JP2001153108A - Hydraulic cylinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To promote the strength of a piston engaging portion through simple structure without using special high-strength material or heat treatment for a piston rod in a hydraulic cylinder. SOLUTION: A recess 21 is formed as an axial directional insertion part on an end surface 20 on the piston rod 3 side of a piston 4, and the tip of the rod 3 is inserted into the recess 21 of the piston 4 to ensure a coaxial property. Coaxial bolt screw and bolt through holes 24 and 25 are opened on the end surface 23 of the tip of the rod 3 and the piston 4 respectively, to fix the piston 4 by inserting a bolt 22 into the hole 24 from the hole 25, in a condition where the surface 20 of the piston 4 is oppositely contacted to the surface 23 of the tip of the rod 3. An O-ring 51 is provided between the inner peripheral surface of the recess 21 and the rod outer peripheral surface, to inhibit the infiltration of pressure oil in a chamber 7a on the rod side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hydraulic cylinder, and more particularly to a hydraulic cylinder used for a hydraulic working machine such as a hydraulic construction machine.

[0002]

2. Description of the Related Art In a hydraulic working machine such as a hydraulic shovel, which is a typical example of a hydraulic construction machine, a hydraulic cylinder is used as an actuator for driving a working member. As shown in FIG. 14, the hydraulic cylinder is provided at a cylinder main body 102, a piston rod 103 moving within the cylinder main body 102, and a distal end of the piston rod 103, and the inside of the cylinder main body 102 has a rod side chamber 1.
07a and a piston 104 partitioned into a bottom chamber 107b. As such a piston fastening structure of a hydraulic cylinder, a piston rod 103 is generally used.
A small-diameter piston insertion portion 103j is provided at the front end portion of the piston through a step portion 103m, a male screw portion 103g is formed at the front end portion of the piston insertion portion 103j, and the piston 104 is inserted into the piston insertion portion 103j. Nut 112 into the male screw portion 103 so as to abut against the portion 103m.
g, the piston 104 is fixed and fastened to the piston rod 103.

[0003] Such a piston fastening structure is disclosed, for example, in Japanese Utility Model Publication No. Hei 7-16888. FIG. 15 shows another example of the conventional piston fastening structure. This example is disclosed in Japanese Utility Model Laid-Open No. 57-203103, in which a piston insertion portion 103 for inserting a piston 104 is provided.
j is further provided with an annular groove 103k, and the piston 104 is fitted to the step 103m until the annular groove 103k is brought into contact with the step 103m.
3k is fitted with a half-ring-shaped flange 160 obtained by dividing a circular ring into two in the radial direction, and this flange 160 is fixed to the piston 104 with bolts 170, so that the piston 1
04 is fixed and fastened to the piston rod 103.
In this case, an O-ring 180 is provided between the piston insertion portion 103j and the piston 104 to seal the space between the chambers 107a and 107b in the cylinder body 102 separated by the piston 104.

[0004]

In the hydraulic cylinder shown in FIG. 14, when pressure oil is supplied to the bottom chamber 107b, the piston rod 103 moves to the left in the drawing to extend the hydraulic cylinder. Side chamber 107
When the pressure oil is supplied to a, the piston rod 103 moves to the right in the figure and the hydraulic cylinder contracts. In a hydraulic working machine such as a hydraulic excavator, such a hydraulic cylinder frequently expands and contracts.
The pressure of a or 107b acts.

By the way, in the conventional piston fastening structure shown in FIG. 14, when the pressure of the chamber 107a or 107b acts on the piston 104, the piston 104 closes the nut 112 with the male screw portion 103g provided on the piston insertion portion 103j. The pressure in the chamber 107a or 107b is
The piston rod 103 was more likely to be damaged than the male screw portion 103g.

