HYDROPNEUMATIC PISTON ACCUMULATOR

Description

[0001] The invention relates to a hydropneumatic piston accumulator having the features in the preamble of claim 1.

[0002] Hydraulic accumulators, such as hydropneumatic piston accumulators, are used in hydraulic systems to hold specific volumes of pressurised fluid, such as hydraulic oil, and return it to the system when required. In today's common hydropneumatic piston accumulators, in which the piston separates the oil-side working chamber from the working chamber containing a working gas, such as N2, the position of the piston changes so that when the pressure rises the accumulator holds hydraulic oil, whereby the gas in the other working chamber is compressed. When the pressure drops, the compressed gas expands and displaces stored hydraulic oil back into the hydraulic circuit. The resulting changes in the volumes of the working chambers during operation result in a corresponding axial movement of the piston.

[0003] For the desired, flawless operating behavior of the accumulator, it is necessary that the pressure prevailing in the working gas chamber is adjusted to the pressure level in the oil-side working chamber, so that the piston is located at suitable points within the accumulator housing and can thus perform the working movements between the piston end positions in the accumulator housing. Determining the position assumed by the piston at a given fluid pressure in the oil-side working chamber also makes it possible to determine the filling pressure of the working gas in the corresponding working chamber and thus monitor the piston accumulator for proper functioning.

[0004] Various solutions have been proposed for determining the position of the piston. For example, document DE 10 2013 009 614 A1 discloses an ultrasonic displacement measuring system in which, starting from the housing cover adjacent to the working chamber containing the working gas, the distance to the facing side of the piston is determined using an ultrasonic sensor. This solution is complex in that, due to the changing sound propagation speed in the working chamber containing the gas during operation, continuous error correction of the measurement result obtained from a transit time determination must be carried out. In another known solution, disclosed in DE 103 10 427 A1, magnetic field sensors are arranged along a row on the outside of the accumulator housing. These sensors respond to the field of a magnet arrangement located on the piston of the piston accumulator.This solution leaves something to be desired in that a magnetic strip containing the magnetic field sensors has to be attached to the storage housing as an external component.

[0005] JP H07-269503 A describes a hydropneumatic piston accumulator, with an accumulator housing which has a cylinder tube defining a longitudinal axis, which is closed at both ends by a housing cover and in which a piston is longitudinally movable, which separates in the housing a working chamber for a compressible medium, such as a working gas, from a working chamber for an incompressible medium, such as hydraulic oil, and with a position measuring device which determines the position of the piston in the housing without contact, wherein the position measuring device has a non-magnetic measuring tube which extends through a passage formed in the piston along the longitudinal axis from one housing cover to the other housing cover and is sealed against the interior of the housing.

[0006] Further piston accumulators are described in JP S62-97307 U, DE 71 03 342 U and DE 10 2013 009 614 A1.

[0007] A distance measuring device is disclosed in DE 10 2004 057 769 A1.

[0008] Based on this prior art, the invention aims to provide a hydropneumatic piston accumulator of the type mentioned at the outset, the displacement measuring device of which enables particularly precise determination of the position of the piston in a particularly simple and advantageous manner.

[0009] According to the invention, this object is achieved by a piston accumulator which has the features of patent claim 1 in its entirety.

[0010] According to the characterizing part of claim 1, a position sensor serving for the measuring process, which is slidably guided in the measuring tube, follows the movements of the piston under the influence of a magnetic force acting between the piston and the position sensor. A transmitter / receiver of the displacement measuring device, located on a housing cover, transmits a measuring radiation through the relevant open end of the measuring tube to the position sensor and receives the radiation reflected by it. Because the interior of the measuring tube thus forms a measuring zone independent of the physical state of the housing interior, a space with constant media pressure and constant media density is available for the passage of the measuring radiation, such as ultrasound.With a constant speed of sound, a displacement measurement can be carried out easily and accurately using a displacement measuring device with an ultrasonic transmitter / receiver, without the need for error correction. It goes without saying that a laser measurement can also be performed using the measuring tube.

