cylinder chamber 131 and the second piston
Surface A of the second piston 114 of the cylinder chamber 132 of
The 2 side is always in communication. Thus, the first circulation hole 121 and the communication hole 211 constitute a first fluid supply path for allowing the pressure fluid to flow in and out from the pressure surface side of each piston of the first and second cylinder chambers 131 and 132, By the second circulation hole 122, the first cylinder chamber 1
A second fluid supply path for allowing the pressure fluid to flow in and out of the back surface B2 side of the piston 113 of 31 is configured.

The second cylinder cover 112 is provided with a vent hole 133 for communicating the rear surface B2 side of the second piston 114 of the second cylinder chamber 132 and the outside of the cylinder unit 100.

The first piston 113 is fitted so as to engage with a step formed on the upper end of the piston rod 200, and is fixed with a nut 115. The second piston 114 is fitted so as to engage with a step formed at a predetermined distance from the upper end of the piston rod 200,
The upper surface portion is brought into contact with the clip 143 to be locked. This is because in the first piston 113, the fluid pressure alternately acts on the pressurizing surface A1 side and the back surface B1 side.
While it is necessary to firmly fix the piston 113 of the second piston 114 to the piston rod in both directions of the output stroke and the return stroke, in the second piston 114, the fluid pressure acts on the pressurizing surface A2 in the output stroke. Since the back surface B2 of the second piston 114 may be subjected to fluid pressure by simply doing so, it is sufficient to firmly fix the second piston 114 to the piston rod 200 in the direction of the output stroke. The B2 side is received by the step formed on the piston part 200, and the pressing surface A2 side is locked by the locking clip 143.

The second cylinder cover 112 serves as a rotation stopping means for the piston rod 200, if necessary.
An anti-rotation member 232 is provided, which is used as the piston rod 20.
It can be slidably brought into contact with the flat surface portion 201 formed on the side surface of No. 0. The details are shown in FIG. The rotation stopping member 232 is fixed by a screw 233. Second
Since the fluid pressure does not act on the cylinder cover 112, it is not necessary to provide a seal. In the conventional fluid cylinder, there is a problem that the pressure fluid leaks when the detent is provided on the cylinder cover. Even if the stop is provided, the pressure fluid does not leak.

Further, if necessary, the piston rod 2
00, the auxiliary rod 231 is attached to the lower end portion of the second piston 114 of the second cylinder chamber 132 in parallel with the piston rod 200 and through the ventilation hole 133 of the second cylinder cover 112. The auxiliary rod 231 is extended toward the back surface, and the auxiliary rod 231 is provided with upper and lower limit switches R1 and R2 for the moving distance of the piston rod 200.
It is possible to attach a dog D for operating the.

Next, the operation of the fluid cylinder of the first embodiment described above will be described. As shown in FIG. 1, the hydraulic device 500
The oil liquid in the oil tank 504 is
The pressure fluid is supplied to the first circulation hole 121 through the first pressure fluid supply pipe 502 via the switching valve 501. The pressure fluid flows into the pressurizing surface A1 side of the first piston 113 of the first cylinder chamber 131, and further, from the inlet 210 of the communication hole 211 of the piston rod 200 to the communication hole 2.
11 through the hole 212 on the pressurizing surface A2 side of the second piston 114 to the second piston 1 of the second cylinder chamber 132.
It flows into the pressing surface A2 side of 14.

The first piston 113 and the second piston 1
14 is the output of the piston rod 200 multiplied by the pressure of the oil liquid to the area obtained by adding the area of the pressing surface A1 of the first piston 113 to the area of the pressing surface A2 of the second piston 114 when pressed by the hydraulic pressure. And perform the output process. At the same time, the oil liquid on the rear surface B1 side of the first piston 113 in the first cylinder chamber 131 is discharged into the second circulation hole 122 and the second circulation hole 122.
The pressure fluid supply pipe 503 and the switching valve 501 are returned to the oil tank.

When the output stroke is completed, the pump 505 is stopped by the control device (not shown), and the supply of the pressure fluid is stopped.

