The invention concerns a hydropneumatic piston accumulator, comprising an accumulator housing that defines a longitudinal housing axis. A piston is longitudinally moveable between two opposite housing covers in the housing and separates inside the housing a working chamber for a compressible medium, such as a process gas, from a working chamber for an incompressible medium, such as hydraulic fluid. A piston part of a displacement measurement device continuously acquires the respective position of the piston inside the housing.
Hydraulic accumulators, such as hydropneumatic piston accumulators, are used in hydraulic systems for the purpose of absorbing a certain volume of pressurised fluid, such as hydraulic oil, and to release it again to the system when required. In hydropneumatic piston accumulators commonly used today, the piston separates the oil-side working chamber from the working chamber filled with a process gas, such as N2. The position of the piston changes so that the accumulator absorbs hydraulic oil when the pressure increases and compresses the gas in the other working chamber. As the pressure drops, the compressed gas expands and pushes the accumulated hydraulic oil back into the hydraulic circuit. As a result of the changing volumes in the working chambers during operation, the piston performs a corresponding axial movement.
In order for the accumulator to reliably operate as required, a prerequisite is that the pressure in the working chamber for the process gas is matched to the level of pressure present in the oil-side working chamber, so that the piston inside the accumulator housing is located in suitable positions and is then able to carry out the working movements between the end-positions of the piston inside the accumulator housing. The acquisition of the position that the piston assumes in the oil-side working chamber at a given fluid pressure makes it also possible to acquire the pressure level of the process gas in the respective working chamber and enables the monitoring of the piston accumulator with respect to its correct functionality.
Different solutions have been proposed for acquiring the position of the piston. For example, DE 10 2013 009 614 A1 discloses an ultrasonic displacement measuring system in which an ultrasonic sensor is used to determine the distance from the housing cover that adjoins the working chamber that contains the process gas to the side of the piston facing that housing cover. This solution is complicated since the measuring results of the acoustic logging require continuous error correction due to changes in the sound propagation speed in the gas-filled working chamber during operation. In a further known solution, which is disclosed in DE 103 10 427 A1, a series of magnetic field sensors is arranged on the outside along the accumulator housing, which sensors react to the field of a magnet arrangement that is disposed on the piston of the piston accumulator. This solution has the disadvantage that a magnetic strip containing the magnetic field sensors must be attached to the outside of the accumulator housing.
Based upon the described prior art, an object of the invention is to provide a hydropneumatic piston accumulator of the kind described at the outset, which has an improved displacement measuring device that makes the acquisition of the piston position possible in a particularly simple and advantageous manner.
According to the invention, this object is basically met by a piston accumulator having, as a significant feature of the invention, a stationary, rod-shaped guide disposed in the accumulator housing. The guide passes all the way through the piston in each of its displacement positions inside the accumulator housing guides the piston until the respective end stop at one of the two housing covers. The piston is sealed with respect to the guide through a sealing means. The reliable internal guidance of the piston, which, according to the invention, is provided through the rod-shaped guidance of the piston, ensures a more reliable and more accurate acquisition of measurements, while utilising different kinds of measuring methods known from prior art. At the same time the sealing means formed between piston and the rod-shaped guide, which creates a reliable separation of the media in the working chambers, provides a particularly reliable operational function of the piston accumulator also during the measurement acquisition process.
Advantageous displacement measuring devices that may be used are optical measuring systems such as laser measuring systems, acoustic measuring systems such as an ultrasonic measuring system such as a magnetic measuring system, and inductive measuring system, such as a Hall sensor measuring system or a magnetostrictive measuring system. A corresponding laser measuring system may be applied as is described in the documents DE 10 2011 007 765 A1 or DE 10 2014 105 154 A1. A system using an ultrasonic measuring device may be used as is described in document DE 10 2013 009 614 A1.
