JP4041931B2 - Rod sealing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sealing device for sealing a rod of a cylinder device such as a hydraulic cylinder for adjusting a vehicle height or a hydraulic shock absorber for shock absorption.
[0002]
[Prior art]
For example, as shown in FIG. 8, a hydraulic cylinder for adjusting the vehicle height has a piston (not shown) slidably fitted in a cylinder 1 in which oil is sealed, and one end is connected to the piston. The other end of the piston rod 2 is slidably inserted through the rod guide 3 attached to the open end of the cylinder 1 and extends to the outside of the cylinder 1. The cylinder 1 is housed in a bottomed outer cylinder 4 here, and the rod guide 3 is also used as a lid for closing the annular chamber 5 between the outer cylinder 4 and the cylinder 1. The position is fixed by a lock ring 6 screwed into the opening end of 4. An oil passage (not shown) is provided in the piston rod 2, and oil is supplied / discharged from an external oil supply / discharge means (not shown) through the oil passage, and the piston is accordingly supplied. The extension length of the rod 2 changes, and the vehicle height is adjusted.
[0003]
In such a hydraulic cylinder, the piston rod 2 is generally sealed by a double seal 8 disposed in an annular groove 7 provided in the inner periphery of the rod guide 3 and an oil seal 9 disposed in the lock ring 6. It is made in two steps. The double seal 8 includes a rod seal 10 that is in sliding contact with the piston rod 2 and an O-ring 11 that elastically biases (backs up) the rod seal 10 toward the piston rod 2 side. In this case, the rod seal 10 is made of a material excellent in sliding performance with emphasis on sliding characteristics, for example, a fluororesin, and between this and the piston rod 2, the hydraulic pressure of the cylinder inner chamber 12 is reduced. In response to the rise, a slight oil leak occurs. On the other hand, the oil seal 9 is made of rubber having a good sealing property, and the oil liquid (leakage oil) leaking from between the rod seal 10 and the piston rod 2 leaks to the outside through the oil seal 9. Is prevented. On the other hand, the oil liquid from which leakage to the outside is prevented is temporarily accumulated in an oil reservoir chamber 13 formed between the double seal 8 and the oil seal 9 and then passed through an oil passage 14 provided in the rod guide 3. It escapes to the annular chamber (drain chamber) 5.
[0004]
However, in the above-described conventional general hydraulic cylinder, when the hydraulic pressure in the cylinder inner chamber 12 (high pressure side) rises above a certain value, as shown in FIG. 9, due to the differential pressure ΔP with respect to the oil reservoir chamber 13 (low pressure side). The O-ring 11 is pushed upward and is strongly pressed against the seal receiving surface 3a on the upper side (low pressure side) of the rod guide 3, the O-ring 11 is compressed and deformed, and the rod seal 10 is pressed against the piston rod 2 with a strong force. Press. As a result, the frictional resistance between the rod seal 10 and the piston rod 2 is increased, the smooth expansion and contraction of the piston rod 2 is hindered, and the riding comfort is deteriorated. In addition, the wear of the rod seal 10 is increased. As a result, there was a problem that oil leakage became severe.
In addition, in the hydraulic shock absorber, the double seal 8 composed of the rod seal 10 and the O-ring 11 is often employed, and the same problem occurs in this case. However, in the case of a hydraulic shock absorber, the annular chamber 5 around the cylinder 1 is provided as a reservoir.
[0005]
In order to solve the above problem, in Japanese Patent Laid-Open No. 10-54436, as shown in FIG. 10, an annular notch 15 is provided on the outer periphery of the front end portion of the rod seal 10 on the front side in the direction of extending the piston. 3 is divided into a main body 16 and a lid 17, and an annular projection 18 extending from the lid 17 is positioned in the notch 15. By adopting such a seal structure, when a large hydraulic pressure is applied to the O-ring 11 and a large urging force is applied to the rod seal 10, the projection 18 provided on the rod guide 3 shares the urging force, The rod seal 10 is not strongly pressed against the piston rod 2.
[0006]
By the way, the contact surface pressure distribution at the contact surface between the rod seal 10 and the piston rod 2 is ideally the contact limit point on the cylinder inner chamber 12 (FIG. 8) side, that is, the high pressure side, as shown in the right graph of FIG. It is desirable to draw a curve in which the surface pressure is maximum near A and the surface pressure is minimum near the contact limit point B on the oil reservoir 13 (FIG. 8) side, that is, the low pressure side. In other words, it is desirable that the contact pressure gradient θ ₁ on the high pressure side is larger than the contact pressure gradient θ ₂ on the low pressure side (θ ₁ > θ ₂ ). Does not occur.