FIG. 16 shows the relationship between the maximum principal stress acting on the male screw portion 103g of the piston insertion portion 103j and the number of screw threads. Here, the number of threads is counted from the load point when the nut 112 is tightened, that is, from the contact surface between the piston 104 and the nut 112. As can be seen from this figure, the maximum tensile stress is applied to the first thread portion on the external thread portion 103g,
In addition, the tensile stress repeatedly increases and decreases between the time of pressing on the rod side and the time of pressing on the bottom side, and breakage of the male screw portion 103g occurs in the first thread portion. Therefore, it is necessary to increase the strength of the first thread portion of the male screw portion 103g by making the material of the piston rod 103 a high-strength material or performing heat treatment on the male screw portion 103g.

Further, in the conventional piston fastening structure shown in FIG. 15, 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 the portion is easily damaged from this portion, as shown in FIG. Similarly, the strength of the piston rod 103 needs to be increased. Also,
In this structure, two half ring-shaped flanges 160 are required, and there is a problem that the number of parts is increased.

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

[0009]

(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 inside of a cylinder body is divided into a rod-side chamber and a bottom-side chamber. In a hydraulic cylinder, a bolt is inserted into a bolt screw hole provided in the piston rod from a bolt through hole formed in the piston in a state where the end surface of the piston on the rod side is at least partially in face contact with the end surface of the tip of the piston rod. The piston is directly fixed to the piston rod with this bolt, and the pressure oil acting in the chamber on the rod side is applied to the face-to-face contact between the end face of the tip of the piston rod and the end face of the piston on the rod side. It is assumed that a seal portion for suppressing intrusion is provided.

[0010] By directly fixing the piston to the piston rod with a bolt as described above, the force applied to the piston during the operation of the hydraulic cylinder is received by the bolt,
Although a tensile stress acts on the bolt, a normal high-strength bolt can be used as the bolt, and it is easy to make the material stronger, so that sufficient strength against the tensile stress can be obtained. On the bolt screw hole side of the piston rod, the screw portion is a female screw and a compressive stress acts on the screw portion, so that sufficient strength can be obtained with a normal piston rod material. For this reason, 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, so that the piston rod can be made inexpensively with a low-cost material. Further, since the bolt is directly fixed with bolts, the fatigue strength against external force is also improved, the strength of the piston fastening portion is improved with a simple structure, and the life of the piston rod can be improved.

Further, since it is directly fixed with bolts, it can be constructed with a minimum number of parts.

Further, since the conventional small-diameter piston insertion portion is not required, there is no need to provide an extra step on the piston rod, and the problem of breakage at the step is reduced.

The above is the operation based on the configuration of the invention of the prior application proposed by Japanese Patent Application No. 10-149467. The present invention
It is an object of the invention of the prior application to improve the strength of the piston fastening structure and to ensure the effect.

That is, by providing the seal portion for suppressing the pressure oil acting in the chamber on the rod side from entering the face-to-face contact portion between the end face of the tip end of the piston rod and the end face of the piston on the rod side as described above, In the case where separation occurs at the facing contact portion and pressure oil enters, an increase in external force due to hydraulic pressure on the separation surface acting on the bolt is avoided, and a decrease in fastening strength due to breakage or loosening of the bolt is prevented, and the piston The effect of improving the strength of the fastening portion is assured.

(2) In the above (1), preferably,
The piston has a concave portion into which the tip of the piston rod is fitted, and the seal portion is provided at a fitting portion between an inner peripheral surface of the concave portion of the piston and an outer peripheral surface of the piston rod.

Accordingly, it is possible to most effectively prevent the pressure oil from entering the face-to-face contact between the end face of the distal end of the piston rod and the end face of the piston on the rod side.

(3) In the above (1), the seal portion may be provided on an outer peripheral portion of a face-to-face contact portion between an end surface of a tip end of the piston rod and a rod-side end surface of the piston.

