JPH11173308A - Hydraulic cylinder with cushion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep durability of a piston rod in an excellent state by increasing the strength of the portion of a step required for arrangement of a cushion device without increasing the diameter of the piston rod to a value more than necessary and performing in particular a large scale of heat treatment. SOLUTION: A step D2 is formed between a ring mounting device 3b formed to mount a cushion ring 11, of which a cushion device consists, on a piston rod 3 and a rod body 3a. A curved part C in a shape curved in a recessed part is formed at the transfer part from the vertical wall V of the step D2 to the outer peripheral surface R of a ring mount part 3b. By partially quenching a portion, ranging from the curved part C to a vertical wall V, throughout the whole periphery thereof in addition to a plan of dispersion of a stress to form a partial quenched layer H, strength is partially improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic cylinder used as a hydraulic actuator or the like, and to a hydraulic cylinder with a cushion device provided with a cushion device that exerts a buffering action when displaced to the extension side.

[0002]

2. Description of the Related Art A hydraulic cylinder used as a hydraulic actuator is configured so that a piston connected to a piston rod slides in the cylinder, and the interior of the cylinder is divided into a rod chamber and a bottom chamber by the piston. The compartment is formed. The distal end of the piston rod and the end of the cylinder are pivotally mounted between predetermined members. If pressure oil is supplied to the bottom chamber and the rod chamber is connected to the tank, the piston rod will extend, and conversely, pressure oil will be supplied to the rod chamber and the bottom chamber will be connected to the tank. Then, the piston rod contracts. When the hydraulic cylinder is operated in the extension or contraction direction with a large load acting between the piston rod and the cylinder, a large impact is applied at the stroke end.

[0003] As described above, a hydraulic cylinder on which a large load acts is provided with a cushion device for reducing an impact near the stroke end of the piston rod. In general, a cushion device narrows a flow path for discharging hydraulic oil from a rod chamber or a bottom chamber in a cylinder so as to establish a back pressure in these chambers. For example, a cushion device that operates on the extension side of a piston rod is provided by fitting a cushion ring having a predetermined outer diameter to a piston rod, and a cushion flow passage that communicates with a hydraulic oil passage is formed in a rod chamber. The cushion member is fitted into the cushion flow path near the stroke end, and the pressure is narrowed as the cushion member enters the cushion flow path, thereby generating a back pressure in the rod chamber. it can.

[0004] By exerting a smoother cushioning effect,
In order to stop smoothly, the cushion stroke must be set to a predetermined length, the diameter difference between the outer diameter of the cushion member and the hole diameter of the cushion flow path must be as small as possible, and the cross-sectional area of the flow path must be as small as possible. No. As described above, if the diameter difference between the cushion member and the cushion flow path is reduced, even if the axis of the cushion member is slightly displaced with respect to the axis of the cushion flow path due to a processing error, an assembly error, or the like, metal contact does not occur. As a result, there is a possibility that abrasion powder or the like may be generated due to the occurrence of galling and fitting, and in a severe case, the cushion member or the like may be damaged. Therefore, there is a limit in reducing the diameter difference between the outer diameter of the cushion member and the inner diameter of the cushion flow path. If the diameter difference is too small, the flow path cross-sectional area at the time of supply of pressurized oil from the hydraulic oil flow passage to the bottom chamber of the cylinder becomes small when the piston rod is extended. Until the cushion member escapes from the bottom chamber, the supply of the pressure oil to the bottom chamber is not smoothly performed. During that time, not only does the movement speed of the piston decrease, but also noise occurs when the cushion member escapes from the cushion flow path.

[0005] In consideration of the above points, even if the cross-sectional area of the flow path is extremely small in the direction in which the cushion function is exhibited, the cushion member does not come into metallic contact with the cushion flow path.
A cushion device that increases the cross-sectional area of the flow path in the direction in which the cushion member comes out of the cushion flow path is conventionally known.

