JP2000283117A - Hydraulic cylinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve strength in a piston fastening part with a simple structure without using a special high-strength material for a piston rod of a hydraulic cylinder or applying heat treatment to the piston rod. SOLUTION: In this cylinder, the front end of a piston rod 3 is formed with a male thread part 3d, while a piston 4 has a recess with a bottom formed with a female thread part capable of meshing with the male part 3d of the piston rod 3. A bottom part of the recess is formed with six threaded through- holes open to the recess. After insertion of an insertion part 3c through a cushion ring 30, the female thread part of the recess of the piston 4 is screwed on the male thread part 3d of the piston rod 3 until an end face of the piston rod 3 comes into contact with the bottom part of the recess of the piston 4. In this state, by screwing bolts 22 in the threaded through-holes until the front ends of the bolts 22 abut on the end face of the piston rod 3 and by fastening each the bolt 22 to a specified torque, the piston 4 is fastened to the piston rod 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic cylinder, and more particularly to a hydraulic cylinder having an improved piston fastening structure in a hydraulic cylinder used for a hydraulic working machine such as a hydraulic shovel.

[0002]

2. Description of the Related Art In a hydraulic working machine represented by a hydraulic shovel, a hydraulic cylinder is used as an actuator for driving a working member. As shown in FIG. 7, the hydraulic cylinder includes a cylinder body 102, a piston rod 103 moving in the cylinder body 102,
A piston 104 is provided at the tip of the piston rod 103 and partitions the inside of the cylinder body 102 into a rod side chamber 107a and a bottom side chamber 107b. As a piston fastening structure of such a hydraulic cylinder, generally, a small-diameter piston insertion portion 103f is provided at a tip portion of a piston rod 103 via a step portion 103e, and a male screw portion 10 is provided at a tip portion of the piston insertion portion 103f.
3 g, and the piston 104 is
The piston 104 is fixed to the piston rod 103 by tightening the nut 112 into the male screw portion 103g so that the piston 104 comes into contact with the step portion 103e.

[0003] Such a piston fastening structure is disclosed, for example, in Japanese Utility Model Publication No. Hei 7-16888.

FIG. 8 shows another example of a conventional piston fastening structure. This example is disclosed in Japanese Utility Model Laid-Open Publication No. 57-203103.
With the piston 104 fitted to the step 103m until it abuts, a circular ring is radially inserted into the annular groove 103k in the radial direction.
The divided half-ring-shaped flange 160 is fitted, and the flange 160 is fixed to the piston 104 with bolts 170 to fix the piston 104, and the piston rod 1
03. In this case, the chamber 107 in the cylinder body 102 separated by the piston 104
a piston insertion portion 103j for sealing between a and 107b
An O-ring 180 is provided between the piston and the piston 104.

On the other hand, the hydraulic cylinder is provided with a cushion device for reducing an impact at the stroke end of the piston rod. FIG. 7 also shows a floating type (floating type) cushion device using a cushion ring.

In FIG. 7, a cushion ring insertion portion 103a is provided between a piston rod 103 and a piston insertion portion 103f. The diameter of the piston rod 103, the cushion ring insertion portion 103a, and the piston insertion portion 103f are reduced in this order. The cushion ring 130 is loosely fitted to the cushion ring insertion portion 103a so as to be movable in the axial direction and the radial direction. A groove 130a is provided at the piston-side end of the cushion ring 130, and the opposite end can be in close contact with a step 103b which is a boundary between the piston rod 103 and the cushion ring insertion portion 103a. When the hydraulic cylinder extends and enters the cushion hole in front of the supply / discharge port near the stroke end, the cushion ring 130 raises cushion pressure in the chamber 107a while performing a centering function with respect to the cushion hole, and reduces the stroke speed. Reduces the impact at the end of the stroke. Also,
When the hydraulic cylinder contracts from its stroke end position, the hydraulic cylinder is pulled out of the cushion hole by the one-way flow path function through which the pressurized oil passes through the groove 130a and operates well.

[0007] Such a floating type cushion device is also disclosed, for example, in the above-mentioned Japanese Utility Model Publication No. 7-16888.