As a result, it is impossible to provide a seal portion at the fitting portion between the inner peripheral surface of the piston recess and the outer peripheral surface of the piston rod, or even if it is difficult, it is possible to prevent pressure oil from entering the facing contact portion. Can be kept to a minimum.

(4) In the above (1) to (3), preferably, the seal portion is formed of an O-ring.

[0020] Thereby, a general O-
The seal portion can be formed using a ring.

(5) In the above (1) to (3), the seal portion may be constituted by a contact pressing portion between the piston rod and the piston.

Thus, the seal can be formed without using the O-ring.

[0023]

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

FIG. 1 shows a piston fastening structure of a hydraulic cylinder according to a first embodiment of the present invention. The hydraulic cylinder 1 has a cylinder body 2, a piston rod 3, and a piston 4, and the cylinder body 2 It comprises a cylindrical tube 5 having one end 5a closed and the other end 5b open, and a rod-side cylinder head 6 fixed to the open end 5b of the tube 5. The piston rod 3 extends through the rod-side cylinder head 6 into and out of the tube 5. The piston rod 3 is slidable in the tube 5 at the tip of the piston rod 3 located in the cylinder body 2 and inside the cylinder body 2. Is divided into a chamber 7a on the rod side and a chamber 7b on the bottom side.
A seal ring 13, wear rings 14a and 14b, and contamination seals 15a and 15b are provided on the outer periphery of the piston 4. The rod side cylinder head 6 has a chamber 7
A supply / discharge port 8 for hydraulic oil to / from a is provided, and a closed end 5a of the tube 5 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 to move 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, the piston fastening structure which is a feature of the present invention will be described.

End face 2 of piston 4 on piston rod 3 side
0 has a recess 21 as an axial fitting portion,
The piston end face 20 is divided into a bottom face 21a of the recess 21 and an end face portion 20a facing the chamber 7a on the rod side, and the piston 4 is mounted by fitting the tip of the piston rod 3 into the recess 21 so that the piston rod is mounted. 3 and coaxiality. Further, an axial bolt screw hole 24 is formed in the end face 23 of the tip of the piston rod 3, an axial bolt through hole 25 is formed in the recess bottom surface 21 a of the piston 4, and the end face 23 of the tip of the piston rod 3 is formed.
The piston 4 is fixed by inserting and tightening the bolt 22 from the bolt through hole 25 into the bolt screw hole 24 in a state where the concave bottom surface 21 a of the end surface 20 of the piston 4 faces the piston rod 3 and fastened to the piston rod 3. . The number of bolts 22 may be an appropriate number, but in the present embodiment, six bolts 22 are used as shown in FIG. Further, the bolt 22 has been described as an example of a round head bolt, but may be a hexagonal head bolt.

In the piston fastening structure of this embodiment, the piston 4 is directly fastened to the piston rod 3 with the bolts 22, so that the force applied to the piston 4 is reduced by the plurality of bolts 22.
Will receive it. At this time, a tensile stress acts on the bolt 22, but a normal high-strength bolt can be used for the bolt 22, and it is easy to make the material stronger, so that sufficient tensile stress is not applied. Strength is obtained. Also, the bolt screw hole 24 side of the piston rod 3 is
Since the screw portion is a female screw and a compressive stress acts on the screw portion, a sufficient strength can be obtained with a normal piston rod material.

The inner peripheral surface 21 of the recess 21 of the piston 4
b, an O-ring groove 50 is provided, and an O-ring 51 is mounted in the O-ring groove 50. In this state, the piston rod 3
The piston 4 is attached to the fitting portion between the inner peripheral surface 21b of the recess 21 of the piston 4 and the outer peripheral surface of the piston rod 3 so that the distal end surface 23 of the piston rod 3 and the rod-side end surface of the piston 4 are fitted. A seal portion that isolates the facing contact portion 20 (concave end surface 21a) from the rod-side chamber 7a hydraulically so as to prevent pressure oil acting in the rod-side chamber 7a from entering the facing contact portion. Has formed.