An example of a known cushion device will be described with reference to FIGS. 2 and 3. FIG. First, in FIG. 2, 1 is a cylinder, 2 is a piston, and 3 is a piston rod. The cylinder 1 has a cylindrical cylinder tube 1a, a cap 1b is connected and fixed to one end of the cylinder tube 1a, and a rod lead-out portion 1c is fixed to the other end side. . Piston 2 is piston rod 3
Is fixed to a part on one end side. Piston rod 3
, As is clear from FIG. 3, it has a shape with a step d _1, d ₂ of the two-stage which is smaller in diameter on the tip side of the rod main body 3a ring mounting portion 3b, in order of the piston attachment portion 3c.
First, the piston 2 is fitted into the smallest-diameter piston mounting portion 3c and a nut 4 is fastened. The tightening force of the nut 4 allows the piston 2 to be connected to the piston mounting portion 3c and the ring mounting portion. It is fixed as pressed against the step d ₁ between 3b. Therefore, piston 2
Is constantly pressed against the step d ₁ by the tightening force of the nut 4. The piston 2 defines the inside of the cylinder 1 into a bottom chamber 5 and a rod chamber 6.
The bottom chamber 5 and the rod chamber 6 are provided with hydraulic oil passages 7, 8, respectively.

When pressure oil is supplied to the hydraulic oil flow passage 7 communicating with the bottom chamber 5 and the hydraulic oil flow passage 8 communicating with the rod chamber 6 is connected to the tank, the piston 2 slides toward the rod outlet portion 1c and slides. The piston rod 3 extends. When hydraulic oil is supplied to the hydraulic oil passage 8 and the hydraulic oil passage 7 is connected to the tank, the piston 2 slides toward the cap 1b and the piston rod 3 contracts. Therefore, the mounting portion 9 provided on the cap 1b of the cylinder 1 and the piston rod 3
For example, when the mounting portion 10 provided at the front end of the movable member is pivotally connected between the fixed member and the movable member, the movable member can be driven.

Accordingly, a cushion device which exerts a cushioning function near the stroke end in the extension direction of the piston rod 3 will be described below. A similar cushion device is also provided in the contracting direction of the piston rod 3, but illustration thereof is omitted. The ring mounting portion 3b having an intermediate diameter of the piston rod 3 is for mounting the cushion ring 11. The inner diameter of the cushion ring 11 is larger by a predetermined dimension than the outer diameter of the ring mounting section 3b, and the length in the axial direction is shorter than the ring mounting section 3b by a predetermined dimension. Thereby, an annular gap is formed between the cushion ring 11 and the ring mounting portion 3b, and the cushion ring 11 is in contact with the end surface of the piston 2 and the state between the ring mounting portion 3b and the rod body 3c. It is movable within a limited range so as to come into contact with the step d2 between the _two .

On the other hand, the rod lead-out portion 1 of the cylinder 1
A cushion flow path 12 communicating with the hydraulic oil flow path 8 is formed in c. Here, the cushion flow path 12 is composed of a circular path smaller than the inner diameter of the cylinder tube 1a surrounded by the inner wall surface 12a of the rod lead-out portion 1c, the piston rod 3 extends, and the cushion ring 11 12, the cushion flow path 12
The flow path of the return oil on the side of the rod chamber 6 that flows out through the hole is restricted, and as a result, a back pressure is generated in the rod chamber 6, and the back pressure causes the cushioning action in the extending direction of the piston rod 3. Demonstrate.