[0008]

[0007] In the hydraulic cylinder shown in FIG.
When the pressure oil is supplied to 7b, the piston rod 103 moves to the left in the drawing to extend the hydraulic cylinder, and when the pressure oil is supplied to the rod side chamber 107a, the piston rod 10
3 moves rightward in the figure, and the hydraulic cylinder contracts. In a hydraulic working machine such as a hydraulic excavator, such a hydraulic cylinder is frequently expanded and contracted, and the pressure of the chamber 107a or 107b acts on the piston 104 each time.

In the conventional piston fastening structure shown in FIG. 7, the piston 104 is connected to the stepped portion 10 as described above.
3e while the nut 112 is in contact with the male screw portion 103g.
Male screw part 1
The principal stress acting on 03 g is tensile stress. When the pressure of the chamber 107a or 107b acts on the piston 104, this pressure is applied to the cross section of the male screw portion 103g on which such tensile stress is acting, and the piston rod 103 is moved from the male screw portion 103g. It was easy to break.

FIG. 9 shows this state. FIG. 9 shows the relationship between the maximum principal stress acting on the male screw portion 103g of the piston insertion portion 103f and the number of screw threads. The number of threads is the load point when the nut 112 is tightened, that is, the piston 104
And the contact surface of the nut 112. Male thread part 10
The tensile stress acting on 3g repeatedly increases and decreases between the time of pressing the bottom side and the time of pressing the bottom side, and the maximum tensile stress is applied to the first thread portion. Occur.

When a cushion device is provided on the piston rod, the male screw portion 103g
The amplitude of the tensile stress acting on
Is more easily damaged.

As described above, in the conventional piston fastening structure shown in FIG. 7, it is easy to break from the male screw portion 103g, and in order to minimize this damage, the piston rod 103 is made of a high-strength material. It was necessary to increase the strength of the first thread portion of the male screw portion 103g by performing heat treatment or the like.

Further, in the conventional piston fastening structure shown in FIG. 8, the pressure applied to the piston 104 is received at the cross section of the annular groove 103k of the piston insertion portion 103j, and it is easy to break from this portion, as shown in FIG. Similarly, the strength of the piston rod 103 needs to be increased. Further, in this structure, two half ring-shaped flanges 160 are required, and an O-ring is provided between the piston insertion portion 103j and the piston 104 to seal between the two chambers 107a and 107b divided by the piston 104. 180
And the number of parts increases.

An object of the present invention is to provide a hydraulic cylinder capable of improving the strength of a piston fastening portion with a simple structure without using a special high-strength material for a piston rod or performing heat treatment.

[0015]

(1) In order to achieve the above object, according to the present invention, a piston is fastened to the tip of a piston rod, and the piston is used to move the inside of a cylinder body into a rod-side chamber and a bottom-side chamber. A male thread portion is provided at the tip of the piston rod, a bottomed recess having a female thread portion with which the male thread portion can be engaged is formed in the piston, and the piston has a recess. A threaded through-hole opening into the recess is formed at the bottom of the piston, and a female thread of the bottomed recess of the piston is screwed into a male thread at the tip of the piston rod to form a threaded through-hole formed in the piston. A bolt is screwed into the hole until the tip of the bolt contacts the end face of the piston rod, and the piston is fixed to the piston rod by tightening the bolt. That.

By fixing the piston to the piston rod by tightening with a bolt as described above, 1) the external thread portion of the piston rod and the external thread portion of the bolt receive a compressive stress unlike the conventional case; Because the load point is different from the load point when applying hydraulic pressure, both the piston rod and bolt
When the bolts are tightened, a stress having a small amplitude acts on the threads of the male thread portion on the side where the load is shared largely; when hydraulic pressure is applied; 3) The hydraulic pressure and impact from the rod side are mainly caused by the male force of the piston rod. The role of each screw portion is shared such that the oil pressure and impact from the bottom side are received mainly by bolts.

The stress amplitude of each male screw portion is smaller than in the above 2) and 3), and together with 1), the impact resistance of the piston rod and the bolt is improved. Therefore, the strength of the piston fastening portion can be improved with a simple structure without using a special high-strength material for the piston rod or performing heat treatment, and the life can be extended.

