RU2681556C2 - Hydraulic cylinder with measuring system for determining piston position and method for detecting leak through seal in hydraulic cylinder - Google Patents

Abstract

FIELD: machine building.SUBSTANCE: hydraulic cylinder is designed for reciprocating movement of the working body. Hydraulic cylinder (1) is equipped with a measuring system for determining the position of piston (2) movably mounted therein, which separates first cavity (10) of the hydraulic cylinder from second cavity (12) thereof. Hydraulic cylinder (1) has ultrasonic sensor (4), which equally can emit and receive ultrasonic waves (24, 26). For carrying out the measurement process, ultrasonic waves propagate in first cavity (10), which communicates with the atmosphere through opening (6). Method is designed to detect leakage through the sealing element of hydraulic cylinder (1), in which piston (2) is moved to a mechanically limited end position, in which the volume of first cavity (10) is maximum, and the presence of leakage through piston seal (14) is determined.EFFECT: technical result is improving the accuracy of determining the position of the piston and detect leaks.14 cl, 1 dwg

Description

The invention relates to a hydraulic cylinder with a measuring system for determining the position of a piston movably mounted in it according to the preamble of claim 1.

The invention further relates to a method for detecting leaks through a hydraulic cylinder seal according to the preamble of claim 11.

EP 1079118 A2 describes a measuring system for determining the position of a piston in a hydraulic cylinder. In such a system, the position of the piston in the hydraulic cylinder is determined using an ultrasonic sensor despite changes in the pressure and temperature of the working medium prevailing in the hydraulic cylinder, which, as you know, affects the speed of propagation of ultrasonic waves in it.

The possibility of such a determination of the position of the piston is provided through the use of a pressure sensor and a temperature sensor, which measure the pressure and temperature in the cavity into which the working medium is supplied and in which the ultrasonic sensor is also located. Based on the measured pressure and temperature, the speed with which the propagation of ultrasonic waves in the working medium under these conditions is then determined. Together with the measurement of the time that elapses from the moment of ultrasonic wave emission by an ultrasonic sensor until it receives ultrasonic waves reflected from the piston bottom, the position of the piston in the hydraulic cylinder can be determined.

The solution proposed in the above publication regarding the measuring system for determining the position of the piston requires additional components, such as a pressure sensor, in addition to the ultrasonic sensor. In addition, this solution requires high costs for calculations and measurements in order to obtain an accurate result on determining the position of the piston despite the pressure and temperature changing in the hydraulic cylinder. The method for detecting leaks through the sealing element of the hydraulic cylinder is not known from this publication.

Based on the aforementioned prior art, the present invention was based on the task of developing a hydraulic cylinder with a measuring system for determining the position of a piston that is movably mounted in it, which would make it possible to accurately determine the position of the piston despite the various pressures and temperatures prevailing in the hydraulic cylinder, and which in addition It would be inexpensive to implement and optimized for the occupied installation space.

This problem is solved using the distinguishing features presented in paragraph 1 of the claims.

Another objective of the present invention was further to provide a method for detecting leaks through the sealing element of the hydraulic cylinder, which method would allow a simple way and with high accuracy to detect such a leak through the sealing element of the hydraulic cylinder.

This problem is solved using the distinctive features presented in paragraph 11 of the claims.

The inventive hydraulic cylinder with a measuring system for determining the position of a piston movably mounted in it has a first cavity, which is primarily communicated through an opening with the atmosphere, is respectively filled with air, and a second cavity separated from it by a piston. Such a hydraulic cylinder further has an ultrasonic sensor for emitting and receiving ultrasonic waves, while determining the position of the piston using an ultrasonic sensor is possible through the first cavity of the hydraulic cylinder, in which constant pressure predominates.

An advantage of the present invention is that the propagation of ultrasonic waves to determine the position of the piston is not adversely affected by the pressure of the working medium, such as, for example, oil-based working fluid or compressed air, since according to the invention the position of the piston is determined through the first cavity of the hydraulic cylinder, which communicates through a hole with the atmosphere and in which therefore mainly constant pressure prevails.