The cushion ring 11 moves based on the pressure difference between the cushion flow path 12 and the rod chamber 6. When the pressure in the rod chamber 6 becomes high, the cushion ring 11 moves.
Abuts on the step d _2, and when a high pressure acts on the cushion flow path 12 side, the cushion ring 11 abuts on the end face of the piston 2. An annular gap is formed between the inner surface of the cushion ring 11 and the outer surface of the ring mounting portion 3b of the piston rod 3, and this annular gap functions as a one-way flow path. That is, when the cushion ring 11 is in contact with the step d ₂ (when the piston rod 3 reaches the vicinity of the end of the extension stroke), the annular gap does not function as a flow path, and the cushion ring 11
(When the reduction stroke of the piston rod 3 is started), the annular gap functions as a flow path for flowing hydraulic oil from the cushion flow path 12 to the rod chamber 6. As described above, in order to allow the annular gap to function as a one-way flow path, a plurality of grooves 13 are formed in the end face of the cushion ring 11 on the side facing the piston 2 so as to penetrate in the thickness direction. Then, the total flow path cross-sectional area by the plurality of grooves 13 is made substantially equal to the flow path cross-sectional area by the annular gap. Further, when the cushion ring 11 enters the cushion flow channel 12, in order to smoothly and surely enter the cushion flow channel 12, an outer peripheral edge of the cushion ring 11 on the side facing the step d ₂ is provided. Is formed with an attraction taper portion 11a.

Therefore, when the hydraulic oil passage 7 is connected to a hydraulic source such as a hydraulic pump and the hydraulic oil passage 8 is connected to a tank when the piston rod 3 is in the contracted state, the pressure in the bottom chamber 5 becomes high. Since the pressure in the rod chamber 6 becomes low, the piston rod 3 extends. At this time, if a large load acts on the piston rod 3 in the extension direction, the pressure difference between the bottom chamber 5 and the rod chamber 6 becomes extremely large, and the piston rod 3 is rapidly displaced. However, near the stroke end, the cushion ring 11 enters the cushion flow path 12 and enters the cushion stroke, and the flow path of the return oil is narrowed. As a result, a back pressure is generated on the rod chamber 6 side, so that the difference between the pressure of the bottom chamber 5 acting on both surfaces of the piston 2 and the pressure on the rod chamber 6 side is reduced, and the movement is decelerated. At this time, since the rod chamber 6 pressure than the working fluid flow passage 8 is increased, as a result of the cushion ring 11 by the action of this pressure unidirectional flow path is pressed against the step d ₂ is closed, the return oil cushion Since the gas flows only through the gap between the ring 11 and the cushion flow path 12, the pressure in the rod chamber 6 becomes higher and the cushion ring 1
Since the length of the throttle flow path increases in accordance with the degree of entry into the first cushion flow path 12, when approaching the stroke end, the back pressure in the rod chamber 6 further increases and smoothly stops at the stroke end. And the impact is remarkably reduced.

The cushion ring 11 is a piston rod 3
When the cushion ring 11 enters the cushion flow path 12, the entire piston rod 3 or its ring insertion portion 3 b is loosely fitted into the ring insertion portion 3 b.
Irrespective of this, it follows the cushion flow path 12 side. Accordingly, the dimensional difference between the outer diameter of the cushion ring 11 and the inner diameter of the inner inner wall surface 12a constituting the cushion flow path 12 is made very small, the flow path cross-sectional area of the throttle flow path is made extremely small, and a larger cushion is provided. Even if the function is exerted, there is no danger that the cushion ring 11 is in metal contact with the inner inner wall surface 12a to cause galling, fretting, etc., and there is no danger that the space between them may be damaged or abrasion powder may be generated. Absent.

On the other hand, when pressurized oil is supplied to the hydraulic oil flow passage 8 in order to reduce the piston rod 3 from its stroke end, the cushion ring 11 is pushed by the action of the pressure from the hydraulic oil passage 8, It separates from the step wall 13 and contacts the piston 2. As a result, in addition to the flow path on the outer surface side of the cushion ring 11, a one-way flow path including the groove 13 is formed between the cushion ring 11 and the piston 2. 3 is extended smoothly and quickly, and the noise when the cushion ring 11 comes out of the cushion flow path 12 is also eliminated.