(2) In the above (1), preferably,
In a portion of the piston rod adjacent to the piston,
A floating type cushion ring which can be moved in the radial direction and the axial direction is loosely fitted to reduce the impact at the stroke end of the piston rod.

As a result, a cushion effect is obtained, and even in a hydraulic cylinder having such a cushion ring, the impact resistance of the piston rod and the bolt is improved as compared with the above 1), 2) and 3). Long life can be achieved.

(3) In order to achieve the above object,
The present invention fastens the piston to the tip of the piston rod,
In a hydraulic cylinder that separates the inside of the cylinder body into a chamber on the rod side and a chamber on the bottom side with this piston,
A male screw portion is provided at the tip of the piston rod, and a bottomed recess having a female screw portion with which the male screw portion can be engaged is formed on the piston. It is assumed that the piston is fixed to the piston rod by screwing it into the male screw portion at the tip of the rod and tightening it.

By tightening the piston and fixing the piston to the piston rod in this manner, the above-mentioned 1) can be achieved.
Since the external thread of the piston rod receives compressive stress unlike before, the impact resistance of the piston rod is improved, and a simple structure without using special high-strength material or heat treatment for the piston rod Thus, the strength of the piston fastening portion can be improved, and the life can be extended.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an entire hydraulic cylinder 1 according to an embodiment of the present invention, and FIG. 2 shows an enlarged view of a piston portion.

In FIG. 1, a hydraulic cylinder 1 has a cylinder body 2, a piston rod 3, and a piston 4. The cylinder body 2 has a cylindrical tube 5 closed at one end 5a and open at the other end 5b. Open end 5 of tube 5
and a rod-side cylinder head 6 fixedly attached to the cylinder head b. The piston rod 3 extends into and out of the tube 5 through the rod-side cylinder head 6, and at the tip of the piston rod 3 located in the cylinder body 2,
A piston 4 slidable in the tube 5 and dividing the inside of the cylinder body 2 into a rod-side chamber 7a and a bottom-side chamber 7b is fastened. A seal ring 13, a wear ring 14, and a contamination seal 15 are provided on the outer periphery of the piston 4, as shown in FIG. The rod-side cylinder head 6 is provided with a supply / discharge port 8 for supplying / discharging hydraulic oil to / from the chamber 7a.
Is provided with a supply / discharge port 9 for hydraulic oil to / from the chamber 7b.

The chamber 7b on the bottom side of the supply / discharge port 9
When the supply / discharge port 8 communicating with the rod-side chamber 7a is connected to the tank, the piston 4 slides toward the rod-side cylinder head 6 on the left side in the drawing to displace the piston rod 3 into the cylinder body 3 And the hydraulic cylinder 1 is extended. When pressure oil is supplied to the chamber 7a on the rod side via the supply / discharge port 8 and the supply / discharge port 9 communicating with the chamber 7b on the bottom side is connected to the tank, the piston 4 closes the closed end of the tube 5 on the right side in the figure. Part 5a
The piston cylinder 3 is slid and displaced so as to draw the piston rod 3 into the cylinder body 2, and the hydraulic cylinder 1 contracts. Attachment part 1 provided at tube closed end 5a of cylinder body 2
0 and a mounting portion 11 provided at the outer end of the piston rod 3
By pivotally connecting one to the fixed member and the other to the movable member, the movable member can be driven.

Next, a piston fastening structure and a cushion device which are features of the present invention will be described with reference to FIG.

In FIG. 2, a small diameter portion 3a is provided at the tip of the piston rod 3, and the small diameter portion 3a is separated from the main body of the piston rod 3 by a radial step 3b. The small-diameter portion 3a has a cushion ring insertion portion 3c and a male screw portion 3d, and the rod-side cushion ring 30 is loosely fitted to the cushion ring insertion portion 3c so as to be movable in the axial direction and the radial direction. The piston 4 is screwed and fixed. Also, the cushion ring insertion part 3c
In the portion adjacent to the male screw portion 3d, an R portion 3e serving as a relief portion during polishing of the cushion ring insertion portion 3c is formed. Groove 3 is provided on the piston-side end surface of cushion ring 30.
0a is provided.

The piston 4 has a bottomed recess 4b formed with a female thread 4a capable of engaging with the male thread 3d of the piston rod 3, and the recess 4b is formed in the bottom 4c of the recess 4b.
A plurality of, for example, six, threaded through holes 4d are formed.

