JPH11344009A - Piston fastening structure of hydraulic cylinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston fastening structure for hydraulic cylinder, which can heighten the strength of the piston fastening part using a simple configuration without use of any special high-strength material to a piston rod or subjecting material to a heat treatment. SOLUTION: A recess 21 as an axial direction fitting part is formed at the end face 20 of a piston 4 on its piston rod 3 side, and the tip of the piston rod 3 is fitted in the recess 21 so as to ensure concentricity. An axially directed thread hole 24 is provided in the forefront end face 23 of the piston rod 3, while a bolt inserting hole 25 directed along the axis is formed in the piston 4, and from the hole 25, a bolt 22 is inserted into the thread hole 24 and fastened for fixation of the piston 4 in the condition that the piston end face 20 is in face-to-face contact with the forefront end face 23 of the piston rod 3, and thereby fastening with the piston rod 3 is established.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure for fastening a piston of a hydraulic cylinder, and more particularly to a structure for fastening a piston of 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. 13, the hydraulic cylinder is provided at a cylinder body 102, a piston rod 103 moving within the cylinder body 102, and a tip of the piston rod 103.
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. 14 shows another example of a conventional piston fastening structure. This example is shown in FIG.
In this state, a circular ring 103k is further provided in the piston insertion portion 103j for inserting the piston 104, and a circular ring is formed in the circular groove 103k in a state where the piston 104 is fitted until the piston 104 comes into contact with the step portion 103m. A half ring-shaped flange 160 divided into two in the direction is fitted,
By fixing the flange 160 to the piston 104 with bolts 170, the piston 104 is fixed and fastened to the piston rod 103. In this case, the chamber 10 in the cylinder body 102 separated by the piston 104
Piston insertion part 103 for sealing between 7a and 107b
An O-ring 180 is provided between j and the piston 104.

[0005]

In the hydraulic cylinder shown in FIG. 13, 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.

In the conventional piston fastening structure shown in FIG. 13, when the pressure of the chamber 107a or 107b acts on the piston 104, the piston 104 closes a nut 112 on a 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. 15 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 tip end side of the piston insertion portion 103j. As can be seen from this figure, a maximum tensile stress is applied to the first thread portion on the external thread portion 103g, and damage to the external thread portion 103g occurs at 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. 14, 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,
This configuration requires two half-ring shaped flanges 160, which are further separated by piston 104
O-ring 18 is inserted between piston insertion portion 103j and piston 104 to seal between chambers 107a and 107b.
0 is required, and the number of parts increases.

An object of the present invention is to provide a hydraulic cylinder piston fastening structure that 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. .

[0010]

(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 piston fastening structure for a hydraulic cylinder, a screw provided in a 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 facing the end surface of the tip of the piston rod. A bolt is inserted into the hole and tightened, and the piston is directly fixed to the piston rod with the bolt.

[0011] By directly fixing the piston to the piston rod with a bolt as described above, the force applied to the piston during operation of the hydraulic cylinder is received by the bolt,
Although tensile stress acts on the bolt, the material of the bolt is strong, so that sufficient strength can be obtained. Further, since the threaded portion of the threaded hole of the piston rod is a female thread, there is no problem in strength even if the rod material is not so strong. 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.

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

Furthermore, since the conventional small-diameter piston insertion portion becomes unnecessary, the piston rod can be a round bar having no step, and the problem of breakage at the conventional step portion is eliminated.

(2) In the above (1), preferably,
A plurality of the screw holes and a plurality of bolt through holes are formed, and the piston is fixed to the piston rod by using a plurality of the bolts.

By using a plurality of bolts as described above, the tightening torque of each bolt can be reduced, and assembly and disassembly become easy.

Further, since the tightening torque of one bolt is small, the bolt can be loosened manually without using a large-scale dedicated machine, which has been conventionally required, and the serviceability is improved.

(3) In the above (1), preferably,
An axial fitting portion is formed on at least one of the end face of the distal end of the piston rod and the end face on the rod side of the piston to ensure coaxiality between the piston and the piston rod.

(4) In the above (1), a pin may be driven into the end face at the tip of the piston rod and the end face on the rod side of the piston to ensure coaxiality between the piston and the piston rod.

[0019]

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. 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 surface 2 of piston 4 on piston rod 3 side
0 has a recess 21 as an axial fitting portion,
By fitting the tip of the piston rod 3 into the recess 21, the piston 4 is mounted and coaxiality with the piston rod 3 is secured. In addition, an axial 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 piston 4, and the end face 20 of the piston 4 is formed in the end face 23 of the tip of the piston rod 3. The piston 4 is fixed by inserting and tightening the bolt 22 from the bolt through hole 25 to the screw hole 24 in the face-to-face contact state, 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 the present 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 a plurality of bolts 22.
Will receive it. At this time, a tensile stress acts on the bolt 22, but if the material of the bolt 22 is made strong, the strength of the bolt 22 is sufficient. Further, since the threaded portion of the threaded hole 24 of the piston rod 3 is a female thread, there is no problem in strength even if the rod material is not so strong.