[0014] The cushioning action at the stroke end as described above is necessary to reduce the impact at the stroke end when a large load acts on the hydraulic cylinder. One example of a hydraulic cylinder used as an actuator under severe conditions in which an extremely large load acts is a front working mechanism of a hydraulic shovel shown in FIG. In the figure,
Reference numeral 20 denotes a lower traveling body, and reference numeral 21 denotes an upper revolving body. The upper revolving body 21 is provided with a front working mechanism 22 for performing operations such as excavation of earth and sand. The front working mechanism 22 includes a boom 23 connected to the upper swing body 21 so as to be capable of raising and lowering,
An arm 25 connected to a tip of the boom 23 so as to be rotatable up and down around a shaft 24, and a bucket connected to a tip of the arm 25 via a shaft 26 and rotatable around the axis of the shaft 26. 27. The boom 23, the arm 25, and the bucket 27 constituting the front working mechanism 22 are driven by a boom cylinder 23a, an arm cylinder 25a, and a bucket cylinder 27a, respectively. The connection of the bucket cylinder 27a to the bucket 27 is performed via a link mechanism 28.

Each of these cylinders 23a, 25a, 27a
The load acting on the boom cylinder 23
a is the largest, and then the load acting on the arm cylinder 25a is large. The bucket cylinder 27a has a smaller load as compared with the boom cylinder 23a and the arm cylinder 25a. However, since the boom cylinder 23a and the arm cylinder 25a are mounted on a portion that does not hinder the excavation operation of the earth and sand, a hydraulic cylinder having a certain size can be used. Therefore, the outer diameter is restricted as compared with the boom cylinder 23a and the arm cylinder 25a, and a small hydraulic cylinder must be used. In any case, when performing work such as excavation of earth and sand, each of the cylinders 23a, 25a, and 27a as hydraulic actuators for driving the front working mechanism 22 is repeatedly and frequently used in a state where an extremely large load is applied. Stretching,
Or shrink it. Since the piston rod in these hydraulic cylinders directly acts on the load and slides on the cylinder, the strength and the like are appropriately set according to the magnitude and properties of the acting load. .

[0016]

A hydraulic cylinder, such as a hydraulic cylinder for driving a front working mechanism of a hydraulic shovel, which operates so as to expand and contract frequently under an extremely high load is applied. Means that a large load repeatedly acts on the piston rod 3 in the pulling direction and the compression direction. As a result, the piston rod 3 may be damaged by the load acting repeatedly. In particular, since the piston rod 3 is provided with a step d ₂ for mounting the cushion ring 11, stress is concentrated on the step d ₂ , resulting in severe damage at this portion and in severe cases, There is a problem of breaking.

Therefore, it is necessary to improve the strength of the piston rod 3. As a measure for this, it is conceivable to increase the diameter of the piston rod 3. However, since the piston 2 is connected to the piston rod 3 and this piston 2 must have a predetermined pressure receiving area, if the diameter of the piston rod 3 is increased, the diameter of the piston 2 must also be increased. Therefore, the overall configuration of the hydraulic cylinder is increased in size and weight. In addition, when the installation space is limited as in the above-described bucket cylinder 27a, a large-sized hydraulic cylinder having a large outer diameter cannot be used.

As described above, it is not always advisable to increase the diameter of the piston rod 3 to improve its strength. As another measure for improving the strength of the piston rod 3, it is conceivable to improve the strength by heat treatment such as quenching. However, when the stroke of the hydraulic cylinder is long, the overall length of the piston rod 3 is correspondingly long. Therefore, if such a long piston rod 3 is quenched, there is a disadvantage that it becomes extremely expensive. Therefore, when the cushion device using the cushion ring is provided in the hydraulic cylinder, the cushion device is actually provided in the hydraulic cylinder in spite of the extremely advantageous points such as low noise due to reduction of impact, suppression of vibration, and the like. At present, there is a great restriction from the viewpoint of the strength of the piston rod and the like.

In order to solve the problems of the prior art as described above, the present inventors have conducted intensive research on the load acting on the piston rod in providing the hydraulic cylinder with the cushion device. By obtaining the knowledge shown, the inventors have completed the invention. Thus, the object of the present invention is to partially increase the diameter of the piston rod without necessity, or to perform the extraordinarily large heat treatment without partially strengthening the portion of the step required for providing the cushion device. To improve the durability of the piston rod.