Next, when the pump 505 is re-driven by the control device (not shown) and the switching valve 501 is operated as shown in FIG. 2, the pressure fluid is, contrary to the above, the second fluid pressure supply pipe. 503 from the first through the second circulation hole 122
B1 of the first piston 113 of the cylinder chamber 131 of the
Supplied to the side, the first piston 113 is pushed in the opposite direction, and the piston rod 200 performs the return stroke. At this time, the second piston 114 in the second cylinder chamber 132
The oil liquid on the pressurizing surface A2 side of the first cylinder chamber 131 is pushed back to the pressurizing surface A1 side of the first piston 113 of the first cylinder chamber 131 through the hole 212 and the communication hole 211. It merges with the oil liquid on the pressurizing surface A1 side of the piston 113 to form the first flow hole 121 and the first pressure fluid supply pipe 50.
2 and the switching valve 501, and is returned to the oil tank 504. Then, when the return stroke is completed, the pump 505 is stopped by the control device (not shown), and the supply of the pressure fluid is stopped.

Next, a second embodiment of the present invention will be described with reference to FIG. The cylinder unit 100 includes a first cylinder body 101 having a first cylinder chamber 131 and a second cylinder body 11 having a second cylinder chamber 132.
4 is fitted to both sides of the first partition member 103, and the third cylinder body 104 having the third cylinder chamber 152 is attached to the second cylinder body 102 via the second partition member 105. It is formed by being connected, and is partitioned into three cylinder chambers in the axial direction by two partition members 103 and 105. A first cylinder cover 111 is fixed to one end of the cylinder unit 100, and a second cylinder cover 112 is fixed to the other end of the cylinder unit 100 via bolts 116 so as to sandwich the cylinder unit 100.

A hole is provided in the second partition member 105, and the piston rod 200 is slidably and liquid-tightly passed therethrough. Then, in the third cylinder chamber 152, the third piston 151 having the pressing surface A3 and the back surface B3 is
It is slidably and liquid-tightly accommodated in the inner wall of the third cylinder body 104. Like the second piston 114, the third piston 151 is fixed to a predetermined position of the piston rod 200 and locked by a locking clip 144.

The piston rod 200 has an inlet 21 at the upper end.
From 0, the hole 21 on the pressure surface A2 side of the second piston 114
2 and a hole 213 on the pressurizing surface A3 side of the third piston 151.
A communication hole 211 communicating with and is provided, and by this,
The pressurizing surface A1 side of the first piston 113 of the first cylinder chamber 131, the pressurizing surface A1 side of the second piston 114 of the second cylinder chamber 132, and the third piston 151 of the third cylinder chamber 152. Is always in communication with the pressure surface A3 side of
The first fluid supply path is constituted by this and the circulation hole 121 of the first cylinder cover 111.

The second partition member 105 is provided with a vent hole 123 for communicating the rear surface B2 side of the second piston 114 of the second cylinder chamber 132 with the outside of the cylinder unit 100, and the second cylinder cover 112 is As in the first embodiment, there is a ventilation hole 133 that connects the back surface B3 side of the third piston 151 of the third cylinder chamber 152 to the outside of the cylinder unit 100.

In FIG. 4, seals 128 and 129 are provided on the second partition member 105, and the piston ring 14
5 is attached to the third piston 151. The other configurations are the same as those in the first embodiment, and therefore their explanations are omitted.

Next, the operation of the fluid cylinder of the second embodiment will be described. When the oil liquid from the hydraulic device 500 is supplied to the first circulation hole 121 of the first cylinder cover 111, the oil liquid becomes the first piston 1 of the first cylinder chamber 131.
13 to the pressurizing surface A1 side, and further to the piston 200
Through the communication hole 211 of the second cylinder chamber 132 into the pressurizing surface A2 side of the second piston 114 of the second cylinder chamber 132, and further from the hole 213 of the third piston 151 of the third cylinder chamber 152. It flows into the pressure surface A3 side and pushes the three pistons 113, 114, 151. At this time, the first, second and third pistons 1 are attached to the piston rod 200.
The combined output of the forces acting on 13, 114 and 151 is given, and the piston rod 200 performs the output stroke.