In particularly advantageous exemplary embodiments, the rod-shaped guide inside the accumulator housing may at least partially be made in form of a hollow rod and may house further components of the displacement measuring device, such as a waveguide of a magnetostrictive measuring system or a chain of Hall sensors of a sensor measuring system. Alternatively, the piston guide may be formed directly from further parts of the respective displacement measuring device, such as the waveguide of the magnetostrictive measuring system. Designing the rod-shaped guide as a hollow rod is particularly advantageous when utilising optical and acoustic measuring systems since the inside of the hollow rod provides a space for transmitted and reflected optical or acoustic radiation that is separated from the working chambers. Since in this instance the propagation velocity is not influenced by conditions such as pressure and temperature, as would be the case for the propagation of free ultrasonic waves or free laser radiation through media with changing sound velocity or optical permeability, the measuring result is not influenced by changing media states as is the case in the prior art described earlier.
For the rod-shaped guide, such as the hollow rod, a lead-through with a permanent magnet device may preferably be provided in the piston that extends coaxially to the longitudinal axis. The permanent magnet device may act as position encoder in a Hall sensor measuring system, as well as in a magnetostrictive measuring system.
In a magnetostrictive measuring system the rod-shaped guide may be formed through an electrically non-conductive jacket element that directly surrounds the instrument wire. In that jacket element, which may for example be made from a synthetic material, an electrical return conductor may also be embedded to conduct the current pulse that triggers the measuring process. The electrical return conductor is covered by a further protective layer that forms the outside of the round strand, which forms the rod-shaped guide.
In particularly advantageous exemplary embodiments, the hollow rod that forms the rod-shaped guide is preferably made from a preferably pressure-resistant, circular cladding tube. The cladding tube is preferably made from a non-magnetic, metallic material. The smooth outer surface facilitates the provision of a smooth-running guide through the piston in its displacement movements.
A particularly advantageous design may be in which the accumulator housing is provided with a cylindrical tube, which is closed at both ends by a housing cover. The cladding tube is attached with at least one open end to one of the housing covers. A pulse converter with a pulse transmitter/receiver, which is connected to the waveguide of the magnetostrictive measuring system, is disposed on that one of the housing covers.
In an ultrasonic measuring system, it is possible to movably guide a position encoder inside the cladding tube, which encoder follows the piston movements due to the magnetic force of the permanent magnet device that acts between the position encoder and the piston. A transmitter/receiver of the displacement measuring device is disposed on one of the housing covers, which transmits through the respective open end of the cladding tube measuring radiation to the position encoder and receives reflected radiation from it. Since through the cladding tube a space that is separated from the media in the working chambers of the piston accumulator is available for the measuring radiation, interference in the measuring result caused in the prior art by condition changes in the media is no longer applicable. This advantage is still applicable even when a laser measuring system is used because, in contrast to the prior art, a kind of condensate (mist) can form when severe, dynamic temperature changes occur. The mist influences the laser measurement. In contrast, an undisturbed space for the measuring radiation is available in the invention.
The cover that receives the open end of the cladding tube advantageously adjoins the gas-end working chamber. This cover offers the advantage that the pulse converter of the respective sensor system can also be disposed on the housing cover of the gas-end working chamber that receives the open end of the cladding tube. The opposite housing cover then remains free for the pipe connections to the associated hydraulic system (not shown). Alternatively, the cladding tube may also be open at its unattached, free end or it may be closed at its unattached, free end. In the latter instance, pressure equalisation between the inside of the tube and the working chamber may take place at the free end of the tube so that no great demands are placed on the pressure-resistance of the cladding tube. In the second instance, where the cladding tube is closed at its free end, the inside of the tube may have no pressure applied so that the mounting provided for the pulse converter on the housing cover with its passage through to the inner space of the tube does not require any special seal.
Alternatively, it is possible to attach the cladding tube at both open ends to a housing cover each.
This design provides the advantageous option that, starting from both open ends of the cladding tube, the waveguide of each sensor system extends along part of the length of the measuring distance inside the cladding tube. This structure provides the opportunity to cover the entire measuring distance with two shorter sensor systems in instances where very long piston accumulators are used.
In further alternative exemplary embodiments, the cover that retains the open end of the cladding tube may adjoin the oil-side working chamber. The hydraulic oil connection may in this instance be disposed, axially offset, on the cover beside the centrally arranged mounting for the pulse converter of the sensor system.