First, as shown in FIG. 5, when a large inertial load F is acting on the piston rod 3,
When a pressure enough to overcome the load F is applied to the bottom chamber 5 to extend the piston rod 3, this pressure acts on the pressure receiving surface 2a of the piston 2 in the direction of the arrow, and as a result, the piston rod A load is applied to 3 in a direction compressed in the axial direction. Conversely, when the extending piston rod 3 is contracted, pressure is applied to the inside of the rod chamber 6. As a result, pressure enough to overcome the load F is exerted on the pressure receiving surface 2 b of the piston 2 on the rod chamber 6 side. Since it acts in the direction of the arrow, a load in the pulling direction acts on the piston rod 3.

Here, if the piston rod 3 has a uniform diameter over the entire length, there is no significant problem in terms of its strength, but since the piston rod 3 has the piston 2 and the cushion ring 11 attached thereto, In this case, two steps d ₁ and d ₂ are formed. For this reason, concentrated stress based on the compressive load and the tensile load is generated at these steps d ₁ and d ₂ . Here, in a state where the inertial load F is acting on the piston rod 3, or the hydraulic cylinder is extended, when or reduced, the step d ₁ and the ring fitting portion from the piston attachment portion 3c to the ring fitting portion 3b the level difference d ₂ to the rod main body 3a from 3b, stress shown in FIG. 6, respectively, it will act. In the figure, the dotted line indicates the stress concentration in the step d _1, also shows the stress concentration in the step d ₂ in solid lines.

Here, the piston 2 has a step d ₁ and a nut 4
And the piston 2 is pressed against the step d ₁ by a strong tightening force. Therefore, the step d ₁
As the load acting on the hydraulic cylinder, the tensile force is initially applied by the amount of this pressure contact force, and the load value itself at this part is high, but the fluctuation range of the stress due to the hydraulic pressure during the operation of the hydraulic cylinder Is relatively small. In contrast, by the structure so as to form a one-way flow path in the cushion ring 11, because the site of the step d ₂ is not applied is special external force, compression by hydraulic pressure acting upon the hydraulic cylinder actuating the load and tensile load, the fluctuation range of the compressive stress during a stress when tensile acting on the site of the step d ₂ becomes large and the larger the inertial load, the fluctuation range of the stress becomes extremely large .

The step d ₂ in the piston rod 3
It is not only the compressive stress and the tensile stress that act on the part. When a load acts in the direction of compressing the piston rod 3, normally, a force acts on the piston rod 3 not only in the axial direction but also in the bending direction. Here, since the distal end of the piston rod 3 is connected to the piston 2, the fulcrum position of the bending force acting on the piston rod 3 is a connection portion to the piston 2.
When a large load is applied to the piston rod 3 and a load is applied in the bending direction, if there is a step in the piston rod 3, stress concentrates on the step and is bent at the step. To try. However, when the step exists at or near the position of the piston serving as a fulcrum, the step has relatively high strength against bending, but the farther from the fulcrum position, the lower the strength against bending. . From the above, the piston rod 3 there is a stepped two stage, the most vulnerable are part of the step d _2.

The step d ₁ is for fixing the piston 2, whereas the step d ₂ is for exerting a cushion effect. Therefore, piston 2
Distance from to the step d ₂ is dependent on the cushion stroke. In order to stop smoothly at the stroke end without any impact, it is necessary to lengthen the cushion stroke to some extent. Then, the distance from the piston 2 to the step d ₂ is longer, the intensity at the time when the bending force is applied is remarkably reduced. Also, when the step d ₂ is brought closer to the piston 2, the cushion function is reduced.

As described above, if the operation of extending and contracting the hydraulic cylinder while the large load is acting on the hydraulic cylinder is repeatedly and frequently performed, the composite load of the compression / tensile load and the bending load can be reduced. action by, causing metal fatigue at the site of the step d ₂ of the step d _1, d ₂ provided 2-stage piston rod 3 of the hydraulic cylinder, cracks are generated on its surface. Then, if the operation is continued with such a crack generated, a situation may occur in which the portion is eventually broken.