During the return stroke, the first cylinder chamber 131
The oil liquid is supplied only to the back surface B1 side of the first piston 113 of the first cylinder 113, and the second piston of the second cylinder chamber 132 and the pressurizing surface A1 side of the first piston 113 of the first cylinder chamber 131 in the output stroke. The oil liquid that has entered the pressurizing surface A2 side of 114 and the pressurizing surface A3 side of the third piston 151 of the third cylinder chamber 152 follows the original route to the hydraulic device 5
00 oil tank 504.

In the second embodiment, the piston rod 200
In comparison with the conventional fluid cylinder having the same cylinder inner diameter, the output can be nearly tripled. Then, the return stroke is performed at least three times as fast as the output stroke.

Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, in the fluid cylinder of the second embodiment (FIG. 4), the first partition member 103 is connected to the third cylinder chamber 132 which is in communication with the second piston 114 on the pressurizing surface A2 side. A pipe 508 having a through hole 321 provided outside the cylinder unit 100.
Through the first circulation hole 121 of the first cylinder cover 111, and further to the second partition member 105, the fourth partition member 105, which communicates with the pressurizing surface A3 side of the third piston 151 of the third cylinder chamber 152. A through hole 313 is provided, and the first through hole 121 and the third through hole 32 are provided through a pipe 507 and a pipe 508 provided outside the cylinder unit 100.
1 and the communication hole 211 of the second embodiment.
The first fluid supply path is formed except for the holes 212 and 213.

The other structure of the third embodiment is the same as that of the second embodiment, and the description thereof is omitted. Also, the third
The operation of the fluid cylinder according to this embodiment is the same as that of the second embodiment.

In the three embodiments described above, the example in which the cylinder chamber is divided into two or three is given, but it is also possible to have four or more cylinder chambers. Further, in the above-described embodiment, the cylinder chamber adjacent to the first cylinder cover is referred to as the first cylinder chamber, and the second fluid supply passage is provided on the back side of the first piston.
When there are two or more cylinder chambers, any cylinder chamber other than the cylinder chamber adjacent to the second cylinder cover can be used as the first cylinder chamber. That is, in the output stroke, the fluid pressure acts on the piston in each cylinder chamber, and in the return stroke, the pressure fluid may be supplied to the back side of the piston in only one cylinder chamber of the plurality of cylinder chambers.

[0035]

In the fluid cylinder according to the present invention, the pistons housed in each of the plurality of cylinder chambers are fixed to one piston rod, and the output obtained by adding the forces acting on the plurality of pistons is applied to the piston rod. Since it was given, compared to the conventional fluid cylinder of the same cylinder inner diameter,
A multiple value output corresponding to the number of cylinder chambers can be obtained. Further, since the pressure fluid is supplied to the back surface of only one of the cylinder chambers of the plurality of cylinder chambers to return the piston, the return stroke is faster than the output stroke.

Further, since at least one cylinder chamber of the plurality of cylinder chambers is not supplied with the pressure fluid to the rear face side of the piston, the piston rod is attached to the member facing the rear face of the piston of the cylinder chamber. There is also an advantage that a rotation preventing means can be provided and a rod member having a dog for activating a limit switch can be extended on the back side of the piston in the cylinder chamber.

Further, it is possible to use a compressed air device as the pressure fluid supply system instead of the hydraulic device.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a first embodiment of a fluid cylinder according to the present invention, schematically showing a pressure fluid supply system.

FIG. 2 is a schematic diagram of a pressure fluid supply system when a fluid cylinder is caused to perform a return stroke.

FIG. 3 is a cross-sectional view taken along line XX of FIG.

FIG. 4 is a longitudinal sectional view of a second embodiment of the fluid cylinder according to the present invention, schematically showing a pressure fluid supply system.