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

1) In the conventional general piston fastening structure shown in FIG.
(See FIG. 14).
Since a tensile stress acts on 3 g, a high-strength material must be used for the piston rod. On the other hand, in the piston fastening structure of the present invention, since it is not necessary to provide a male thread portion on the piston rod 3, there is no need to use a high-strength material for the piston rod 3, and it is not necessary to increase the strength by heat treatment, so that the cost is reduced. The piston rod 3 can be made inexpensively with a suitable material.

2) Conventionally, the tensile stress acts on the male screw portion of the piston rod, but in the present invention, it acts on the bolt 22.
Normal high-strength bolts can be used for the bolts 22 and it is easy to make the material stronger,
The strength of the piston fastening portion can be improved with a simple structure, and the life of the piston rod can be significantly improved.

3) By fixing using bolts 22,
Fatigue strength against external force is also improved.

4) In the conventional piston fastening structure shown in FIG. 15, two flanges 160 were required, and the number of parts was large. However, in the present invention, such parts are unnecessary, and the number of parts is small. it can.

5) Since the conventional small-diameter piston insertion portion is not required, the piston rod can be a round bar having no step, and the problem of breakage at the step can be eliminated.

6) The overall length of the rod is determined by the length up to the head of the bolt 22, and the effective stroke of the hydraulic cylinder 1 can be made longer than when a large nut 112 is used as in the conventional case.

7) Since a plurality of bolts 22 are used, the tightening torque of each bolt can be reduced, and assembly and disassembly are easy.

8) Conventionally, the piston rod
In many cases, maintenance is performed by disassembling the piston assembly. For example, when replacing the rod-side cylinder head or replacing the rod seal attached to the cylinder head, remove the nut 112 (see FIG. 14). Each time, the nut had to be put on a special machine to loosen the nut, and the nut had to be loosened using this special machine. The tightening torque of the nut 112 is about 1000
kgfm. In the present invention, the tightening torque of one bolt 22 is as small as about 70 kgfm. For this reason,
The bolt 22 can be loosened by manpower, and the bolt can be loosened without the need for a large-scale dedicated machine, and the serviceability is high.

As described above, according to the present embodiment, 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 4 or performing heat treatment (1) to 5 above. )). Further, the effect of securing the effective stroke length and improving disassembly / assembly and serviceability can be obtained (the above 6) to 8)).

By the way, in the piston fastening structure in which the piston 4 is directly fixed to the piston rod 3 with the bolts 22 as described above, the distal end surface 23 of the piston rod 3 and the rod-side end surface 20 (recess end surface) of the piston 4 during the cylinder operation. 21
If the pressure oil from the rod-side chamber 7a enters the contact portion with the portion a), the expected effect of improving the strength may not be obtained.

FIG. 3 is a view showing the deformation of the piston 4 during the operation of the cylinder which supplies the pressure oil to the rod side chamber 7a and contracts the hydraulic cylinder 1. The hydraulic pressure is applied to the end face 20a of the outer periphery of the piston 4 by an external force. And the outer peripheral portion of the piston 4 is deformed away from the outer peripheral surface of the piston rod 3, and the outer peripheral portion of the facing contact portion between the distal end surface 23 of the piston rod 3 and the end surface 20 (recess end surface 21 a) of the piston 4. Is separated. The separation portion is formed along the bolt 22 as shown in FIG. 4 when viewed from the front. The separation of the facing contact portion also occurs due to factors such as insufficient tightening force of the bolt 22 and insufficient surface accuracy during processing. When the facing contact portion is separated in this way, pressurized oil enters the separated surface from the rod-side chamber 7a, and the oil pressure acts on the bolt 22 as a tensile force. For this reason, in addition to the original hydraulic pressure acting on the piston end surface 20a, the hydraulic pressure acting on the separation surface is applied to the bolt 22, the external force acting on the bolt 22 increases, and the fastening strength due to breakage or loosening of the bolt 22 is increased. May be reduced.

