JP2004225791A - Hydraulic cylinder and impact tester having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydraulic cylinder capable of controlling oil leakage in a simple structure and an impact tester having the hydraulic cylinder. <P>SOLUTION: A dust seal 30 is arranged closer to a tip side of a piston rod rather than a location of a U packing 20. A sliding portion 31 of the dust seal 30 receives force with a direction of increasing sealing performance of the dust seal 30 from a piston rod 12 when the piston rod is expanded. The sliding portion 31 of the dust seal 30 receives force with a direction of relieving sealing performance when the piston rod is contracted. Consequently, thickness of an oil film stuck on the piston rod 12 becomes thinner when the piston rod 12 is expanded, and the amount of oil scraped by the dust seal 30 is reduced when the piston rod 12 is contracted. Accordingly, oil leakage can be controlled. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hydraulic cylinder suitable for use in, for example, an impact tester and an impact tester having the hydraulic cylinder.
[0002]
[Prior art]
The high-speed impact tester is designed to drive a hydraulic cylinder at a high speed so that a jig of the tester collides with a test piece and breaks the test piece, and obtains an impact breaking characteristic of the test piece from data at the time of the collision (for example, see Patent Document 1). 1). A packing is provided between the cylinder tube of the hydraulic cylinder and the piston rod to prevent oil leakage, and the piston rod expands and contracts while sliding on the packing.
[0003]
[Patent Document 1]
Japanese Patent Publication No. 7-54290
[Problems to be solved by the invention]
Generally, in a hydraulic cylinder, when the piston rod slides on the packing, oil not scraped off by the packing (oil that has passed through the packing) adheres to the surface of the piston rod as an oil film. It is known that the thickness of the oil film increases as the expansion / contraction speed of the piston rod increases. In a high-speed impact tester, the piston rod is extended at a high speed in order to apply an impact to the test piece, while the return is contracted at a low speed, so the oil film thickness differs between extension and contraction. Is leaked to the outside.
[0005]
An object of the present invention is to provide a hydraulic cylinder capable of suppressing oil leakage with a simple configuration and an impact tester having the hydraulic cylinder.
[0006]
[Means for Solving the Problems]
The hydraulic cylinder according to the first aspect of the present invention includes a cylinder tube, a piston rod that expands and contracts with respect to the cylinder tube, a first seal member that closes a gap between the cylinder tube and the piston rod to prevent oil leakage, and a piston. A second seal member that has a sliding portion on which the rod slides and that is provided closer to the piston rod tip side than the first seal member, and that closes a gap between the cylinder tube and the piston rod; The sliding portion receives from the piston rod a force in the direction of increasing the sealing performance of the second seal member, and when the piston rod contracts, the sliding portion receives a force in the direction of relaxing the sealing performance of the second sealing member. 2. Determine the shape of the seal member.
According to the second aspect of the present invention, the surface of the second seal member that reaches the sliding portion is a tapered surface in which the surface on the distal end side of the piston rod forms an acute angle with respect to the direction of expansion and contraction of the piston rod, and the piston rod base end. The side surface is a tapered surface that forms an obtuse angle with respect to the direction of expansion and contraction.
An impact tester according to a third aspect of the present invention includes the above-described hydraulic cylinder and a control device that controls expansion and contraction of the hydraulic cylinder, and is configured to apply an impact to a test piece by extending the hydraulic cylinder.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment in which the present invention is applied to a hydraulic cylinder of a high-speed impact tester will be described with reference to FIGS.
First, the basic configuration of the high-speed impact tester will be described with reference to FIG. A hydraulic cylinder 10 is disposed above the support table 1 on which the test piece TP is mounted. The hydraulic cylinder 10 includes a reciprocating piston 11 that moves up and down in a cylinder tube 14 and upper and lower piston rods 12 and 13. Having. The lower piston rod 12 protrudes downward from the cylinder tube 14, and a test jig 2 is attached to a tip of the lower piston rod 12 so as to face the test piece TP. The load detector 3 detects a load applied to the test piece TP and inputs the detected load to the control device 4.
