EP 3783230 1 PISTON-CYLINDER UNIT INCLUDING A RADIALLY INSTALLED PISTON POSITION DETECTION UNIT TECHNICAL FIELD OF THE INVENTION The invention relates to a piston-cylinder unit comprising a cylinder, a piston axially movably supported in the cylinder, and a piston position detection unit which detects the axial position of the piston in the cylinder.
Such piston-cylinder units are especially used in working machines, construction machines, agricultural machines, maritime machines and mechanical engineering.
The units are especially hydraulic piston-cylinder units.
The position of the piston in the cylinder often serves to attain a defined position of a tool being indirectly connected to the piston and is therefore determined.
BACKGROUND ART A piston-cylinder unit including a cylinder, a piston mounted axially movably in the cylinder and a piston position detection unit detecting the axial position of the piston in the cylinder by high frequency technology is known from the German utility model DE 20 2014 001 604 U1. The piston position detection unit is arranged in a mounting bore in the cylinder extending in a radial direction.
A piston-cylinder unit including a cylinder, a piston being supported axially movably in the cylinder and a piston position detection unit detecting the axial position of the piston in the cylinder by high frequency technology is known from the US patent application US2013/0312601 A1. The piston position detection unit is arranged in a mounting bore in the cylinder extending in a radial direction.
A piston-cylinder unit including a cylinder, a piston being supported axially movably in the cylinder and a piston position detection unit detecting the axial position of the piston in the cylinder by high frequency technology is known from the international patent application WO 03/069269 A2. The piston position detecting unit includes a coupling probe, a retaining system and a waveguide being arranged in a plurality of axial bores in the cylinder head of the cylinder of the piston-cylinder unit.
EP 3783230 2 In the prior art of hydraulic piston-cylinder units of working machines, piston position detection units determining the axial position of the piston in the cylinder by magnetostrictive sensors are generally known.
The structure of such magnetostrictive sensors is comparatively technically complex and expensive.
Adistance measuring device including a microwave antenna arrangement is known from the European patent application EP 1 752 792 A1. A waveguide coupling device and a positioning sensor device for a hydraulic cylinder are known from the German patent application DE 10 2016 106 747 A1. PROBLEM OF THE INVENTION The invention is based on the problem of providing a piston position detection unit with which conventional piston-cylinder units can be retrofitted in a simple manner for a detection of the axial position of the piston in the cylinder.
SOLUTION According to the invention, the problem of the invention is solved by the features of the independent patent claims.
Further preferred embodiments according to the invention are to be taken from the dependent patent claims.
DESCRIPTION OF THE INVENTION The invention relates to a piston-cylinder unit including a cylinder, a piston axially movably mounted in the cylinder, and a piston position detection unit which detects the axial position of the piston in the cylinder by means of high-frequency technology.
The piston position detection unit is arranged in a mounting bore extending radially in the cylinder.
The invention further relates to a piston position detection unit for detecting the position of a piston in a cylinder of a piston-cylinder unit.
The piston position detection unit includes a housing having a longitudinal center axis.
The piston position detection unit furthermore includes an electronic assembly being arranged in the housing and including an antenna for transmitting and receiving high frequency signals through the housing.
The sense of direction of main radiation of the antenna extends perpendicularly to the longitudinal central axis of the housing.
EP 3783230 3
The term of high frequency technology as used in this application is to be understood according to its broad interpretation, i.e., to cover all frequencies between approximately 3 MHz and approximately 30 THz.
Especially, it is not to be understood according to the narrow definition of the International
Telecommunications Union according to which the frequency range of high frequency technology only covers frequencies between 3 MHz and 30 MHz.
The piston-cylinder unit includes as the main components a piston and a cylinder.
The cylinder is to be understood as a greater unit which especially includes the sub-components of a cylinder tube and of a cylinder head.
A piston is to be understood in this application as the component which moves in the cylinder tube, and which forms a closed chamber with the cylinder tube.
The piston is especially connected to a piston rod.
The piston-cylinder unit especially is a hydraulic piston-cylinder unit.
However, it may also be a pneumatic piston-cylinder unit.
The new piston position detection unit uses a different arrangement principle than piston position detection units known from most of the prior art.