FIG. 5 is a longitudinal sectional view of a third embodiment of the fluid cylinder according to the present invention, schematically showing a pressure fluid supply system.

FIG. 6 is a vertical sectional view showing a conventional fluid cylinder.

FIG. 7 is a vertical cross-sectional view showing another conventional fluid cylinder.

[Explanation of symbols]

 100 Cylinder Unit 101 First Cylinder Body 102 Second Cylinder Body 103 First Partition Member 104 Third Cylinder Body 105 Second Partition Member 111 First Cylinder Cover 112 Second Cylinder Cover 113 First Piston 114 Second Piston 131 First Cylinder Chamber 132 Second Cylinder Chamber 151 Third Piston 152 Third Cylinder Chamber 200 Piston Rod 232 Piston Rod Detent Member 500 Pressure Fluid Supply System

Claims (9)

[Claims] 1. A cylinder unit partitioned into a plurality of cylinder chambers in the axial direction by a partition member, and a first cylinder cover fixed to one end of the cylinder unit,
A second cylinder cover fixed to the other end of the cylinder unit, a piston rod slidably supported by penetrating the partition member and the second cylinder cover, and each cylinder of the plurality of cylinder chambers. A piston that is liquid-tightly and slidably accommodated in a chamber, has a pressure surface and a back surface, and is fixed to the piston rod,
A first fluid supply path for letting the pressure fluid flow in and out of the pressure surface of the piston of each of the cylinder chambers, and a pressure fluid flowing in and out of the back side of the piston of the first cylinder chamber of the plurality of cylinder chambers. A fluid cylinder provided with a second fluid supply path for allowing the fluid to flow, and a vent hole for communicating the back side of the piston of each cylinder chamber other than the first cylinder chamber with the outside of the cylinder unit. 2. The first fluid supply path is provided on the piston pressurizing surface side of the first cylinder chamber, and the first pressure fluid supply pipe and the piston pressurizing surface side of the first cylinder chamber are provided. And a communication hole that is provided in the piston rod and that communicates the pressurizing surface sides of the pistons of the plurality of cylinder chambers with each other, and the second fluid supply path includes the first fluid flow path. 2. The fluid cylinder according to claim 1, comprising a second circulation hole that connects the back side of the piston of the cylinder chamber of the second chamber and the second pressure fluid supply pipe. 3. The first fluid supply passage is provided on the pressurizing surface side of the piston of the first cylinder chamber, and connects the first pressure fluid supply pipe and the pressurizing surface side of the first cylinder chamber. And a pipe that is provided outside the cylinder unit and that communicates the pressurizing surface side of the pistons of the plurality of cylinder chambers, and the second fluid supply path is the first cylinder. The fluid cylinder according to claim 1, wherein the fluid cylinder comprises a second communication hole that connects the back side of the piston of the chamber and the second pressure fluid supply pipe. 4. The first cylinder cover is fixed to one end of the first cylinder chamber on the pressurizing surface side of a piston housed in the cylinder chamber, and the first cylinder cover is fixed to the one end. Fluid cylinder. 5. The fluid cylinder according to claim 4, wherein the first circulation hole is provided in the first cylinder cover. 6. The fluid cylinder according to claim 5, wherein the second circulation hole is provided in a partition member on the rear surface side of the piston in the first cylinder chamber. 7. The fluid cylinder according to claim 4, wherein the piston rod is provided with a rotation stopping means. 8. The rotation preventing means is provided on a flat surface portion formed on a side surface of the piston rod and on the second cylinder cover, and the rotation stopping means slidably abuts on the flat surface portion of the piston rod. The fluid cylinder according to claim 7, comprising a stop member. 9. An auxiliary rod is attached to a portion of the piston rod projecting from the second cylinder cover in parallel with the piston rod, and the ventilation hole is provided in the second cylinder cover. 8. A dog for enabling the second cylinder cover to be fixed in and out of the cylinder chamber through which the second cylinder cover is fixed, and attaching a dog for operating the upper limit switch and the lower limit switch to the auxiliary rod. The fluid cylinder described.