[0008]
Between the lower part of the cylinder tube 14 and the lower piston rod 12, an annular U packing (first seal member) 20 and a dust seal (second seal member) 30 made of rubber are provided. Expands and contracts while sliding on the U packing 20 and the dust seal 30. The U packing 20 seals the oil in the cylinder chamber so as not to leak outside, and the dust seal 30 originally prevents dust from entering the cylinder chamber. In the present embodiment, the dust seal 30 is also provided with an oil leakage prevention function, but details thereof will be described later.
[0009]
The upper piston rod 13 of the hydraulic cylinder 10 is inserted into, for example, a capacitance type displacement detector 5 for detecting a displacement amount of the piston 11, and a detection signal of the displacement detector 5 is input to the control device 4 as a displacement signal. . The flow rate switching valve 6 arbitrarily switches the moving speed of the piston 11, that is, the speed for impact destruction on the test piece TP in a range of, for example, 1 mm / s to 20 m / s. The accumulator 7 accumulates the discharge pressure from a hydraulic pump (not shown).
[0010]
When the test piece TP is supported on the support table 1 and the moving speed of the piston 11 is set by the flow rate switching valve 6 and oil is supplied to the upper cylinder chamber of the hydraulic cylinder 10, the piston 11 descends and the lower piston rod 12 Extend, and the test jig 2 collides with the test piece TP and destroys it. The control device 4 reads each output of the load detector 3 and the displacement detector 5 and processes these data to obtain the impact fracture characteristics and the like of the test piece.
[0011]
By the way, when the lower piston rod 12 slides on the U packing 20, the oil that has passed without being scraped off by the U packing 20 adheres to the surface of the piston rod 12 as an oil film. The thickness of the oil film varies depending on the moving speed of the piston rod 12, the viscosity of the oil, the contact pressure distribution of the U-packing 20, and the like. However, focusing on the speed, the oil film thickness is almost proportional to the square root of the piston rod speed. It turns out to be thicker.
[0012]
In the high-speed impact tester of this embodiment, the piston rod 12 is extended at a high speed (for example, a maximum of 20 m / s) in order to apply an impact force to the test piece TP, and is returned at a low speed (for example, 10 cm / s). ), The film thickness at the time of contraction is significantly smaller than that at the time of extension. This means that an amount of oil corresponding to the film thickness difference is scraped outward by the U-packing 20 during shrinkage, and the scraped oil will not leak unless other measures are taken. It flows outside.
[0013]
Therefore, in the present embodiment, the oil leak caused by the speed difference is prevented by providing the dust seal 30 on the distal end side of the piston rod with respect to the U packing 20. As can be seen from FIG. 2, in the dust seal 30, a portion indicated by reference numeral 31 contacts the surface of the piston rod 12, and the piston rod 12 slides on this portion. Of the upper and lower surfaces 32, 33 reaching the sliding portion 31, the surface 32 on the distal end side of the piston rod is a tapered surface which forms an acute angle with respect to the direction of expansion and contraction of the piston rod 12, and the surface 33 on the proximal end side of the piston rod. Is a tapered surface that forms an obtuse angle with respect to the direction of expansion and contraction.
[0014]
When the angles of the surfaces 32 and 33 are determined in this manner, the force generated in the sliding portion 31 when the piston rod 12 is extended is the force in the direction in which the sliding portion 31 is pressed against the peripheral surface of the piston rod 12, that is, the dust seal. 30 acts as a force in the direction of increasing the sealing performance. Therefore, even if the piston rod 12 is extended at a high speed, the amount of oil scraped off by the dust seal 30 is large, and the thickness of the oil film adhered to the piston rod 12 is reduced.
[0015]
On the other hand, the force generated in the sliding portion 31 when the piston rod 12 contracts acts as a force in a direction in which the sliding portion 31 moves away from the peripheral surface of the piston rod 12, that is, a force in a direction in which the sealing property of the dust seal 30 is reduced. . Therefore, even if the contraction speed of the piston rod 12 is low, the amount of oil scraped off by the dust seal 30 is small, and most of the oil passes through the dust seal 30 and returns to the cylinder tube 14 side.