[0011] According to the characterizing part of claim 1, it is further provided that the measuring tube is connected to the environment at the housing cover, which is opposite the housing cover containing the seat of the displacement measuring device. The pressure-resistant measuring tube is thus pressureless, so that no particularly complex sealing is required at the passage that forms the seat for the displacement measuring device. With the pressureless measuring tube, the displacement measuring device can also be removed from the piston accumulator after the completion of the measuring periods without interrupting its operation.

[0012] To generate the magnetic force forcing the subsequent movements of the position sensor in the measuring tube, a permanent magnet device can advantageously be provided on the piston, which drives the position sensor, which is made of a ferromagnetic material or is provided with ferromagnetic components, during the travel movements of the piston.

[0013] To generate a particularly high attractive force acting on the position sensor, a permanent magnet device can also be provided on the position sensor, for example a hard magnetic ferrite core located in the position sensor.

[0014] In a particularly advantageous manner, the permanent magnet device on the piston can have a magnetic ring fixed to the passage of the piston and surrounding the measuring tube.

[0015] In particularly advantageous embodiments, in which the position sensor comprises two circular disks extending in a radial plane relative to the longitudinal axis and connected by a coaxial, radially inwardly offset connecting part, the axial distance between the flat end surfaces of the disks preferably corresponds to the axial height of the magnetic ring on the piston. With the axial polarity of the magnetic ring, a high magnetic flux density and a strong magnetic force are generated across the disks of the position sensor, ensuring reliable follow-up movement of the position sensor.

[0016] As a permanent magnet device on the position sensor, a ferrite core can advantageously be provided in the connecting part of the discs, which is polarized in the axial direction opposite to the magnetic ring.

[0017] To magnetically decouple the magnetic ring from the piston material, in advantageous embodiments, the magnetic ring is connected to the piston via an intermediate body made of non-magnetic material. This intermediate body can be made of a thermosetting plastic and secured to the piston by screws, which are preferably also non-magnetic.

[0018] Advantageously, the arrangement can be such that the measuring tube is firmly connected at one end to a housing cover, for example by means of a soldered or welded connection, and engages with its other end in a passage located on the other housing cover, leading to the outside, in which the open end of the tube is sealed against the housing interior and a seat for the displacement measuring device is formed.

[0019] The seat of the respective housing cover can accommodate the transmitter / receiver for transmitting and receiving an optical or preferably ultrasonic-acoustic measuring radiation passing through the open end of the measuring tube.

[0020] The seat for the position measuring device can be provided on the housing cover adjacent to the oil-side working chamber. This advantageously allows the connection connections of the position measuring device and the pipe leading to the associated hydraulic system, which is connected to a connection opening located on this housing cover, to be located on the same side of the accumulator housing.

[0021] The invention is explained in detail below with reference to exemplary embodiments illustrated in the drawings. They show: Fig. 1 shows a shortened longitudinal section of an embodiment of the piston accumulator according to the invention; and Fig. 2 shows a longitudinal section, also shown in shortened form, of a second embodiment.

[0022] The piston accumulator shown in the drawing has an accumulator housing, designated as a whole by 1, which in both embodiments shown has as its main part a cylinder tube 3 forming a round hollow cylinder. This is tightly closed at both ends by a screwed-in housing cover 5 and 7, between which a piston 9 can be freely moved along the longitudinal axis 11 of the housing. The piston 9 separates a gas-side working chamber 13, which receives a working gas, such as nitrogen under a filling pressure, as a compressible medium, from a working chamber 15, which receives an incompressible medium, such as hydraulic oil. To connect this working chamber 15 to an associated hydraulic system (not shown), a connection opening 16 is provided in the housing cover 7 adjacent to the oil-side working chamber 15. This connection opening is arranged in the region between the longitudinal axis 11 and the radially outer end of the housing cover 7.On the opposite housing cover 5, which borders the gas-side working chamber 13, a filling channel 17 is provided, also offset from the longitudinal axis 11, at the outer end of which a filling valve 21 of a conventional type is arranged, through which a filling quantity of the working gas under filling pressure can be introduced into the working chamber 13. In a coaxial arrangement with the longitudinal axis 11, a through-opening 27 is also formed in this housing cover 5, which borders the gas-side working chamber 13. This through-opening has the form of a stepped bore with an inner, enlarged bore section 23, which forms a suitable seat for the inserted, open end 25 of a measuring tube 29, in which the open end 25 of the measuring tube 29 is sealed against the adjacent working chamber 13. With its opposite end 26, the measuring tube 29 engages in a coaxial through-bore 28 in the housing cover 7 adjacent to the oil-side working chamber 15.The bore 28 is stepped, similar to the through-opening 27 on the other housing cover 5, with the end 26 of the measuring tube 29 fittingly received in a bore section where sealing elements 19 and 20 seal the tube end 26 against the working chamber 15. The measuring tube 29, which is made of a pressure-resistant, non-magnetic metallic material, is secured to the housing cover 5 by means of a soldered or welded connection 24 at its end 25, which sits in the bore section 23 of the housing cover 5 adjacent to the gas-side working chamber 13. The measuring tube 29 extends inside the storage housing over its entire length.