[0007]
[Problems to be solved by the invention]
However, according to the new seal structure in which the annular protrusion 18 is interposed between the O ring 11 and the rod seal 10, the front end of the rod seal 10 is strongly pressed against the low pressure side seal receiving surface 3 a of the rod guide 3. As shown by a dotted line in FIG. 12, a moment in the direction of moving the front end side radially inward acts on the load seal 10, and the rod seal 10 is deformed into a state in which the diameter of the front end side is reduced. For this reason, as indicated by the dotted line in the graph on the right side of the figure, the surface pressure near the contact limit point A ′ on the high pressure side decreases, while the surface pressure near the contact limit point B ′ on the low pressure side increases, The contact surface pressure distribution is greatly deviated from the ideal curve (shown by the solid line) described above (θ ₁ <θ ₂ ), the sealing performance is reduced, and the amount of oil leakage is increased.
As shown in FIG. 13, the deformation of the rod seal 10 described above becomes more prominent when the rod seal 10 is worn (the worn portion is indicated by diagonal lines), as shown by the dotted line in the graph on the right side of the figure. The surface pressure in the vicinity of the contact limit point A ′ on the high pressure side is significantly reduced, while the surface pressure in the vicinity of the contact limit point B ′ on the low pressure side is significantly increased, and a large amount of oil leakage occurs.
[0008]
In addition, the linear expansion coefficient α ₁ of the rod seal 10 made of fluororesin is α ₁ = 100 × 10 ⁻⁶ (K ⁻¹ ), whereas the rod guide 3 is usually made of steel. The linear expansion coefficient α ₂ is α ₂ = 12 × 10 ⁻⁶ (K ⁻¹ ). When the temperature rises due to frictional heat during use or the like due to the difference in linear expansion coefficient (α ₁ −α ₂ ), as shown in FIG. 14, the step surface 10a of the rod seal 10 and the tip surface 18a of the protrusion 18 In this case, the deformation of the rod seal 10 becomes more prominent and oil leakage becomes even more severe. In addition, when the gap S is generated in this manner, the O-ring 11 bites into the gap S as shown in FIG. 15 , and the biting portion is damaged by the subsequent inclination of the rod seal 10, thereby reducing the life of the O-ring 11. It will also do.
[0009]
The present invention has been made in view of the above-described conventional problems, and the problem is that an appropriate contact surface pressure can be obtained between the rod seal and the rod, and the contact surface pressure can be reduced. It is to ensure that the maximum value always appears in the vicinity of the contact limit point on the high pressure side, thereby ensuring smooth operation of the rod and stable sealing performance.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a rod seal that slides on the rod in an annular groove formed on an inner periphery of a rod guide that slidably guides the rod, and elastically pushes the rod seal toward the rod. In the sealing device in which a double seal comprising an oscillating O-ring is arranged, an annular notch is formed on the outer periphery of the front end portion of the rod seal on the front side in the rod extending direction, and a rod guide is provided in the notch An axial depth of the notch and a length of the annular projection are set such that an annular projection extending from the position is positioned and a gap is formed between the front end of the rod seal and the seal receiving surface of the rod guide. It is characterized by setting.
[0011]
In the present invention , since the protrusion provided on the rod guide shares the urging force applied from the O-ring to the rod seal, the entire rod seal is not strongly pressed against the rod. In addition, since a gap is formed between the front end of the rod seal and the low pressure side seal receiving surface of the rod guide, a moment in the direction of moving the rear end side radially inward acts on the rod seal, and the low pressure side contact is always achieved. An ideal contact surface pressure distribution in which the surface pressure is minimum near the limit point and the surface pressure is maximum near the high pressure side contact limit point can be obtained.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
1 and 2 show a first embodiment of the present invention. Each embodiment described below is applied to the vehicle height adjusting hydraulic cylinder, and the basic structure of the hydraulic cylinder including the sealing device is the same as that shown in FIGS. Therefore, in this case, the same parts are denoted by the same reference numerals, and description thereof is omitted.
[0014]
In the first embodiment, the rod guide 3 that slides and guides the piston rod (rod) 2 extended from the piston in the cylinder 1 includes the main body 16 as described above with reference to FIG. It consists of a lid 17. The main body 16 has a stepped outer periphery, and a small diameter portion is fitted to the cylinder 1 via the seal member 20, and a large diameter portion is fitted to the outer cylinder 4 via the seal member 21. By doing so, the opening ends of the cylinder inner chamber 12 and the drain chamber 5 are liquid-tightly closed. On the other hand, the lid body 17 is pressed and fixed to the main body 16 by the lock ring 6 screwed into the outer cylinder 4. In this assembled state, the lid body 17 has a gap between the main body 16 and the lid body 17. An annular groove 7 (FIG. 1) for housing the double seal 8 is formed. Therefore, the low pressure side seal receiving surface 3a of the rod guide 3 is set to the lid 17 in the present embodiment. A bush 23 is fitted to the inner periphery of the main body 16, and the piston rod 2 is directly slid and guided by the bush 23. In addition, an orifice 24 is provided in the oil passage 14 for returning the oil liquid accumulated in the oil reservoir 13 on the oil seal 9 side to the drain chamber 5, and the orifice 24 has a predetermined inside in the oil reservoir 13. Hydraulic pressure is maintained.