The detection, determination, evaluation, adjustment and provision of the position of the piston in the cylinder of a piston-cylinder unit is of interest in the technical field of working machines for different reasons.
For example, it may be desired to safely reach a defined end position of the piston and thus of the tool of the working machine being indirectly connected to the piston.
An automation in the sense of computer-controlled attaining of different positions of the piston one after another and a programmable sequence are also possible.
Furthermore, allowable working regions within which the piston-cylinder unit may move, can be defined and reliably complied with.
It is also possible to prevent an overload of the piston- cylinder unit by observing the position of the piston and the load.
The load acting on the piston and the cylinder can be determined by measuring pressure, temperature and position.
Appropriate measures can be proposed or initiated when there is an overload.
For example, the working machine may be a wheel loader, excavator, tipper, crane or stacker or a lifting platform.
The piston-cylinder unit especially serves to steering, supporting, extending, pivoting, lifting or otherwise moving the working machine or a tool or other part of the working machine.
EP 3783230
4 The piston position detection unit may be designed as a compact cartridge including the sensor as well as the evaluation electronics.
Consequently, during assembly and disassembly, respectively, the entire piston position detection unit is inserted and removed, respectively.
However, it is also possible that the housing of the piston position detection unit is fixedly mounted in the cylinder and that the electronic assembly is inserted into and removed from the housing, respectively, in the mounted position.
In this way, replacement of the piston position detection unit is possible without having to disassemble the piston-cylinder unit.
Replacement of the electronic assembly may then be realized at the cylinder being filled completely with oil.
Thus, emptying, filling, and venting of the cylinder are not necessary.
The mounting bore extending radially in the cylinder can be very easily created in the cylinder, especially by drilling.
This is done starting at the outer surface of the cylinder head.
The mounting bore may have a diameter being comparatively small compared to its length such that the mounting bore has a small space requirement in the axial direction of the piston-cylinder unit.
Thus, it can be easily incorporated in a new piston-cylinder unit design without additional material requirements and can be retrofitted in existing piston-cylinder units.
Consequently, an integration of the new
— piston position detection unit does not require a geometrical change of the piston- cylinder unit compared to a piston-cylinder unit not including such a piston position detection unit.
In addition, there is no substantial weakening of the structure of the cylinder.
The cylinder may include a cylinder head, wherein in this case the mounting bore is arranged in the cylinder head of the piston-cylinder unit.
The piston position detection unit may be arranged in the mounting bore such that its longest dimension extends radially in the cylinder head.
In this way, the existing installation space of the cylinder head for the arrangement of the piston position detection unit is effectively used.
The mounting bore may be operatively connected to the interior of the cylinder by an axially extending sensor signal bore.
This sensor signal bore allows the reguired transmission and reception of the high freguency sensor signals used for the detection of the position.
In case the piston-cylinder unit is a hydraulic piston- cylinder unit, this sensor signal bore is filled with hydraulic oil.
EP 3783230
The mounting bore may be connected to the surrounding by a compensation bore.
In this way, assembly of the piston position detection unit in the otherwise closed mounting bore being sealed by the piston position detection unit is simplified.
However, it is also possible to not provide such a compensation bore and to 5 accept a certain compression of the air in the mounting bore.
For example, the compensation bore may be arranged in the housing - especially in the bottom of the housing - of the piston position detection unit.
However, it is also possible that the compensation bore is located in the cylinder.
The compensation bore may be arranged in an axial end portion of the mounting bore facing away from the opening of the mounting bore.
The piston position detection unit includes a housing and an electronic assembly arranged in the housing.
The electronic assembly may be sealed against the interior of the cylinder by the housing.
In this way, the housing prevents hydraulic oil from intruding into the interior of the piston position detection unit, in which the core element of the piston position detection unit - namely the electronic assembly - is located.
The electronic assembly at least fulfills the function of transmitting and receiving the high frequency signals.
However, it can also fulfill all additional desired functions of the piston position detection unit resulting in a compact self- sufficient unit.
Consequently, the piston position detection unit may be designed as a so-called smart sensor.
This means that in addition to the actual sensor, means for determining, calculating, evaluating and transmitting the data are contained in the piston position detection unit.
The temperature may be part of this data.