From the above, if the strength of the surface at the stepped portion provided for mounting the cushion ring constituting the cushion device is partially increased, the diameter of the piston rod can be increased or the entire piston rod can be sintered. This means that the piston rod constituting the hydraulic cylinder does not have to have more strength than necessary, for example, by inserting it.

[0027]

Therefore, a feature of the structure adopted in the present invention is that a piston connected to a piston rod is slidably mounted in a cylinder, and the vicinity of a stroke end on the extension side of the piston is provided. In order to exert a cushioning effect, a cushion flow path is formed in the cylinder, and a small-diameter ring insertion portion is formed by providing a step at an intermediate position of the piston rod, and a cushion is formed in the ring insertion portion. Attach the ring in a loose fit state,
The cushion ring has a flow passage formed from the inner surface of the cushion ring to the inside of the cylinder when the cushion ring comes into contact with the piston. The quenching layer is formed.

Here, the step in the piston rod has a vertical wall, and a curved surface which is concavely curved is formed at the transition from the vertical wall to the outer peripheral surface on the smaller diameter side, and the partially quenched layer is formed from the curved surface. To be provided in the part over the vertical wall,
It is more preferable from the viewpoint of improving strength.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. The overall configuration of the hydraulic cylinder and the cushion device mounted on the hydraulic cylinder is not particularly different from that of the above-described conventional technology, so that the same or equivalent components are denoted by the same reference numerals. The description is omitted.

[0030] First, in the piston rod 3, a step D ₂ of the cushion ring 11 is formed between the ring mounting portion 3b and the rod body 3a which is mounted, in order to alleviate the change of its shape, the vertical wall V The transition portion from the to the outer peripheral surface R of the ring mounting portion 3b is not formed at a right angle, but forms a curved surface portion C having a concavely curved shape. As a result, a sharp change point is not generated in this portion, and a certain degree of stress dispersion is achieved. Here, since the vertical surface V is for the cushion ring 11 to contact and close the one-way flow path, the vertical surface V is
Has a certain width to ensure that the end faces thereof can abut, and the surface accuracy for this width is extremely high.

In addition, a partial quenching layer H is formed by partially quenching the portion of the step D ₂ over the entire circumference.
To form Here, quenching is basically performed on the curved surface portion C where the stress is most concentrated, but since the cushion ring 11 is pressed against the portion of the vertical wall V, the vertical wall V In order to improve the strength of the vertical hardening layer, the portion of the vertical wall V is also included in the partially hardened layer H.

[0032] As already described above, when the large load is to operate the hydraulic cylinder while acting, the piston rod 3, the compression, tension, site of the step D ₂ will be the load is applied in bending Stress is concentrated on Moreover,
Metal fatigue is caused by the interaction between compression and tension repeatedly and frequently. Therefore, by quenching this portion, the strength of the surface is improved, and the occurrence of surface cracks due to metal fatigue can be suppressed. Further, in order to exert no regret cushioning by the cushion ring 11, the position of the step D _2, it is necessary to have a significant distance from the connecting portion to the piston 2 of the piston rod 3.
For this reason, a large bending force acts on the step D ₂ ,
There is no fear of buckling due to the strength improvement by quenching.

The cushion ring 11 abuts on the vertical wall V at the step D _{2. During} the cushion stroke, the pressure difference between the hydraulic oil passage 8 connected to the cushion passage 12 and the rod chamber 6 in the cylinder 1 is increased. At its maximum, the cushion ring 11 is pressed very strongly against the vertical wall V. Moreover, this vertical wall V of the cushion ring 11
The surface pressed against is narrower in width because of the tapered portion 11a for attracting. When the piston rod 3 is contracted, the cushion ring 11
In order to make the escape from the cushion flow path 12 smoother, it is necessary to increase the inner diameter of the cushion ring 11 as much as possible in order to increase the flow area of the one-way flow path. The area of the contact surface to V is significantly restricted. Therefore,
Although the surface pressure per unit area increases, the vertical wall V is also partially quenched, so that there is no possibility that the cushion ring 11 is deformed or damaged due to pressing. As a result, the flow path area of the one-way flow path can be increased, so that the cushion ring 11 can escape from the cushion flow path 12 more smoothly.