According to the present invention, the emission of ultrasonic waves is possible in such a way that they propagate in the first cavity of the hydraulic cylinder in the direction of the piston.

A related advantage is that due to the tubular geometry of the hydraulic cylinder, respectively, of the first cavity, the ultrasonic waves are focused, due to which, despite the use of a relatively low-power ultrasonic sensor, high-precision measurement of even large distances is possible.

According to the invention, the ultrasonic sensor may be located in the bottom of the first cavity. In this regard, the ultrasonic sensor can be primarily arranged in such a way that, with its longitudinal axis, it is at least approximately located on the axis of symmetry of the piston. In another preferred embodiment, the ultrasonic sensor can be oriented with its radiating surface approximately perpendicular to the axis of symmetry of the piston in order to minimize unwanted reflections from the inner walls of the hydraulic cylinder.

Depending on the design of the hydraulic cylinder and / or other requirements, the longitudinal axis of the ultrasonic sensor can also be crossed with the axis of symmetry of the piston, positioned at an angle to it, or arranged with a parallel displacement relative to it. An ultrasonic sensor may also be located in the wall of the hydraulic cylinder.

The advantage associated with the placement of the ultrasonic sensor in the first cavity is its protection from the influence of external factors, for example, from atmospheric factors, as well as from pollution.

An advantage of the measuring system according to the invention for determining the position of the piston is that it is possible in a simple way to efficiently detect a leak through the piston seal and / or its stem seal.

To further improve the measurement accuracy, a temperature sensor according to the invention can be provided with a temperature sensor for measuring air temperature in the first cavity. The presence of such a temperature sensor makes it possible to take into account changes or differences in the speed of propagation of ultrasonic waves caused by changes in temperature in the first cavity. Such a temperature sensor may be located in the bottom of the first cavity or in the wall of the hydraulic cylinder.

To reduce the size of the measuring system, a temperature sensor may preferably be integrated into the ultrasonic sensor.

According to the invention, a computing device can be provided which calculates the position of the piston based on the time period elapsed from the moment of emission of ultrasonic waves to the moment of receiving ultrasonic waves reflected from the piston.

According to the present invention, the hydraulic cylinder may be a differential cylinder, in which the piston rod passes through the second cavity, and such a hydraulic cylinder is mainly hydraulically loaded only from the piston rod side.

According to the invention, for moving suspended loads, the hydraulic cylinder can be oriented substantially vertically. In this case, the piston rod in the preferred embodiment can be oriented approximately in the direction of gravity in order to first of all minimize, respectively eliminate the one-sided load on the inner cylinder walls from the piston side, and thereby on the piston seal, its piston rod and this rod seal .

In the implementation of the proposed invention, a method for detecting primarily due to damage and / or wear of a leak through at least one sealing element of the hydraulic cylinder, the following stages are performed.

The piston is moved to a mechanically limited end position in which the volume of the first cavity is maximum. Such a mechanically limited end position always serves as the same control position of the piston in the hydraulic cylinder and therefore can also serve to verify the correct operation of the ultrasonic sensor if a leak is clearly excluded.

Then determine the position of the piston, primarily with the help proposed in the invention of the computing device.

After that, the actually determined position of the piston is compared with its initial position. This initial position of the piston in the preferred embodiment is determined with guaranteed correct operation of the piston seal and the seal of its rod, while previously it was confirmed that the hydraulic cylinder and the rest met all the requirements for it regarding its tightness.

In addition to this, or alternatively, instead, then the second cavity is filled with a working medium, first of all, through the connecting element for connecting the hydraulic line leading to this second cavity, the second cavity is closed, first of all, the hydraulic line connected to it, for example, using a seat valve, and the position is determined piston for a given period of time.