The housing of the piston position detection unit may be especially made of plastic or ceramic.
The material and the structure of the housing are chosen such that they are suitable to be used in this region being subjected to high pressure.
It is possible that a pressure of approximately 600 bar or more prevails in this region of a piston-cylinder unit - depending on its dimensioning.
The material of the housing of the piston position detection unit is furthermore chosen such that it is permeable for high frequency signals.
For this reason, for example metal materials are not suitable.
The housing may be made of a thermoplastic plastic material, especially a polyaryletherketone, especially polyetheretherketone (PEEK). Such plastic materials have the above-described desired properties of high-pressure resistance and permeability for high frequency signals at the same time.
It has been found
EP 3783230 6 that a housing of PEEK can be used at a pressure of up to 800 bar or more without problem.
The housing of the piston position detection unit has a longitudinal center axis.
The housing of the piston position detection unit may be designed to be cylindrical.
This design allows for simple assembly of the piston position detection unit in the mounting bore.
Other shapes, as rectangular or oval, for example, are also possible.
The housing has a first groove and a second groove on its outer periphery, in each of which a seal is arranged.
These two seals serve to seal the interior of the cylinder against the surroundings in the region in which the mounting bore is located.
The connection of the mounting bore to the interior of the cylinder is realized by the sensor signal bore.
The sensor signal bore is arranged in the radial direction, i.e. in the direction of the longitudinal center axis of the housing, between the first groove and the second groove.
The effective sealing surfaces of the seals are substantially of equal size.
In this way, a force-neutral arrangement of the piston position detection unit in the mounting bore is achieved.
This results in that the piston position detection unit does not have to be secured in the mounting bore, or only with simple securing means.
The piston position detection unit can be secured with a simple securing element, e.g., a retaining ring.
However, it would also be possible, for example, to secure the piston position detection unit in the mounting bore by means of a screw connection.
The piston position detection unit may include a connection element for transmitting data from the electronic assembly, the connection element being connected to the electronic assembly and to the housing.
The connection element may be a wired or wireless connection element.
In case of a wired connection element, it is a plug or a socket.
A possible suitable example for this is a M12 plug and a M12 socket, respectively.
However, wireless transmission via WLAN, Bluetooth or another suitable wireless transmission standard is also possible.
The piston position detection unit, except for a part of the connection element, may be completely arranged in the mounting bore.
It may also be completely arranged in the mounting bore.
This means that the outer shape of the piston-cylinder unit is not changed compared to a piston-cylinder unit not including such a piston position
EP 3783230 7 detection unit.
Consequently, there is no need for geometrical adaptation of the working machine.
The electronic assembly may include an antenna for transmitting and receiving high frequency signals through the housing.
The antenna may be arranged on the electronic assembly and the electronic assembly may be arranged in the housing such that the high frequency signals are directed through the sensor signal bore.
In this way, the material of the housing and the free space provided by the sensor signal bore allow undisturbed transmission and reception of the high frequency signals.
The housing may include a first alignment element and the electronic assembly may include a corresponding second alignment element, wherein the first alignment element and the second alignment element are matching each other such that the electronic assembly is fully mountable in the housing in exactly one orientation only.
In this way, incorrect assembly of the electronic assembly in the housing is prevented.
The first alignment element may be designed as a groove being arranged eccentrically in an axial end region of the housing and the second alignment element may be designed as a tongue being arranged equally eccentrically in a corresponding axial end portion of the electronic assembly, which together form a
—tongue-and-groove connection.
The tongue can thus only be arranged in the groove in exactly one relative arrangement with respect to the groove.
A third alignment element may be arranged at the housing and a corresponding fourth alignment element may be arranged at the mounting bore and the cylinder, respectively.
The third alignment element may be a protrusion, for example, and the fourth alignment element may be a recess or vice versa.
Other geometrical designs are also possible.
In this way, it is ensured that the housing can only be arranged in the cylinder of the piston-cylinder unit in exactly one orientation.
Due to the alignment elements, it is overall achieved that the sense of direction of main radiation of the antenna is correctly aligned.
The sense of direction of main radiation of the antenna then extends perpendicularly to the longitudinal center axis of the housing of the piston position detection unit and along the longitudinal axis of the piston-cylinder unit or parallel thereto.