A positioning projection 3g is projected from the center of the end face 3f of the male screw portion 3d of the piston rod 3, and a positioning recess 4e into which the projection 3g is fitted is formed at the center of the bottom 4c of the recess 4b of the piston 4. Is formed.

After the cushion ring 30 is inserted into the insertion portion 3c, the piston 4 is inserted into the male screw portion 3d of the piston rod 3.
Screw 4a until the end face 3f of the piston rod 3 comes into contact with the bottom 4c of the recess 4b of the piston 4. In this state, the bolt 22 is inserted into the threaded through hole 4d. The piston 4 is fastened to the piston rod 3 by screwing it into contact with the end face 3f of the piston rod 3 and tightening the bolt 22 to a specified torque.

The state of engagement between the male thread 3d of the piston rod 3 and the internal thread 4a of the piston 4 when the bolt 22 is tightened is shown in the upper left of FIG. Each is shown enlarged in the upper right of FIG. In the latter, 22a is a male screw part 22a of the bolt 22, and 4f is a female screw part of the threaded through hole 4d. By tightening with the bolt 22, both the male screw part 3d of the piston rod 3 and the male screw part 22a of the bolt 22 receive compressive stress unlike the related art.

FIGS. 3 and 4 show the stress distributions of the male screw portion 3d and the male screw portion 22a at the time of tightening the bolts by curves A,
Shown by B. The horizontal axis in FIG. 3 is the number of threads counted from the end surface 4g on the rod side of the piston 4, and the horizontal axis in FIG. 4 is the number of threads counted from the tip of the bolt 22.

At the portion where the external thread 3d of the piston rod 3 meshes with the internal thread 4a of the piston 4, the tightening force on the external thread 3d becomes a compressive stress and the bolt 2
Since the tightening load point 2 is located on the end face 3f of the piston rod 3, the compressive stress increases as the number of threads from the first thread increases, as indicated by A in FIG. Bolt 22
In the engagement portion between the bolt 22 and the threaded through-hole 4d, the tightening force of the bolt 22 with respect to the male screw portion 22a is a compressive stress, and when the tightening load point of the bolt 22 is broken, the bolt 22 is located at the tip of 22. As shown, as the number of threads increases from the first thread, the compressive stress decreases.

Next, when pressure oil is introduced into the chamber 7a or 7b and an oil pressure is applied to the piston 4, the male screw 3
The forces acting on d and 22a will be described. Curve C in FIG. 3 shows the piston rod 3 when hydraulic pressure is applied to the rod side.
FIG. 4 shows a stress distribution in the external thread portion 3d of the bottle 22. The curve D in FIG.
3 shows a stress distribution of a.

When hydraulic pressure is applied from the rod-side chamber 7a: Since the load point of the hydraulic pressure is different from the load point at the time of tightening the bolt 22, it is on the end surface 4g of the piston 4 on the rod side.
The load of the hydraulic pressure is transmitted as a compressive stress σa from the first thread of the male thread portion 3d to the next thread sequentially. In this case, the load of the hydraulic pressure applied from the rod side is shared by the threads on the side (first thread side) that does not share the tightening load during bolt tightening. In other words, the stress σa due to the hydraulic pressure is repeatedly generated every time the hydraulic pressure is applied, but the stress on the side with the large amplitude due to the hydraulic pressure is not shared by the screw thread having the high tightening stress of the bolt 22, and the tightening stress Is shared among the threads that do not share much. In addition, since most of the hydraulic pressure on the rod side is shared by the male screw portion 3d of the piston rod 3, the bolt 22 hardly shares the hydraulic pressure load.