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

1) In the conventional general piston fastening structure shown in FIG.
(See FIG. 13).
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.
It is easy to make the material of the bolt 22 strong,
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. 14, two flanges 160 and O-rings 180 were required, and the number of parts was large. However, such parts are unnecessary in the present invention, and the minimum number is required. It can be configured by the number of parts.

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

6) The entire 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 prior art.

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, the piston assembly is disassembled and maintenance is performed. 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. 13). 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.

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. 3 shows a second embodiment of the present invention, in which a piston 4A is fastened to a piston rod 3A with 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.

FIG. 4 shows a third embodiment of the present invention. 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 chamber 7b side.
Is formed so that the head of the bolt 22 does not protrude from the end face of the piston 4B.

FIG. 5 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 screw hole 24 and the through hole 25 of the bolt 22 are
And the projection 31C.

FIG. 6 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.

According to the embodiment shown in FIG.
To 6) are obtained.

According to each of the embodiments shown in FIGS.
In addition to the effects 1) to 8), the effect of the above item 6) is such that the entire length of the rod is up to the end surface of the piston 4B, so that the effective stroke of the hydraulic cylinder 1 can be further increased.

FIGS. 8 to 12 show the embodiment shown in FIGS. 1 and 2 to 6 in which a floating rod-side cushion ring is provided.

In FIG. 8, a small-diameter portion 41 is provided at the tip of the piston rod 3 with the step portion 40 as a boundary.
A cushion ring 42 is inserted into the small-diameter portion 41 so as to be freely fit in the radial and axial directions, and the piston 4 is fixed to the tip of the small-diameter portion 41 with the bolt 22 as in the embodiment shown in FIG. At the end of the small diameter portion 41 on the side of the step portion 40, an R portion 43 serving as a relief portion at the time of polishing the small diameter portion 41 is formed. A tapered portion 44 is formed at an end of the cushion ring 42 on the piston rod side, and a plurality of grooves 45 are formed on the piston 4 side in the thickness direction of the cushion ring 42. This floating type cushion ring 42 is used to reduce the impact at the stroke end when the hydraulic cylinder is extended.

That is, when the hydraulic cylinder is extended, the rod-side cushion ring 42 extends from the tapered portion 44 to the cushion-ring fitting portion provided on the inner end portion 6a of the rod-side cylinder head 6 (see FIG. 1) near the stroke end. When it enters, the oil passage of the inner end portion 6a is narrowed, a cushion pressure is raised in the chamber 7a, the stroke speed is reduced, and the impact at the stroke end is reduced. At this time, the cushion ring 42 is movable in both the radial direction and the axial direction. When the tapered portion 43 of the cushion ring 42 enters, the cushion ring 42 follows the shape of the hole of the cushion ring fitting portion. There is no fear of galling between the fitting portion 42 and the fitting portion. Further, when the cushion ring 42 enters, a cushion pressure is generated in the chamber 7a, and a pressure difference is generated between the side of the cushion ring 42 that enters the fitting portion and the piston 4 side (the chamber 7a side).
Is pressed against the end face of the step portion 40 so that the pressure oil does not flow to the supply / discharge port 8 between the small-diameter portion 41 as the cushion ring insertion portion and the inner peripheral surface of the cushion ring 42. Then, after reaching the stroke end, when the piston rod 3 starts moving in the contracting direction (rightward in the figure) and the cushion ring 42 comes out of the fitting portion,
Pressure oil from the supply / discharge port 8 flows into the chamber 7a through a gap between the outer peripheral surface of the cushion ring 42 and the inner peripheral surface of the fitting portion. At this time, the cushion ring 42 is pressed against the piston 4 by the hydraulic pressure from the supply / discharge port 8, but since the groove 45 is provided on the piston-side end surface of the cushion ring 42, the pressure oil is supplied to the rod as the cushion ring insertion portion. It flows between the small diameter portion 41 and the inner peripheral surface of the cushion ring 42, flows into the chamber 7a through the groove 45,
It works out well.

9, 10, and 12, similarly, a rod small diameter portion 41 which is a cushion ring insertion portion is provided, and the rod small diameter portion 41 is provided with a cushion ring 42.
Are loosely fitted, and the pistons 4A, 4B, 4D are fixed to the distal end of the rod small diameter portion 41 with bolts 22 or 22A.

In the embodiment shown in FIG. 11, the length of the protrusion 31C of the piston 4C is longer than that of the embodiment shown in FIG. The projection 31C is fitted into a recess 30C formed in the end surface 23 of the piston rod 3C to form an axial fitting portion, and the piston 4C 'is fixed by a bolt 22'.