In this embodiment, the front end surface 23 of the piston rod 3 and the end surface 20 of the piston 4 are
A sealing portion that hydraulically isolates the facing portion with the (concave end surface 21a) from the rod-side chamber 7a and suppresses pressure oil acting in the rod-side chamber 7a from entering the facing contact portion is formed. Thus, it is possible to avoid an increase in external force due to the hydraulic pressure of the separating surface acting on the bolt 22, prevent a decrease in the fastening strength due to breakage or loosening of the bolt 22, and improve the strength of the piston fastening portion. You can be sure.

As described above, according to this embodiment, 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 4 or performing heat treatment (1) to 5 above. )), The effect of securing an effective stroke length and improving disassembly / assembly and serviceability can be obtained (the above 6) to 8)), and the pressure oil acting in the rod-side chamber 7a is removed by the piston rod 3 Intrusion into the facing contact portion between the piston and the piston 4 can be suppressed, and the strength of the piston fastening portion can be reliably improved.

Another embodiment of the present invention will be described with reference to FIGS. In the figure, the same parts as those shown in FIG. 1 are denoted by the same reference numerals.

FIG. 5 shows a second embodiment of the present invention, in which a piston 4A is fastened to a piston rod 3A by one bolt 22A. In this case, bolt 2
2A requires a single bolt to apply a large tightening force required for fastening, so it is preferable to use a hexagonal head bolt as shown in the figure.

Also, as in the first embodiment, the piston 4
A seal portion including an O-ring groove 50 and an O-ring 51 is provided at a fitting portion between the inner peripheral surface 21b of the recess 21 of A and the outer peripheral surface of the piston rod 3A, and a pressure acting in the rod-side chamber 7a is provided. The oil is prevented from entering the face-to-face contact portion between the end face 23 of the distal end of the piston rod 3A and the rod-side end face 20 (recess end face 21a) of the piston 4A.

FIG. 6 shows a third embodiment of the present invention, in which a hole 30 for an axial fitting portion is formed in the center of the end face 23 of the piston rod 3B, and the end face 2 of the piston 4B is formed.
A projection 31 of a fitting portion in the axial direction is provided at a center portion on the 0 side, and the projection 31 is fitted into the hole 30 to ensure coaxiality between the piston rod 3B and the piston 4B. A counterbore hole 32 for accommodating the head of the bolt 22 is formed in the opening of the bolt through hole 25 of the piston 4B on the side of the chamber 7b.
Is formed so that the head of the bolt 22 does not protrude from the end face of the piston 4B.

In this embodiment, the piston rod 3
An O-ring groove 50A is provided in the outer peripheral portion of the contact portion between the end surface 20 of the piston 4B and the end surface 23 of the piston 4B.
The O-ring 51A is mounted on the ring groove 50A, and the piston 4B is assembled to the piston rod 3B in this state, whereby the outer periphery of the face-to-face contact portion between the distal end face 23 of the piston rod 3B and the end face 20 of the piston 4B. A sealing portion is formed in the portion to hydraulically isolate the facing contact portion from the rod-side chamber 7a and prevent pressure oil acting in the rod-side chamber 7a from entering the facing contact portion.

FIG. 7 shows a fourth embodiment of the present invention, in which a hole 30 and a protrusion 3 of the fitting portion shown in FIG.
1 is enlarged to form a hole 30C and a projection 31C, respectively.
The bolt screw hole 24 and the through hole 25 of the bolt 22 are formed in the hole 30C and the protrusion 31C.

Further, as in the third embodiment, a seal portion composed of an O-ring groove 50A and an O-ring 51A is provided on the outer peripheral portion of the facing contact portion between the distal end surface 23 of the piston rod 3C and the end surface 20 of the piston 4C. Provided, chamber 7 on the rod side
The pressure oil acting on the inside of the piston rod 3C is the tip end face 2 of the piston rod 3C.
It is configured to prevent intrusion into the facing contact portion between the rod 3 and the rod-side end surface 20 of the piston 4C.