As described above, when the cushion device having the cushion ring 11 is mounted on the hydraulic cylinder,
The reduction in strength due to the provision of the step D ₂ in the piston rod 3 is further reinforced by quenching, but the quenched layer H is provided only on a part of the entire length of the piston rod 3. Therefore, the length of the piston rod 3 has no effect on the range in which the quenching process is performed. Even if the entire length of the piston rod 3 is extremely long in order to increase the stroke of the hydraulic cylinder, the range in which the quenching is performed is limited. does not change. As a result, cost increase due to the partial quenching process can be suppressed to a minimum.

[0035] As described above, by performing a partial hardening, without the piston rod 3 is thick diameter, forming a ring mounting portion 3b due to the step D ₂ to some extent away from the connecting portion to its piston 2 Since the cushion ring 11 exhibiting the desired cushion characteristics can be mounted, the hydraulic excavator can also mount the cushion device on the bucket cylinder 27a whose diameter is restricted. Bucket cylinder 27a is bucket 2
In order to cut into the ground at the time of excavation by 7, an extremely strong driving force is required, and at the moment of scooping up the earth and sand, the load is suddenly canceled, so that a large compressive load and a tensile load are applied to the piston rod in a short cycle. Works. Also, when compacting the ground, the bucket 27
And repeatedly apply a shocking load. Therefore, a strong compression and pulling force acts very frequently on the piston rod of the bucket cylinder 27a, and at the same time, a very large force acts on the bending direction. Nevertheless, since the diameter of the bucket cylinder 27a is restricted, it is not possible to increase the diameter of the piston rod to improve the strength. For this reason, conventionally, it has been considered that the cushion device cannot be attached to the bucket cylinder 27a. However, since the strength of the stepped portion can be improved by performing the partial quenching, the cushion device can also be mounted on the bucket cylinder 27a, and the noise can be reduced during the operation of the excavator, and the vibration can be suppressed. The benefits are huge.

[0036]

As described above, according to the present invention, the strength of the piston rod provided for mounting the cushion ring is improved by partially quenching the step at the step. Therefore, the effect of increasing the strength of the step and maintaining the durability of the piston rod can be achieved without increasing the diameter of the piston rod more than necessary or performing particularly large heat treatment.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a piston rod showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating an entire configuration of a hydraulic cylinder.

FIG. 3 is a sectional view of a main part of a hydraulic cylinder provided with a cushion device according to a conventional technique.

FIG. 4 is an overall configuration diagram of a hydraulic shovel as an example of a machine using a hydraulic cylinder with a cushion device.

FIG. 5 is an explanatory diagram showing a force acting on a piston rod.

FIG. 6 is a stress diagram acting on two steps formed on the piston rod.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Cylinder 2 Piston 3 Piston rod 4 Bottom chamber 5 Rod chamber 7, 8 Hydraulic oil flow path 11 Cushion ring 12 Cushion flow path H Partially hardened layer C Curved surface part R Horizontal plane V Vertical wall

Claims (2)

[Claims] A piston connected to a piston rod is slidably mounted in a cylinder, and a cushion flow path is formed in the cylinder in order to exert a cushioning action near a stroke end on an extension side of the piston. A small-diameter ring insertion portion is formed by providing a step at an intermediate position of the piston rod, and a cushion ring is loosely fitted to the ring insertion portion. When abutting, a flow path communicating from the inner surface of the cushion ring to the inside of the cylinder is formed, and the piston rod has a configuration in which a partially quenched layer is formed over the entire circumference of a portion where the step is formed. A hydraulic cylinder with a cushion device. 2. A curved surface that is concavely curved is formed at a transition from the vertical wall formed by the step of the piston rod to the outer peripheral surface on the smaller diameter side, and the partially quenched layer is formed by the vertical wall from the curved surface. The hydraulic cylinder with a cushion device according to claim 1, wherein the hydraulic cylinder is formed at a portion extending to the end.