When hydraulic pressure is applied from the bottom side chamber 7b: Unlike the load point at the time of tightening the bolt 22, the hydraulic pressure is placed on the bottom end surface 4h of the piston 4, so that, as described above, The load of the hydraulic pressure is transmitted as a compressive stress σb from the thread of the external thread portion 22a on the end face 4h side of the piston 4 to the adjacent thread in order. Also in this case, the load of the hydraulic pressure is shared by the threads that do not share the load when tightening the bolt. In other words, the stress σ due to the hydraulic pressure
b is repeatedly generated every time the hydraulic pressure is applied, but the stress on the side where the amplitude is large due to the hydraulic pressure is not shared with the screw thread with high tightening stress of the bolt 22, and the screw thread on the side that does not share much the tightening stress. Is shared. In addition, since most of the hydraulic pressure on the bottom side is shared by the male screw portion 22a of the bolt 22, the male screw portion 3 of the piston rod 3 hardly shares the oil pressure load.

To summarize the above, 1) By tightening with the bolt 22, the external thread 3d of the piston rod 3 and the external thread 22a of the bolt 22 receive compressive stress unlike the conventional one.

2) Since the load point at the time of tightening the bolt and the load point at the time of applying the hydraulic pressure are different, both the piston rod 3 and the bolt 22 have the male screw portions 3d and 22a on the side where the load is largely shared at the time of tightening the bolt. The stress on the side with the smaller amplitude acts on the screw thread at the time of hydraulic pressure load.

3) Hydraulic pressure and impact from the rod side are mainly received by the male thread 3d of the piston rod 3, and hydraulic pressure and impact from the bottom side are mainly received by the bolt 22. Roles are shared.

From the above 2) and 3), the respective male screw portions 3d, 22
The stress amplitude of a becomes small, and the impact resistance of the piston rod 3 and the bolt 22 is improved in combination with the above 1). For this reason, the strength of the piston fastening portion can be improved with a simple structure without using a special high-strength material for the piston rod 3 or performing heat treatment, and a long life can be achieved.

Next, the function of the cushion will be described.

When the pressurized oil is introduced into the supply / discharge port 9 on the bottom side when the piston rod 3 is in the state shown in FIG. 1, the piston rod 3 moves to the left in the drawing and the hydraulic cylinder 1
Elongates. When the cushion ring 30 protrudes into the cushion ring fitting portion 6a provided in the rod side cylinder head 6 near the stroke end, the oil passage of the fitting portion 6a is narrowed, a cushion pressure is raised in the chamber 7a, and the piston rod 3 To reduce the impact speed at the stroke end. At this time, the cushion ring 30 is movable in both the radial direction and the axial direction, and the cushion ring 30 is inserted while being aligned following the hole shape of the cushion ring fitting portion 6a. No need to worry about galling (centering function).

The fitting portion 6a of the cushion ring 30
When the cushion ring 30 enters, the cushion pressure is generated in the chamber 7a, and a pressure difference is generated between the side of the cushion ring 30 entering the fitting portion 6a (the supply / discharge port 8 side) and the piston 4 side (the chamber 7a side). Since the ring 30 is pressed against and adheres to the end face of the step portion 3b, the pressure oil in the chamber 7a is applied to the outer peripheral surface of the cushion ring insertion portion 3a and the cushion ring
Does not flow out to the supply / discharge port 8 through the gap between the inner peripheral surface and the inner peripheral surface. Then, after reaching the stroke end, when the piston rod 3 starts to move in the contracting direction (rightward in the figure) and the cushion ring 30 comes out of the fitting portion 6a, the pressure oil from the supply / discharge port 8 is flush with the outer peripheral surface of the cushion ring 30. Fitting part 6a
Flows into the chamber 7a through a gap with the inner peripheral surface of the chamber 7a.
At this time, the cushion ring 30 is pressed against the end face 4g of the piston 4 by hydraulic pressure from the supply / discharge port 8, but since the groove 30a is provided on the piston side end face of the cushion ring 30, the pressure oil is supplied to the cushion ring insertion portion. 3a
Flows into the chamber 7a through the groove 30a from the gap between the outer peripheral surface of the cushion ring 30 and the inner peripheral surface of the cushion ring 30, and is well extracted and operated (one-way flow path function).

As described above, when the cushioning action is obtained by raising the cushion pressure in the chambers 7a and 7b, the oil pressure becomes considerably high, and the male screw portions 3d and 22 due to the oil pressure are increased.
Although the amplitude of the stress acting on a also increases, according to the present embodiment, even in such a case, the impact resistance of the piston rod 3 and the bolt 22 is improved as compared with the above 1), 2), and 3),
Long life can be achieved.