[0023] A central passage 31 is formed in the piston 9 for the measuring tube 29. Otherwise, the piston 9 is designed in the manner usual for such accumulator pistons and has recessed annular grooves 33 and 35 on its outer circumference for piston seals (not shown), as well as, offset from these in the direction of the two axial end regions, shallower annular grooves 37 and 39 for guide strips (also not shown). As is also usual for such pistons, the piston 9 has a round, pot-shaped recess 41 on the piston side that faces the gas-side working chamber 13 in the accumulator housing 1, the flat bottom 43 of which is located approximately halfway along the axial length of the piston 9. The passage 31 has a through-bore 51 that extends, coaxially to the longitudinal axis 11, from the bottom 43 to the piston end face.In the bore area adjacent to the base 43, the bore has a circular cylindrical extension 53, which forms the seat for an annular body 45, which is secured in the extension 53 by screws 47 running parallel to the bore 51. Annular grooves 49 and 50 are formed in the non-expanded part of the bore 51 for sealing rings.

[0024] The annular body 45 secured in the extension 53 forms the support for a permanent magnet device that generates a magnetic force whose attractive force acting on a position sensor 57 displaceable in the measuring tube 29 forces the position sensor 57 to follow the displacement movements of the piston 9 in the measuring tube 29. In the illustrated embodiments, the permanent magnet device of the piston 9 is formed by a magnetic ring 55, which is fixed by adhesive to the free surface of the annular body 45 aligned with the base 43. For the magnetic decoupling of the magnetic ring 55 from the metallic piston 9, the screws 47 and the annular body 45 are made of thermosetting plastic.

[0025] In the embodiment of Fig. 1 The position sensor 57 is made of a ferromagnetic material as a one-piece round body, which has a flat circular disk 58 at each of its two axially opposite ends, on the outer diameter of which disk the position sensor 57 is displaceably guided in the measuring tube 29. The disks 58 are integrally connected to one another via a connecting part 59 with a reduced diameter. The axial spacing of the disks 58 is adapted to the axial height of the magnetic ring 55 such that the end faces of the disks 58 are aligned with the axial end faces of the magnetic ring 55, so that an optimal magnetic flux is formed with the magnetic ring 55. The end face of the disk 58 of the position sensor 57, which faces the end 26 of the measuring tube 29, forms the reflection surface for the measuring radiation entering the measuring tube 29 from the end 26.

[0026] The stepped bore 28 of the housing cover 7, which receives the end 26 of the measuring tube 29, has, in the same way as the bore 51 on the passage 31 of the piston 9, a circular-cylindrical extension 54 in which the same annular body 45, as used as a plastic body on the passage 31 of the piston 9, is received and secured by screws 47. The annular body 45 forms a suitable enclosure for the inserted end section of the measuring tube 29 on the housing cover 7. The displacement measuring device has a transmitter / receiver 65 for an ultrasonic measuring method, for which the outer, enlarged bore section 67 of the bore 28 in the oil-side housing cover 7 forms a seat.Starting from this bore section 67, an ultrasonic transducer with a disc-shaped piezoceramic 68 extends into the end region of the tube 29 in order to determine the distance to the reflection surface on the facing disc 58 of the position sensor 57.