In an advantageous manner, the respective sensor system may be designed as a component that is removable from an open end of the cladding tube, which has a preferably rollable, flexible jacket that envelopes the waveguide like a tube. Thus, one and the same magnetostrictive sensor system may be used for monitoring multiple piston accumulators. The sensor system only remains in the respective piston accumulator for a certain measuring period and, when completed, is removed from the piston accumulator.
Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the drawings, discloses preferred embodiments of the present invention.
Referring to the drawings that form a part of this disclosure:
The invention will now be explained by way of examples depicted in
The exemplary embodiments of the piston accumulator according to the invention shown in the drawings comprise an accumulator housing 1, which in all the exemplary embodiments shown has a cylindrical pipe 3 as a main part that forms a round, hollow cylinder. The cylindrical pipe 3 is tightly closed at both ends by screwed-in housing covers 5 and 7, between which a piston 9 is freely moveable along the longitudinal housing axis 11. The piston 9 separates a gas-side working chamber 13, which is filled to a certain filling pressure with a process gas, such as N2, as a compressible medium, from a working chamber 15, which is filled with an incompressible medium, such as hydraulic oil. To connect said working chamber 15 to an associated hydraulic system (not shown), a connecting port 17 is disposed coaxial to the longitudinal axis 11 in the housing cover 7 that adjoins the oil-side working chamber 15. At the opposite housing cover 5, which adjoins the gas-side working chamber 13, a filling passage 19 is provided, offset from the longitudinal axis 11, at the outer end of which a fill valve 21 of the usual kind is disposed, through which a certain quantity of process gas may be introduced into the working chamber 13 under a certain filling pressure.
A sensor port 23 is provided, arranged coaxial to the longitudinal axis 11, in the housing cover 5 that adjoins the gas-side working chamber 13. The sensor port 23 is provided at the outer end section with a seat for a screw connector of the pulse converter 26, as well as a passage 27, through which the strand 29 of the jacket elements of the waveguide extends along the longitudinal axis 11 and through a lead-through 31 provided in piston 9 and along the length of the measuring distance in the direction of the other housing cover 7. In this first exemplary embodiment according to the invention, the strand 29 forms the strand-shaped internal guide for the separating piston 9.
The annular body 45, which is attached inside the expansion 53, forms the support for the permanent magnet device that serves as position encoder. The permanent magnet device is formed by a magnetic ring 55, which is attached by adhesive to the free surface of the annular body 45, which free surface is flush with the bottom 43. The internal diameter of the magnetic ring 55, which is disposed coaxially to through-hole 51, is marginally larger than the diameter of through-hole 51. In order to magnetically decouple the magnetic ring 55 from the metallic piston 9, the screws 47 and the annular body 45 are made from a thermosetting synthetic material.
The third exemplary embodiment depicted in
The design in the seventh exemplary embodiment shown in
In the eighth exemplary embodiment of
The stepped through-hole 61 of housing cover 7, which retains the end 60 of the cladding tube 57, is also provided with a circular-cylindrical expansion 54, in the same manner as for through-hole 51 at the lead-through 31 of piston 9. The same annular body 45 is used for the lead-through 31 of piston 9, is provided in form of a plastic body, and is retained and secured with screws 47. The annular body 45 forms on housing cover 7 a suitable retainer for the inserted end section of the cladding tube 57. For the ultrasonic measuring method the displacement measuring device is provided with a transmitter/receiver 75 for which the outer, expanded through-hole section 67 of through-hole 61 in the oil-side housing cover 7 forms a seat. An ultrasonic transducer with a disk-shaped piezoelectric ceramic 78 extends from the through-hole section 67 into the end section of tube 57 to ascertain the distance to the reflective surface on the facing disk 58 of the position encoder. Alternatively, it would be possible to dispose the transmitter/receiver 75 on the gas-side housing cover 5, wherein the expanded through-hole section 73 at the end of the passage 27 could form the seat for the displacement measuring device.