According to the present embodiment configured as described above, the following effects can be obtained.

(1) In the piston fastening structure of the present embodiment, the external thread 3d of the piston rod 3 and the external thread 22a of the bolt 22 receive compressive stress from the above 1), 2) and 3), and Since the stress amplitude at the threaded portions 3d and 22a is reduced, the impact resistance of the piston rod 3 and the bolt 22 is improved, and the material of the piston 4 can be easily made strong. And the life of the piston rod 3 is improved.

(2) Since the external thread 3d of the piston rod 3 receives a compressive stress and the stress amplitude at the external thread 3d becomes small, it is not necessary to use a high-strength material for the piston rod 3, and the strength is increased by heat treatment. Is no longer necessary,
The piston rod 3 can be made inexpensively with low cost materials.

(3) A small-diameter piston insertion portion which is required in the conventional piston rod becomes unnecessary, and only the insertion portion 3c of the cushion ring 30 on the rod side needs to be provided in the piston rod 1. There is no need to make a step, and the problem of breakage at the step is reduced.

(4) The total length of the piston rod 3 is the bolt 2
The effective stroke of the hydraulic cylinder can be made longer than that of a conventional case using a large nut.

(5) Since a plurality of bolts 22 are used, the tightening torque of each bolt can be reduced, and
Easy disassembly.

A second embodiment of the present invention will be described with reference to FIG. In the figure, the same components as those shown in FIG. 2 are denoted by the same reference numerals.

In FIG. 5, the piston 4A of the hydraulic cylinder according to the present embodiment has a bottomed recess 4b having a female thread 4a capable of engaging with the male thread 3d of the piston rod 3.
This is the same as in the first embodiment.
However, in contrast to the first embodiment in which a plurality of threaded through holes 4d are formed in the bottom 4c of the recess 4b, in the present embodiment, a single large diameter threaded through hole 4Ad is formed. One large-diameter male screw portion 22Aa is inserted into the threaded through hole 4Ad.
The piston 4 is fastened to the piston rod 3 by screwing a bolt 22A having the following shape into contact with the end face 3f of the piston rod 3 and tightening the bolt 22A to a specified torque.

According to the present embodiment, the effects of 1) to 3) are obtained, and the same effects as those of the first embodiment are obtained except for the above (5).

A third embodiment of the present invention will be described with reference to FIG. In the figure, the same components as those shown in FIG. 2 are denoted by the same reference numerals.

In FIG. 6, a piston 4B of the hydraulic cylinder according to the present embodiment has a bottomed recess 4b having a female screw portion 4a capable of engaging with the male screw portion 3d of the piston rod 3.
This is the same as in the first embodiment.
However, in the first embodiment, a plurality of threaded through holes 4d are formed in the bottom 4c of the recess 4b, whereas in the present embodiment, the bottom 4Bc is not provided with a threaded through hole. Instead, the bottom 4Bc is a non-porous flat surface. A hexagonal head 4Bj is formed on the opposite side of the recess 4b of the piston 4B.

After the cushion ring 30 is inserted into the insertion portion 3c, the piston 4 is inserted into the male screw portion 3d of the piston rod 3.
The female screw portion 4a of the recess 4b is screwed using the hexagonal head 4Bj until the end face 3f of the piston rod 3 contacts the bottom 4Bc of the recess 4b of the piston 4, and the piston 4B is tightened to a specified torque. The piston 4 is fastened to the piston rod 3.

Also in this embodiment, by tightening the piston 4B, the external thread 3d of the piston rod 3 is formed.
Receives a compressive stress unlike conventional ones, the impact resistance of the piston rod 3 is improved, and the strength of the piston fastening part can be reduced with a simple structure without using a special high-strength material or heat treatment for the piston rod 3. Can be improved and the service life can be extended.

[0058]

According to the present invention, the following effects can be obtained.

(1) Since the external thread of the piston rod and the external thread of the bolt receive compressive stress and the amplitude of the stress at each external thread is reduced, the impact resistance of the piston rod and the bolt is improved. Since it is easy to make the material of the piston strong, the strength of the piston fastening portion is improved, and the life of the piston rod is improved.