[0015]
As described above, the rod seal 10 constituting the double seal 8 has the annular cutout 15 on the outer periphery of the front end portion on the low pressure side, and the rod guide 10 is inserted into the cutout 15 as described above. An annular projection 18 extending from the lid body 17 constituting 3 is disposed. Therefore, in the first embodiment, a gap is always formed between the front end of the rod seal 10 and the low pressure side seal receiving surface 3a set on the lid 17 even if the temperature rises. Further, the axial depth L ₁ of the notch 15 and the length L ₂ of the annular protrusion 18 are initially set.
[0016]
Specifically, when the linear expansion coefficient of the rod seal 10 is α ₁ , the linear expansion coefficient of the lid 17 is α ₂ , and the maximum temperature difference is ΔT, the condition (L ₂ −L ₁ ) + (L ₂ · α ₂ −L ₁ · α ₁ ) ΔT> 0
However, α ₁ > α ₂
Thus, the initial gap δ is set so as to satisfy the following condition. Thus, even after the temperature rises to the maximum, a slight gap δ ′ is provided between the lid body 17 (rod guide 3) and the rod seal 10. Will be secured.
[0017]
In the first embodiment, when an oil liquid is supplied into the cylinder 1 by a supply / discharge oil means (not shown) and the pressure in the cylinder inner chamber 12 increases, a slight gap between the rod seal 10 and the piston rod 2 is obtained. Oil leaks from the gap. When the pressure in the cylinder chamber 12 temporarily becomes high due to the load on the hydraulic cylinder, the differential pressure ΔP between the cylinder chamber 12 and the oil reservoir 13 temporarily increases, and the rod seal 10 and the piston A large amount of oil tends to leak from between the rod 2. However, in the first embodiment, a gap (δ to δ ′) is always formed between the front end of the rod seal 10 and the low pressure side seal receiving surface 3a of the lid body 17 (rod guide 3). Therefore, the rod seal 10 is subjected to a moment in the direction of moving the rear end side radially inward, so that the rod seal 10 is deformed into a state in which the rear end side is reduced in diameter as shown in FIG. For this reason, as indicated by the dotted line in the graph on the right side of the figure, the surface pressure near the contact limit point A ′ on the high pressure side increases while the surface pressure near the contact limit point B ′ on the low pressure side decreases, The contact surface pressure distribution approximates to the ideal curve (shown by a solid line) and the sealing performance is improved, and the above-described large amount of oil leakage is prevented in advance. In the first embodiment, it is assumed that the linear expansion coefficient α ₁ of the rod seal 10 is larger than the linear expansion coefficient α ₂ of the lid body 17 (α ₁ > α ₂ ). When the relationship is reversed (α ₁ ≦ α ₂ ), the initial gap δ expands as the temperature rises, so there is no concern about the aforementioned oil leakage.
[0018]
Further, the O-ring 11 is strongly pressed against the seal receiving surface 3a of the lid body 17 by the above-described differential pressure ΔP and is compressed and deformed, and the rod seal 10 tries to press the piston rod 2 with a strong force. Since the projection 18 provided on the shaft shares the urging force, the rod seal 10 is not strongly pressed against the piston rod 2, and the smooth expansion and contraction of the piston rod 2 is guaranteed. In the first embodiment, in particular, the oil passage 14 that communicates the lower oil reservoir 13 and the drain chamber 5 with the oil seal 9 is throttled by the orifice 24, so that it is stored in the oil reservoir 13. As a result, the pressure difference ΔP between the cylinder inner chamber 12 and the oil reservoir chamber 13 does not increase so much. For this reason, the urging force applied to the rod seal 10 from the O-ring 11 is further suppressed, and the smooth expansion and contraction of the piston rod 2 is more reliably ensured. In the first embodiment, the example in which the gap δ is always provided between the lid 17 (rod guide 3) and the rod seal 10 has been described. However, when the pressure in the cylinder inner chamber 12 increases. Even if the gap δ disappears, it is inferior to that always having the gap δ, but the effect can be obtained.
[0019]
FIG. 4 shows a second embodiment of the present invention. A feature of the second embodiment is that a curved surface 30 having a predetermined radius R ₁ is provided on the inner peripheral edge of the tip of the annular protrusion 18 provided on the lid body 17, and the high-pressure side contact limit portion of the rod seal 10 is provided. In addition, a curved surface 31 having a predetermined radius R ₂ is provided. By providing the curved surfaces 30 and 31 in this way, the rod seal 10 is easily deformed by reducing the diameter of the rear end side thereof, and the surface pressure near the contact decline point A on the high pressure side is further increased. The sealing performance is further improved.