[0027] The embodiment of Fig. 2 differs from Fig.1 only insofar as, instead of the connecting part 59, which is integral with the discs 58 of the position sensor 57, a hard magnetic ferrite rod 71 is inserted as a connecting part between the discs 58. This rod is oriented such that its polarity is opposite to the axial polarity of the magnetic ring 55, resulting in a strong magnetic force and thus ensuring particularly reliable tracking of the position sensor 57 during the travel movements of the piston 9.

[0028] It is understood that instead of the ultrasonic measuring method, other types of measuring radiation can be used, for example, using optical methods with laser light or monochromatic visible light. With a measuring zone enclosed in the measuring tube 29 and isolated from the housing interior, the measuring process can be carried out from any selected end 25 or 26 of the measuring tube 29. Therefore, unlike shown, the transmitter / receiver 65 could also be arranged on the gas-side housing cover 5, with the enlarged, end-side bore section 73 of the through-opening 27 forming the seat for the displacement measuring device.

Claims

1. Hydropneumatic piston accumulator comprising an accumulator housing (1) having a cylinder tube (3) which defines a longitudinal axis (11) and which is closed at both ends by a respective housing lid (5, 7) and in which a piston (9) is longitudinally movable, the piston separating, within the housing, a work chamber (13) for a compressible medium such as a working gas, from a work chamber for an incompressible medium such as hydraulic oil, and comprising a displacement measuring device that contactlessly determines the position of the piston (9) in the housing, the displacement measuring device having a non-magnetic measurement tube (29) that extends along the longitudinal axis (11) from one housing lid (5) to the other housing lid (7) through a bushing (31) formed in the piston (9) and is sealed from the internal chamber of the housing (1), characterised in that a position encoder (57) is displaceably guided in the tube (29) and tracks the piston movements in the measurement tube (29) by way of a magnetic force acting between itself and the piston (9), in that a transceiver (65) of the displacement measuring device is arranged on one of the housing lids (5, 7), which transceiver transmits to the position encoder (57) measurement radiation passing through the relevant open end (25, 26) of the measurement tube (29) and receives radiation reflected by said position encoder, and in that the measurement tube (29) is connected to the surroundings at the housing lid (5) that is opposite the housing lid (7) having the seat (67) for the displacement measuring device.

2. Piston accumulator according to claim 1, characterised in that a permanent magnet device (55) is provided on the piston (9) for generating the magnetic force that forces the tracking movements by the position encoder (57) in the measurement tube (29).

3. Piston accumulator according to claim 1, characterised in that a permanent magnet device (71) is also provided on the position encoder (57) for forcing the magnetic force that forces the tracking movements by the position encoder (57) in the measurement tube (29).

4. Piston accumulator according to claim 3, characterised in that the permanent magnet device (55) on the piston (9) has a magnetic ring (55) that is secured to the bushing (31) of the piston (9) and surrounds the measurement tube (29).

5. Piston accumulator according to claim 4, characterised in that the position encoder (57) has two circular discs (58) that extend in a radial plane with respect to the longitudinal axis (11) and are interconnected by a coaxial, radially inwardly offset connection part (59; 71) in such a way that the axial distance between the planar end faces of the discs (58) corresponds to the axial height of the magnetic ring (55) on the piston (9).

6. Piston accumulator according to claim 4 or claim 5, characterised in that the magnetic ring (55) is connected to the piston (9) by means of an intermediate member (45) consisting of a non-magnetic material.

7. Piston accumulator according to any of the preceding claims, characterised in that the measurement tube (29) is rigidly connected to the housing lid (5) at one end (25), and its other end (26) engages in an outwardly leading passage (28) that is located on the other housing lid (7) and in which the open end (26) of the tube (29) is sealed from the housing internal chamber and a seat (67) for the displacement measuring device is formed.

8. Piston accumulator according to claim 7, characterised in that the seat (67) of the relevant housing lid (7) accommodates the transceiver (65) for emitting and receiving optical or preferably acoustic measurement radiation passing through the open end (26) of the measurement tube (29).

9. Piston accumulator according to claim 7 or claim 8, characterised in that the seat (67) for the displacement measuring device is provided on the housing lid (7) that adjoins the oil-side work chamber (15).