(2) Since the external thread of the piston rod receives compressive stress and the amplitude of the stress at the external thread becomes small,
It is not necessary to use a high-strength material for the piston rod, and it is not necessary to increase the strength by heat treatment.

(3) A small-diameter piston insertion portion, which is required for a conventional piston rod, becomes unnecessary, and even if there is a cushion ring, only the insertion portion of the rod-side cushion ring needs to be provided on the piston rod. It is not necessary to provide an extra step, and the problem of breakage at the step is reduced.

(4) The total length of the piston rod is bolt 22
The effective stroke of the hydraulic cylinder can be increased as compared with the conventional case using a large nut.

[Brief description of the drawings]

FIG. 1 is an overall sectional view of a hydraulic cylinder according to a first embodiment of the present invention.

FIG. 2 is an enlarged detailed sectional view of a piston fastening portion of the hydraulic cylinder shown in FIG.

FIG. 3 is a diagram showing a stress distribution in a male screw portion of a piston rod when a bolt is tightened and when hydraulic pressure is applied from the rod side.

FIG. 4 is a diagram showing a stress distribution of a male screw portion of a bolt when the bolt is tightened and when a hydraulic pressure is applied from the bottom side.

FIG. 5 is an enlarged detailed sectional view of a piston fastening portion of a hydraulic cylinder according to a second embodiment of the present invention.

FIG. 6 is an enlarged detailed sectional view of a piston fastening portion of a hydraulic cylinder according to a third embodiment of the present invention.

FIG. 7 is a sectional view of a piston fastening portion of a conventional hydraulic cylinder.

FIG. 8 is a sectional view of a piston fastening portion of another conventional hydraulic cylinder.

FIG. 9 is a diagram showing a distribution of stress acting on a male screw portion of a piston rod in a conventional hydraulic cylinder.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hydraulic cylinder 2 Cylinder main body 3 Piston rod 3a Small diameter part 3b Step part 3c Cushion ring insertion part 3d Male screw part 3e R part 3f end face 4 Piston 4a Female screw part 4b Recess 3c Bottom part 4d Threaded through hole 4g, 4h Piston end face 4A Piston 4Ad Threaded through hole 4B Piston 4Bc Bottom 4Bj Hexagonal head 5 Tube 6 Rod side cylinder head 7a, 7b Chamber 8,9 Supply / discharge port 22 Bolt 22a Male thread 22A Bolt 22Aa Male thread 30 Rod side cushion ring 30a groove

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Mitsuhiro Yoshimoto 650, Kandamachi, Tsuchiura-shi, Ibaraki F-term in Tsuchiura Plant of Hitachi Construction Machinery Co., Ltd. 3H081 AA02 BB02 CC15 CC24 DD16 EE27 FF19 FF34 HH01 3J069 AA08 CC11 CC13 CC15 DD39

Claims (3)

[Claims] 1. A hydraulic cylinder in which a piston is fastened to a tip of a piston rod and the inside of a cylinder body is divided into a chamber on a rod side and a chamber on a bottom side by the piston, a male thread portion is provided at a tip of the piston rod, The piston is formed with a bottomed recess having a female screw portion with which the male screw portion can be engaged, and a threaded through-hole opening into the recess is formed at the bottom of the recess of the piston. The female screw part of the bottomed recess is screwed into the male screw part at the tip of the piston rod, and a bolt is inserted into a threaded through hole formed in the piston until the tip of the bolt contacts the end face of the piston rod. A hydraulic cylinder wherein the piston is fixed to the piston rod by screwing in and tightening the bolt. 2. A hydraulic cylinder according to claim 1, wherein a floating type cushion ring movable in a radial direction and an axial direction is loosely fitted to a portion of said piston rod adjacent to said piston, and said piston rod has a stroke. A hydraulic cylinder characterized by reducing the impact at the end. 3. A hydraulic cylinder in which a piston is fastened to a tip of a piston rod and the inside of the cylinder body is divided into a rod-side chamber and a bottom-side chamber by the piston. Forming a bottomed recess having a female screw portion with which the male screw portion can mesh with the piston, and screwing and tightening the female screw portion of the bottomed recess of the piston into the male screw portion at the tip of the piston rod. A hydraulic cylinder wherein the piston is fixed to the piston rod by means of