Instead of an ultrasonic transmitter/receiver 75, a laser radiation may be used. The position encoder is then preferably provided at its upper end with a reflective surface suitable for laser light, which reflects the laser radiation emitted by the transmitter 75 to the receiver 75. From the elapsed time differences, it is then possible to determine the position of piston 9 and, if applicable, its displacement velocity and/or the acceleration values when accelerating and decelerating. Moreover, it is also possible to insert into the rod-shaped guide in form of the hollow tube or cladding tube 57 the sensor chain of a Hall sensor measuring system, for example as described in DE 10 2013 014 282 A1, instead of a magnetostrictive conductor in form of a strand 29.
It is also possible to house parts of a magnetic or inductive measuring system, as described in DE 103 10 427 A1 and DE 10 2011 090 050 A1, in the pressure-resistant, rod-shaped guide in form of the hollow tube or cladding tube 57.
In the position measurement to be carried out, the piston 9 constitutes an important component in the overall measuring system and carries parts of the same or drags them along via magnetic coupling when it moves. Moreover, the hollow guide rod 57 also houses parts of the overall measuring system, as described. In the exemplary embodiments shown, the rod-shaped guide is disposed coaxial to the longitudinal axis 11 inside accumulator housing 1. Nevertheless, it is also possible to arrange the guide, which passes through piston 9, offset from the center and parallel to the longitudinal axis 11 inside accumulator housing 1. It is, moreover, conceivable to dispose multiple guide rods parallel to each other inside accumulator housing 1. Depending on the number of guide rods used, the separating piston 9 requires the corresponding number of passages for the respective guides. Furthermore, each respective guide rod passes through the inside of the accumulator housing 1 between its two housing covers 5, 7 and is also disposed coaxial to accumulator housing 1.
The sealing means or seals 49, 50 between guide rod and piston 9 is effective in every displacement position of the piston 9. The two sealing rings that are retained in annular grooves 49, 50 surround and are in contact with the guide rod. The two sealing rings retained in the annular grooves 49, 50 are at a predeterminable axial distance in the direction of the longitudinal axis 11. As part of the internal guidance of the piston 9, the seals stabilise its axial displacement movement along the guide rod 29, 57. The sealing means 49, 50 is disposed on the inside of the piston 9. When viewing the drawing, the seals above the annular body 45 that is screw-fastened into the piston 9. The internal guidance of the piston 9 through the sealing means 49, 50 in conjunction with the outer guidance along the inner wall of the accumulator housing 1 with the respective outer sealing means 33, 35 result in an accurate displacement movement of the piston 9 inside the accumulator housing 1, which leads to improved measuring results when detecting the position of piston 9 and its actual movement states.
While various embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the claims.
Number | Date | Country | Kind |
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102016007798.0 | Jun 2016 | DE | national |
102016007824.3 | Jun 2016 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2017/000705 | 6/19/2017 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2017/220196 | 12/28/2017 | WO | A |
Number | Name | Date | Kind |
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2800924 | Antrim, Jr. | Jul 1957 | A |
3043340 | Rehbock | Jul 1962 | A |
3454050 | Wolf | Jul 1969 | A |
4876945 | Stoll | Oct 1989 | A |
5367944 | Akeel | Nov 1994 | A |
6412476 | Thompson | Jul 2002 | B1 |
7234490 | Dorr | Jun 2007 | B2 |
7270318 | Lundahl | Sep 2007 | B2 |
20140261828 | Condon | Sep 2014 | A1 |
20190120257 | Mannebach | Apr 2019 | A1 |
Number | Date | Country |
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71 03 342 | Jan 1971 | DE |
103 10 427 | Sep 2004 | DE |
10 2011 007 765 | Oct 2012 | DE |
10 2011 090 050 | Jul 2013 | DE |
10 2012 022 871 | May 2014 | DE |
10 2013 009 614 | Dec 2014 | DE |
10 2013 014 282 | Jun 2015 | DE |
10 2014 105 154 | Oct 2015 | DE |
60-143901 | Sep 1985 | JP |
61-123201 | Aug 1986 | JP |
62-97307 | Jun 1987 | JP |
7-269503 | Oct 1995 | JP |
Entry |
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International Search Report (ISR) dated Sep. 22, 2017 in International (PCT) Application No. PCT/EP2017/000705. |
Number | Date | Country | |
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20200309158 A1 | Oct 2020 | US |