When a floating type cushion ring is inserted in the conventional piston fastening structure shown in FIG. 13, the piston insertion portion 103j of the piston rod (see FIG. 13) is further advanced to the rod small diameter portion which is the cushion ring insertion portion. Side, and the screw size of the male screw portion 103g of the piston insertion portion 103j is reduced, making it more difficult to maintain strength.

In the embodiments shown in FIGS. 8 to 10 and FIG.
It is only necessary to provide the rod small diameter portion 41 as the cushion ring insertion portion, and it is not necessary to provide a small diameter portion for inserting the piston. For this reason, the effect described in the embodiment of FIGS. 1 and 2 to 6 can be obtained such that the piston rod 3 can be manufactured at low cost by providing the floating type rod-side cushion ring.

In the embodiments of FIGS. 8 to 10 and FIG. 12, the external thread portion, which is the weakest portion of the rod, is eliminated.
The life of the piston rod is significantly improved. However, since there is a rod small diameter portion 41 which is a cushion ring insertion portion, if there is any problem with the piston rod,
Steps 40 and R caused by existence of rod small diameter portion 41
There is strength at the part 43. When the piston operates, this step 4
Concentrated stress repeatedly acts on the 0 and R portions 43, and the portions are easily broken. In the embodiment of FIG. 11, the rod small diameter portion 41 is also eliminated by providing a cushion ring insertion portion on the protrusion 31C on the piston 4C 'side using the structure of the embodiment of FIG. For this reason, the piston rod 3C is a round bar having the same overall length, and there is no problem of damage to the rod itself, and the life of the piston rod can be further improved.

[0049]

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

1) Since it is not necessary to provide a male thread on the piston rod, 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.
Piston rods can be made inexpensively with low cost materials.

2) It is easy to make the material of the bolt strong, and the strength of the piston fastening portion can be improved with a simple structure, and the life of the piston rod can be improved.

3) By fixing with bolts, the fatigue strength against external force is also improved.

4) Components other than bolts are unnecessary, and can be configured with a minimum number of components.

5) Since the conventional 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 entire length of the rod is the length up to the head of the bolt, and the effective stroke of the hydraulic cylinder can be lengthened.

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

8) When a plurality of bolts are used, since the tightening torque of one bolt is small, the bolt can be loosened manually without using a large-scale dedicated machine conventionally required. , Serviceability is improved.

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

FIG. 4 is a sectional view of a piston fastening structure of a hydraulic cylinder according to a third embodiment of the present invention.

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

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

FIG. 7 is a front view of a piston fastening portion shown in FIG. 6;

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

FIG. 9 is a sectional view of a piston fastening structure of a hydraulic cylinder according to still another embodiment of the present invention.

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

FIG. 11 is a sectional view of a piston fastening structure of a hydraulic cylinder according to still another embodiment of the present invention.

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

FIG. 13 is a cross-sectional view of a conventional piston fastening structure of a hydraulic cylinder.

FIG. 14 is a sectional view of a piston fastening structure of a hydraulic cylinder according to another related art.

FIG. 15 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 face 21 Recess 22 Bolt 23 Piston rod end face 24 Screw hole 25 Bolt Through hole 41 Rod small diameter portion which is a cushion ring insertion portion 42 Cushion ring 43 R portion 44 Tapered portion 44 Groove

Claims (4)

[Claims] 1. A piston fastening structure for a hydraulic cylinder in which a piston is fastened to a tip of a piston rod and a cylinder body is divided into a chamber on a rod side and a chamber on a bottom side, wherein a piston rod is attached to an end face of the tip of the piston rod. With the side end faces at least partially facing each other, insert a bolt into the screw hole provided in the piston rod from the bolt through hole opened in the piston and tighten it, and fix the piston directly to the piston rod with this bolt A piston fastening structure for a hydraulic cylinder, characterized in that: 2. A piston fastening structure for a hydraulic cylinder according to claim 1, wherein a plurality of said screw holes and a plurality of bolt through holes are respectively formed, and said piston is fixed to said piston rod using a plurality of said bolts. Hydraulic cylinder piston fastening structure. 3. The piston fastening structure for a hydraulic cylinder according to claim 1, wherein at least one of an end face of the tip of the piston rod and an end face of the piston on a rod side is formed with an axial fitting portion, and the piston and the piston are provided. A piston fastening structure for a hydraulic cylinder, wherein the coaxiality of the rod is secured. 4. A piston fastening structure for a hydraulic cylinder according to claim 1, wherein a pin is driven into an end surface of a tip end of said piston rod and an end surface of said piston on a rod side to ensure coaxiality between said piston and said piston rod. A piston fastening structure for a hydraulic cylinder.