[0016]
As described above, the dust seal 30 according to the present embodiment has two functions, that is, the function of reducing the thickness of the oil film when the piston rod 12 extends, and the function of reducing the scraping amount of the oil film when the piston rod 12 contracts. And a synergistic effect thereof, so that the amount of oil leakage can be reduced to a minimum.
[0017]
By the way, the dust seal used for the hydraulic cylinder has a priority to the original function of preventing dust from entering, so that it is upside down as above, that is, the tapered surface 32 forms an obtuse angle with the piston rod 12 and the surface 33 forms an acute angle. It is usually arranged in. In this arrangement, the dust seal acts in a direction that promotes the amount of oil leakage, and is not suitable when there is a speed difference in expansion and contraction as in a high-speed impact tester. In the present embodiment, by mounting the dust seal 30 upside down from normal, it is possible to minimize the amount of oil leakage even when there is a speed difference in expansion and contraction.
[0018]
Here, by mounting the dust seal 30 in the opposite manner as usual, there is a possibility that the original dust prevention effect may be slightly reduced. However, the dustproof effect is not completely impaired, and there is no problem if the impact test is performed in a clean room. Even if the dustproof effect is somewhat sacrificed, the effect of suppressing oil leakage is great.
[0019]
The second seal member is not limited to the dust seal as described above. When the piston rod is extended, the sliding portion receives a force in the direction of increasing the sealing performance from the piston rod, and when contracted, the sliding portion relaxes the sealing performance. What is necessary is just to receive the force of a direction. Although the hydraulic cylinder of the impact tester has been described as an example, the present invention can also be applied to a hydraulic cylinder used in a device other than the impact tester as long as the extension speed of the piston rod is controlled to be faster than the contraction speed. Can be applied.
[0020]
【The invention's effect】
According to the present invention, a second sealing member is provided in addition to the first sealing member for preventing oil leakage, and when the piston rod is extended, the sealing property of the second sealing member is increased, and when the piston rod is contracted, the second sealing member is provided. Since the sealing properties of the members are reduced, it is possible to minimize the amount of oil leakage even when there is a speed difference in the expansion and contraction of the piston rod. In particular, since the impact tester has a large difference in the speed of expansion and contraction of the piston rod of the hydraulic cylinder, the effect of applying the present invention is large.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a main part of a high-speed impact tester according to an embodiment of the present invention.
FIG. 2 is an enlarged view showing a seal portion of a hydraulic cylinder of the high-speed impact tester.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Support stand 2 Test jig 3 Load detector 4 Control device 5 Displacement detector 10 Hydraulic cylinder 11 Piston 12, 13 Piston rod 14 Cylinder tube 20 U packing 30 Dust seal 31 Sliding part 32 Lower surface (taper surface)
33 Top surface (tapered surface)

Claims (3)

It has a cylinder tube, a piston rod that expands and contracts with respect to the cylinder tube, a first seal member that blocks a gap between the cylinder tube and the piston rod to prevent oil leakage, and a sliding portion on which the piston rod slides. A second seal member provided closer to the distal end of the piston rod than the first seal member, and closing a gap between the cylinder tube and the piston rod. The second seal receives a force from the piston rod in a direction to increase the sealing performance of the second sealing member, and the sliding portion receives a force in a direction to ease the sealing performance of the second sealing member when the piston rod contracts. A hydraulic cylinder wherein the shape of a member is determined. The surface of the second seal member that reaches the sliding portion is a tapered surface in which the surface on the distal end side of the piston rod forms an acute angle with respect to the expansion and contraction direction of the piston rod, and the surface on the proximal end side of the piston rod is The hydraulic cylinder according to claim 1, wherein the hydraulic cylinder has a tapered surface that forms an obtuse angle with respect to the expansion and contraction direction. 3. An impact tester comprising: the hydraulic cylinder according to claim 1; and a control device for controlling expansion and contraction of the hydraulic cylinder, wherein an impact is given to the test piece by extension of the hydraulic cylinder.

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