FIG. 8 shows a fifth embodiment of the present invention, in which the positioning for securing coaxiality between the piston rod 3D and the piston 4D is replaced by a fitting portion and a pin 35 is used.
This is done by: Here, two pins 35 are used symmetrically on the diameter line as shown in FIG. When assembling, a pin hole 3 is formed in each of the end faces 20 and 23 while maintaining the coaxiality of the piston rod 3D and the piston 4D.
After the pins 6 and 37 are opened in advance and the pin 35 is press-fitted into one of the pin holes 36 and 37, the other pin hole is press-fitted into the pin 35 and positioned, and fixed with the bolt 22 in this state.

Further, as in the third embodiment, a seal portion composed of an O-ring groove 50A and an O-ring 51A is provided on the outer peripheral portion of the facing portion between the distal end surface 23 of the piston rod 3D and the end surface 20 of the piston 4D. Provided, chamber 7 on the rod side
The pressure oil acting on the inside of the piston rod 3D
It is configured to suppress intrusion into the facing contact portion between the piston 3D and the rod-side end surface 20 of the piston 4D.

According to the second embodiment shown in FIG. 5, the effects 1) to 6) can be obtained.

According to the embodiments shown in FIGS. 6 to 8, the effects of the above 1) to 8) can be obtained, and with respect to the effect of the above 6), the entire length of the rod is up to the piston end face. Therefore, the effective stroke of the hydraulic cylinder can be further lengthened.

Further, according to each of the embodiments shown in FIGS. 5 to 8, a fitting portion (second embodiment) between the inner peripheral surface of the piston recess and the outer peripheral surface of the piston rod or the tip of the piston rod. The O-ring groove 50 or 50 is formed in the outer peripheral portion (the third to fifth embodiments) of the face-to-face contact portion between the end face and the end face of the piston.
A and an O-ring 51 or 51A are provided with a seal portion, and pressure oil acting in the rod side chamber 7a is applied to the end face 23 of the tip of the piston rod and the rod end face 2 of the piston.
As described in the first embodiment, it is possible to avoid an increase in external force due to the oil pressure on the separation surface acting on the bolt 22, and to break or loosen the bolt 22, as in the first embodiment. A decrease in fastening strength due to the above-mentioned factors can be prevented, and the effect of improving the strength of the piston fastening portion can be ensured.

FIGS. 10 and 1 show a sixth embodiment of the present invention.
1 will be described. In the present embodiment, the seal portion is configured without using an O-ring.

In FIG. 10, pressing marks 60 formed by a metal flow tool are continuously or intermittently formed in the circumferential direction on the end face 20a of the piston 4E facing the chamber 7a on the rod side. The pressing mark 60 is formed by fixing the piston 4E to the piston rod 3 with the bolt 22 and then pressing the metal flow pressing tool against the piston end face 20a to apply an impact and press. A so-called metal flow phenomenon in which the metal of the part moves to the piston rod side occurs, and the recess 21 of the piston 4E
A contact pressing portion 61 having a stress distribution as shown in FIG. 11 is formed between the inner peripheral surface 21b and the outer peripheral surface of the piston rod 3, and the contact pressing portion 61 functions as a seal portion. That is, the contact pressing portion 61 causes the distal end surface 23 of the piston rod 3 and the rod-side end surface 20 (recessed surface) of the piston 4 to be fitted to the fitting portion between the inner peripheral surface 21b of the recess 21 of the piston 4E and the outer peripheral surface of the piston rod 3. A seal portion is formed that hydraulically isolates the face-to-face contact with the end face 21a) from the rod-side chamber 7a and prevents pressure oil acting in the rod-side chamber 7a from entering the face-to-face contact. .