In the case where, according to the present invention, when comparing the actually determined position of the piston with its initially determined position, a mismatch between these positions is revealed, based on this, it can be concluded that there is a leak through the piston seal. Since when the piston seal is leaking, the working medium, for example, oil-based working fluid (primarily hydraulic oil or unrefined oil), primarily with the piston rod oriented approximately in the direction of gravity, is on its side facing the first cavity, such a working fluid leaked through the seal fluid changes, respectively, distorts the measurement result. In this case, the emitted ultrasonic waves will be reflected already from the boundary surface of the working medium accumulated on the piston, and not only and not so much from the piston, i.e. the piston will appear to be closer to the bottom of the hydraulic cylinder; accordingly, the hydraulic cylinder will appear shorter.

In a preferred embodiment, by attaching a load, such as drill rods, to the piston rod of the hydraulic cylinder to create increased pressure in the second cavity. Due to this, even the smallest leaks can be detected in a short time when checking the piston seal and / or its stem seal.

According to the invention, the presence of a leak through the piston seal and / or its stem seal can be detected if the position of the piston changes over a predetermined period of time.

In a preferred embodiment, the method for detecting leaks can be carried out at regular intervals, which in this case also allows you to determine the magnitude of the leak in time.

The invention is described in more detail below by the example of one of its preferred embodiments with reference to the only drawing attached to the description, which schematically shows in section a hydraulic cylinder according to the invention.

The accompanying description of the drawing in section shows the proposed in the invention of the hydraulic cylinder 1, suitable for use as a drive oilfield pump.

In the hydraulic cylinder 1, its piston 2 is movably mounted, which divides the internal space of the hydraulic cylinder 1 into the first cavity 10 and the second cavity 12. The first cavity 10 is a cavity that communicates through the hole 6 with the atmosphere, and therefore cannot in this first cavity 1 neither high nor low pressure is created and therefore, ambient pressure always prevails in it. The hole 6 in this embodiment is located on the side wall of the hydraulic cylinder 1 near its bottom 8, however, it could also be located, for example, in the bottom 8.

The first cavity 10 of the hydraulic cylinder 1 from the front side is limited by its bottom 8, on which an ultrasonic sensor is provided for emitting and receiving ultrasonic waves 24, 26. As shown in the drawing, the ultrasonic waves 24 are emitted in such a way that they propagate in the first cavity 10 of the hydraulic cylinder 1 in the direction of its piston 2. In this embodiment, the ultrasonic sensor 4 has a cylindrical shape and is located in the bottom 8 of the first cavity 10, namely, in such a way that the ultrasonic sensor 4, with its axis of symmetry, is located on the axis of symmetry 28 the piston 2, and its emitting surface is oriented parallel to the piston 2 in order to minimize unwanted reflections from the inner walls of the hydraulic cylinder 1. When using an ultrasonic sensor 4, which does not have a symmetry axis, such an ultrasonic sensor 4 is preferably oriented with its longitudinal axis, which preferably passes through the center of its radiating surface, along the axis of symmetry 28 of the piston 2.

The hydraulic cylinder 1, which in this embodiment is made in the form of a differential cylinder, the piston rod 18 of it 2 passes from it through the second cavity 12, while the piston 2 of the hydraulic cylinder 1 is hydraulically loaded with the working medium only from the side of its rod 18, i.e. in the second cavity 12. Depending on the application conditions, and accordingly on the purpose, it is also possible to use a synchronous cylinder (a double-acting cylinder with a two-sided rod), which in this case, due to the presence of a second rod passing through the first cavity 10, obviously, the coordination of the location of the ultrasonic sensor 4. In this case, only the second cavity 12 would also be hydraulically loaded with the working medium. Thus, depending on the design of the hydraulic cylinder 1 and other requirements th may also be provided for the displacement of both axes of symmetry relative to each other. The ultrasonic sensor 4 may also be located in the wall of the hydraulic cylinder 1.