[0020]
FIG. 5 shows a third embodiment of the present invention. The feature of the third embodiment is that the annular notch 15 formed in the rod seal 10 has a shallow radial depth, or the annular protrusion 18 provided on the lid 17 has a thick wall. The rod seal 10 is brought into close contact with the inner surface of the protrusion 18. In this way, by bringing the rod seal 10 into close contact with the inner surface of the protrusion 18, the moment generated in the rod seal 10 is reduced as much as possible, and stress is excessively concentrated on the high pressure side contact limit point A of the rod seal 10. The local wear that tends to occur in the vicinity thereof is suppressed, and the durability of the rod seal 10 is improved.
[0021]
6 and 7 show a fourth embodiment of the present invention. The feature of the fourth embodiment is that the front end of the rod seal 10 has an arcuate medium-high shape, and the arc surface 32 is a low pressure side seal receiving surface of the lid body 17 (rod guide 3). 3a is in line contact. By setting the front end shape of the rod seal 10 in this way, even if the front end of the rod seal 10 is pressed against the low pressure side seal receiving surface 3a due to the difference in linear expansion coefficient between the rod seal 10 and the lid body 17, FIG. As shown in FIG. 3, the amount of compressive deformation at the front end of the rod seal 10 is small, and even if a moment acts in the direction of moving the front end toward the inside of the radius, the amount is small, which is ideal as in the above embodiments. A good contact surface pressure distribution is obtained and the sealing performance is improved. The arc surface 32 at the front end of the rod seal 10 can be replaced with a convex shape.
[0022]
【The invention's effect】
As described above in detail, according to the present invention, an appropriate contact surface pressure is obtained between the rod seal and the rod, and the maximum value of the contact surface pressure always appears near the contact limit point on the high pressure side. Thus, the smooth operation of the rod and the stable sealing performance are ensured, and the reliability of the apparatus is remarkably improved.
In addition, ensuring sealing performance is handled only by changing the dimensional relationship between the rod seal and the annular protrusion provided on the rod guide, or by changing the shape of the rod seal itself, so it can be applied to mass production without increasing costs. And its utility value is great.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the structure of a rod sealing device according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a main part of a vehicle height adjusting hydraulic cylinder to which the sealing device according to the first embodiment is applied.
FIG. 3 is a schematic diagram for explaining the reason for improving the sealing performance by the sealing device.
FIG. 4 is a schematic diagram showing a second embodiment of the present invention.
FIG. 5 is a schematic diagram showing a third embodiment of the present invention.
FIG. 6 is a schematic diagram showing a fourth embodiment of the present invention.
FIG. 7 is a schematic diagram showing a deformed state of a rod seal in the fourth embodiment.
FIG. 8 is a cross-sectional view showing a general structure of a conventional sealing device and a main structure of a vehicle height adjusting hydraulic cylinder to which the conventional sealing apparatus is applied.
FIG. 9 is an enlarged sectional view of a conventional sealing device.
FIG. 10 is a cross-sectional view showing the structure of a new type of sealing device substantially the same as the sealing device of the present invention.
FIG. 11 is a schematic diagram showing an ideal contact surface pressure distribution in a new type of sealing device.
FIG. 12 is a schematic diagram for explaining an example of a failure state in a new-type sealing device.
FIG. 13 is a schematic diagram for explaining another example of a failure state in the new-type sealing device.
FIG. 14 is a schematic diagram for explaining still another example of a failure state in the new-type sealing device.
FIG. 15 is a schematic diagram for explaining still another example of a failure state in the new type sealing device.
[Explanation of symbols]
1 Cylinder 2 Rod 3 Rod guide (rod)
3a Low pressure side seal receiving surface 4 Outer cylinder 5 Drain chamber (annular chamber)
8 Double seal 7 Annular chamber 9 Oil seal 10 Rod seal 11 O-ring 13 Oil reservoir chamber 14 Oil passage 15 Notch 16 Body 17 Lid 18 Annular protrusion 32 Arc surface

Claims (1)

A rod having one end inserted into a cylinder filled with oil and the other end slidably inserted through a rod guide attached to the opening end of the cylinder, and extending out of the cylinder; and the rod A seal device that seals between a guide and a rod seal that slides on the rod in an annular groove formed on an inner periphery of the rod guide and an O-ring that elastically biases the rod seal toward the rod In the rod seal, an annular notch is formed on the outer periphery of the front end portion on the front side in the rod extending direction of the rod seal, and an annular protrusion extending from the rod guide is provided in the notch. And the axial depth of the notch and the length of the annular protrusion were set so that a gap was formed between the front end of the rod seal and the low pressure side seal receiving surface of the rod guide. Sealing device of the rod characterized by and.

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