Also in this embodiment, it is possible to avoid an increase in external force due to the hydraulic pressure on the separation surface acting on the bolt 22, and
A decrease in the fastening strength due to breakage or loosening of the piston can be prevented, and the effect of improving the strength of the piston fastening portion can be ensured.

Instead of forming the contact pressing portion 61 by the pressing mark 60 as described above, the fitting between the inner peripheral surface 21b of the recess 21 of the piston and the outer peripheral surface of the piston rod may be a tight fit. With this, a certain sealing effect can be expected. Further, the formation of the contact pressing portion 61 by the pressing mark 60 and the interference fit may be used together, and in this case, a higher sealing effect can be expected.

The seventh embodiment of the present invention will be described with reference to FIGS.
3 will be described. This embodiment shows another example in which a seal portion is formed without using an O-ring.

FIG. 12 shows a state before the piston 4F is fixed to the piston rod 3F by bolts after the tip of the piston rod 3F is fitted into the recess 21 of the piston 4F. No clamping force is applied in the axial direction. In this state,
The distal end face 23F of the piston rod 3F has a slightly curved concave shape as shown in FIG.
A gap 65 is formed between the distal end face 23F and the concave end face 21a of the piston 4F. In FIG. 12, the size of the gap 65 is exaggerated for convenience of illustration. The actual size of the gap 61 is, for example, about 20 μm in a dimension g near the center of the end face.

When the piston 4F is fastened to the piston rod 3F thus configured with the bolt 22 (see FIG. 1),
The gap 65 is eliminated by the fastening force of the bolt 22, and the distal end face 23F of the piston rod 3F and the concave end face 21 of the piston 4F are formed.
As a result, the outer peripheral portion is strongly pressed against the outer peripheral portion, and as a result, a contact pressing portion 66 having a stress distribution as shown in FIG.
6 functions as a seal portion. That is, the pressing contact portion 66
As a result, the facing contact portion is hydraulically isolated from the rod-side chamber 7a on the outer peripheral portion of the facing contact portion between the distal end surface 23F of the piston rod 3F and the recessed end surface 21a of the piston 4F. A seal portion is formed to prevent pressure oil acting on the contact portion from entering the facing contact portion.

In the present embodiment as well, it is possible to avoid an increase in external force due to the hydraulic pressure on the separation surface acting on the bolt 22, and
A decrease in the fastening strength due to breakage or loosening of the piston can be prevented, and the effect of improving the strength of the piston fastening portion can be ensured.

It should be noted that some hydraulic cylinders include a cushion device for cushioning the impact at the stroke end of the piston rod, and the above-described embodiment is applied to the hydraulic cylinder piston fastening structure without such a cushion device. Although the invention is applied, Japanese Patent Application No. 10-14 / 1998
FIGS. 8 to 12 of No. 9467 show an embodiment in which a piston of a hydraulic cylinder provided with a cushion ring (cushion device on the rod side) is directly fixed to a piston rod with bolts. A hydraulic cylinder having a cushion plunger (bottom side cushion device) provided on a piston rod directly fixed to a piston with a bolt is shown, and the present invention may be applied to a device provided with such a cushion device. Of course, also in this case, the same effect as the above embodiment can be obtained.

[0065]

According to the present invention, 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. The effect of improving the assemblability and serviceability is obtained, and furthermore, the pressure oil acting in the chamber on the rod side is suppressed from entering the facing contact portion between the piston rod and the piston, and the strength of the piston fastening portion is improved. You can be sure.

[Brief description of the drawings]

FIG. 1 is a sectional view of a hydraulic cylinder including a piston fastening structure according to a first embodiment of the present invention.

FIG. 2 is a front view of a piston fastening portion shown in FIG.

FIG. 3 is a view showing deformation of a piston when a cylinder is operated to supply pressure oil to a rod-side chamber and contract a hydraulic cylinder.