The hydraulic cylinder 1 according to the invention has a connecting element 20 for supplying the working medium to the second cavity 12 and for removing the working medium from it, for connecting the corresponding hydraulic line 22. As the working medium, for example, an oil-based working fluid (oil) is used, primarily hydraulic oil (hydraulic fluid) and crude oil. To move suspended loads, the hydraulic cylinder 1 is oriented generally vertically, while the piston rod 18 in the preferred embodiment is oriented approximately in the direction of gravity with the aim, first of all, of minimizing and eliminating the one-sided load on the inner walls of the cylinder from the side of the piston 2, and thereby on the piston seal 14, on its piston rod 18 and on the piston seal 16.

To measure the air temperature in the first cavity 10, a temperature sensor not shown in the drawing may be provided. It serves to further increase the accuracy of measurement, since the presence of such a sensor also allows you to take into account changes or differences in the propagation velocity of ultrasonic waves 24, 26 caused by changes in temperature in the first cavity 10. To simplify the measuring system, the temperature sensor can be integrated into the ultrasonic sensor 4.

The hydraulic cylinder 1 according to the invention further provides a computing device, not shown in the drawing, for calculating the position of the piston 2 on the basis of the time interval from the moment of emission of ultrasonic waves 24 to the moment of receiving ultrasonic waves reflected from piston 2 26. Such a computing device may be part of a measuring system and thus can be permanently connected primarily with an ultrasonic sensor 4 and / or with a temperature sensor, or primarily due to lack of space be provided externally in the form of a separate unit, which in this case is made to be connected, as necessary, primarily with an ultrasonic sensor 4 and / or with a temperature sensor.

In the inventive hydraulic cylinder 1, first of all, due to its construction shown in the drawing, it is possible to detect leakage through the seal 14 of this piston and / or through the seal 16 of its rod using a measuring system for determining the position of the piston 2.

To detect leaks through one or another sealing element of the hydraulic cylinder 1 according to the invention, the following steps are carried out.

First, the piston 2 is moved to a mechanically limited end position in which the volume of the first cavity 10 is maximum. Such a mechanically limited end position serves as an invariable control position of the piston 2 in the hydraulic cylinder 1, and in the preferred embodiment also serves to verify the correct operation of the ultrasonic sensor 4, if a leak is unambiguously ruled out, since the position of the piston determined in this end position should always be one and the same.

The (actual) position of the piston is then determined, preferably with the aid of a computing device according to the invention. To increase accuracy, the values measured by the temperature sensor can be taken into account when determining the position of the piston.

In addition to the indicated steps, the virtually determined position of the piston is then compared with its initial position.

These stages are primarily intended to detect leaks through the piston seal 14.

If there is a leak through the piston seal 14, a working medium, for example, an oil-based working fluid, primarily hydraulic oil or crude oil, will accumulate on the piston 2. Since in this case the emitted ultrasonic waves 24 will first reach this working medium and be reflected from its boundary layer, and not only and not so much from the piston 2, this leaked working fluid will change the measurement result, i.e. the piston 2 will seem to be located closer to the bottom of the hydraulic cylinder, respectively, the hydraulic cylinder will seem shorter.

In addition to the above steps, or optionally, instead of them, the following steps are then performed to detect leakage through the piston seal 14 and / or through the stem seal 16.

The second cavity 12, through the connecting element 20 leading to it, for connecting the hydraulic line 22 is filled with a working medium, the hydraulic line 22 connected to the second cavity 12 is closed and the position of the piston is determined over a predetermined period of time.

In the case where, according to the present invention, when comparing the actually determined position of the piston with its initial position, a mismatch between these positions is detected, on the basis of this, it is possible to detect the presence of a leak through the piston seal.

In the preferred embodiment, by attaching the load to the piston rod 18 of the hydraulic cylinder 1, the pressure in the second cavity 12 can be increased. Due to this, even the smallest leaks can be detected in a short time when checking the piston seal 14 and / or its rod seal 18.

According to the invention, leakage through the piston seal and / or its stem seal 16 can be detected if the position of the piston changes over a predetermined period of time, i.e. shifts towards the second cavity 12.