FIG. 4 is a diagram showing an open portion at an outer peripheral portion of a face-to-face contact portion between a tip end face of a piston rod and a piston end face caused by deformation of a piston when a cylinder is actuated, from the IV-IV direction in FIG. FIG.

FIG. 5 is a sectional view of a piston fastening structure of a hydraulic cylinder according to a second embodiment of the present invention.

FIG. 6 is a sectional view of a piston fastening structure of a hydraulic cylinder according to a third embodiment of the present invention.

FIG. 7 is a sectional view of a piston fastening structure of a hydraulic cylinder according to a fourth embodiment of the present invention.

FIG. 8 is a sectional view of a piston fastening structure of a hydraulic cylinder according to a fifth embodiment of the present invention.

FIG. 9 is a front view of a piston fastening portion shown in FIG. 8;

FIG. 10 is a sectional view of a piston fastening structure of a hydraulic cylinder according to a sixth embodiment of the present invention.

FIG. 11 is a view showing a stress distribution of a tightening force generated between an inner peripheral surface of a piston recess and an outer peripheral surface of a piston rod due to metal flow.

FIG. 12 is a sectional view of a piston fastening structure of a hydraulic cylinder according to a seventh embodiment of the present invention.

FIG. 13 is a diagram showing a stress distribution of a tightening force generated at a face-to-face contact portion between the distal end face of the piston rod and the piston end face due to the concave shape of the piston rod end face.

FIG. 14 is a cross-sectional view of a conventional piston fastening structure of a hydraulic cylinder.

FIG. 15 is a sectional view of a piston fastening structure of a hydraulic cylinder according to another related art.

FIG. 16 is a diagram showing a state of stress acting on a male screw portion of a piston rod.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Hydraulic cylinder 2 Cylinder main body 3 Piston rod 4 Piston 5 Tube 6 Rod side cylinder head 7a, 7b Chamber 8, 9 Supply / discharge port 20 Piston rod end surface 20a Piston end surface facing rod side chamber 21 Recess 21a Bottom surface ( 21b Inner circumferential surface of piston recess 22 Bolt 23 Piston rod end surface 24 Bolt screw hole 25 Bolt through hole 50, 50A O-ring groove (seal part) 51, 51A O-ring (seal) Part) 60 pressing mark 61 contact pressing part (seal part) 65 gap 66 contact pressing part (seal part)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsuhiro Yoshimoto 650, Kandachicho, Tsuchiura-shi, Ibaraki F-term in the Tsuchiura Plant of Hitachi Construction Machinery Co., Ltd. (Reference) 3H081 AA03 BB02 CC23 CC24 DD02 EE27

Claims (5)

[Claims] In 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, a rod-side end face of the piston is attached to an end face of the tip of the piston rod. In a state of at least partial face-to-face contact, a bolt is inserted into a bolt screw hole provided in the piston rod from a bolt through hole opened in the piston and tightened, and the piston is directly fixed to the piston rod with the bolt. A hydraulic cylinder provided with a seal portion for preventing pressure oil acting in a rod-side chamber from entering a face-to-face contact portion between an end surface of a tip end of the piston rod and a rod-side end surface of the piston. 2. The hydraulic cylinder according to claim 1, wherein said piston has a concave portion into which a tip of said piston rod is fitted, and said seal portion has an inner peripheral surface of said concave portion of said piston and an outer peripheral surface of said piston rod. A hydraulic cylinder provided at a fitting portion with a surface. 3. The hydraulic cylinder according to claim 1, wherein the seal portion is provided on an outer peripheral portion of a face-to-face contact portion between an end surface of a tip end of the piston rod and a rod-side end surface of the piston. Hydraulic cylinder. 4. The hydraulic cylinder according to claim 1, wherein said seal portion is formed of an O-ring. 5. The hydraulic cylinder according to claim 1, wherein said seal portion is constituted by a contact pressing portion between said piston rod and said piston.