In a preferred embodiment, the above-described method for detecting leaks can be carried out at regular intervals, which in this case also allows you to determine the amount of leakage in time.

The invention thus provides a hydraulic cylinder equipped with a measuring system for determining the position of a piston movably mounted therein. This piston separates the first cavity of the hydraulic cylinder from its second cavity. The hydraulic cylinder according to the invention further has an ultrasonic sensor with which ultrasonic waves can be emitted and received equally. To conduct the measurement process, ultrasonic waves propagate in the first cavity, which through the hole communicates with the atmosphere.

List of Reference Items

1 hydraulic cylinder

2 piston

4 ultrasonic sensor

6 hole

8 bottom

10 first cavity

12 second cavity

14 piston seal

16 piston rod seal

18 piston rod

20 connecting element (pipe)

22 hydraulic line

24 emitted ultrasonic waves

26 reflected ultrasonic waves

28 axis of symmetry

Claims (14)

1. A hydraulic cylinder with a measuring system for determining the position of a piston (2) movably mounted in it, having a first cavity (10) and a second cavity (12) separated by a piston (2) and an ultrasonic sensor (4) for emitting and receiving ultrasonic waves ( 24, 26), characterized in that mainly constant pressure prevails in the first cavity, and the determination of the position of the piston (2) using an ultrasonic sensor (4) is possible through the first cavity (10) of the hydraulic cylinder (1). 2. The hydraulic cylinder according to claim 1, characterized in that the first cavity (10) communicates through the hole (6) with the atmosphere. 3. The hydraulic cylinder according to claim 1, characterized in that the emission of ultrasonic waves (24) is possible in such a way that they propagate in the first cavity (10) of the hydraulic cylinder (1) in the direction of the piston (2). 4. The hydraulic cylinder according to claim 1, characterized in that the ultrasonic sensor (4) is located in the bottom (8) of the first cavity (10). 5. The hydraulic cylinder according to claim 1, characterized in that using a measuring system to determine the position of the piston, leakage can be detected through the seal (14) of the piston and / or the seal (16) of its rod. 6. The hydraulic cylinder according to claim 2, characterized in that a temperature sensor is provided for measuring air temperature in the first cavity (10). 7. The hydraulic cylinder according to claim 6, characterized in that the temperature sensor is integrated in the ultrasonic sensor (4). 8. The hydraulic cylinder according to one of paragraphs. 1-7, characterized in that a computing device is provided for calculating the position of the piston (2) based on the period of time elapsing from the moment of emission of ultrasonic waves (24) to the moment of receiving ultrasonic waves reflected from the piston (2) (26). 9. The hydraulic cylinder according to claim 1, characterized in that it is a differential cylinder (1), in which the piston rod (18) of it passes through the second cavity (12). 10. The hydraulic cylinder according to claim 1, characterized in that it is oriented vertically for moving suspended loads. 11. A method for detecting leaks through the sealing element of the hydraulic cylinder (1) according to one of paragraphs. 1-10, characterized in that the piston (2) is moved to a mechanically limited end position in which the volume of the first cavity (10) is maximum, the position of the piston is determined and the actually determined position of the piston is compared with its initial position, and / or the second cavity (12 ) through the connecting element (20) leading to it, for connecting the hydraulic line (22), fill the working medium, close the hydraulic line (22) connected to the second cavity (12) and determine the position of the piston for a given period of time. 12. The method according to p. 11, characterized in that the presence of leakage through the seal (14) of the piston is ascertained if, when comparing the actually determined position of the piston with its initial position, a mismatch between these positions is revealed. 13. The method according to p. 11, characterized in that the load is attached to the piston rod (18) of the hydraulic cylinder (1). 14. The method according to one of paragraphs. 11-13, characterized in that the presence of leakage through the seal (14) of the piston and / or the seal (16) of its rod is ascertained if the position of the piston changes over a predetermined period of time.

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