The sense of direction of main radiation of the antenna extends in the direction of the sensor signal bore and of the piston.
EP 3783230 8 The high frequency signals may be microwave signals.
The high frequency signals may have a frequency of at least 20 GHz, especially at least 50 GHz, especially at least 100 GHz, especially between 20 GHz and 400 GHz, especially between 100 GHz and 400 GHz, especially between 100 GHz and 300 GHz, especially between 100 GHz and 150 GHz, especially approximately 120 GHz.
The high frequency signals may be continuous wave signals.
The high frequency signals may be especially frequency modulated continuous wave signals.
It is possible to send different frequencies in a certain sequence.
For example, these — may be frequencies of 120 GHz, 121 GHz and 122 GHz and so forth.
A frequency modulated continuous wave radar (FMCW radar) continuously transmits a sending signal whose frequency changes.
In contrast to an unmodulated radar (CW radar), a frequency modulated continuous wave radar can change its operating frequency during the measurement.
Due to this change of the frequency, the time reference required for measuring the distance to the measured object (here: the piston) is provided.
The distance measurement is then realized by a frequency comparison of the received signals with the sent signals.
Since this measurement principle taken in isolation is known from the prior art, it is not further described and instead it is referred to the article "Dauerstrichradar" at WIKIPEDIA — (https://de.wikipedia.org/wiki/Dauerstrichradar). Advantageous further developments of the invention result from the claims, the description, and the drawings.
The advantages of features and of combinations of several features mentioned in the description are merely exemplary and can have an alternative or cumulative effect without the advantages necessarily having to be achieved by embodiments according to the invention.
The features mentioned in the patent claims and the description are to be understood with regard to their guantity in such a way that exactly this guantity or a quantity greater than the mentioned quantity is present without requiring an explicit use of the adverb "at least". If, for example, one mounting hole is mentioned, this is to be understood as meaning that exactly one mounting hole, two mounting holes or more mounting holes are present.
EP 3783230 9 The reference signs contained in the patent claims do not represent a limitation of the scope of the subject matter protected by the patent claims. They merely serve the purpose of making the patent claims easier to understand. BRIEF DESCRIPTION OF THE FIGURES Inthe following, the invention is further explained and described with reference to preferred embodiments shown in the figures.
Fig. 1 illustrates a sectional view of an exemplary embodiment of a new piston-cyl- inder unit including a new piston position detection unit.
Fig. 2 illustrates an enlarged view of a part of the piston-cylinder unit according to
Fig. 1.
Fig. 3 illustrates the detail A of the piston-cylinder unit of Fig. 2.
Fig. 4 illustrates a view of a part of the piston-cylinder unit according to Fig. 1 from above.
Fig. 5 illustrates a perspective exploded view of a part of the piston-cylinder unit according to Fig. 1.
Fig. 6 illustrates a perspective view of an exemplary embodiment of an electronic assembly of the piston position detection unit of the piston-cylinder unit according to Fig. 1. FIGURE DESCRIPTION — Fig. 1-6 illustrate different views of an exemplary embodiment of a new piston- cylinder unit 1 as well as its parts. In Fig. 1, the discontinuation lines indicate that the piston-cylinder unit 1 actually is designed to be longer and that only a part is illustrated. Similar discontinuation lines exist in Figs. 2, 4 and 5. In Fig. 3, the illustration ends without a discontinuation line where the dashed line in Fig. 2 (detail A) is arranged. The piston-cylinder unit 1 includes a cylinder 2 including a cylinder tube 55, an interior 3 and a cylinder head 4. In the region of the cylinder head 4, a bearing bushing 5 for the support of the piston-cylinder unit 1 at a working machine, which is not illustrated, is arranged.
EP 3783230 10 In the present example, it is a hydraulic piston-cylinder unit 1, so that the interior 3 is filled with oil 53. For this purpose, the cylinder 2 includes an oil connection 6 and an oil connection 24. Qil lines not illustrated are connected to the oil connections 6, 24. Also not shown is a hydraulic pump by means of which, in a manner known per se, the piston 7 is pressurized by means of the oil 53 in such a way that the piston 7 and the piston rod 8 connected thereto move in the respective sense of direction along the longitudinal center axis 54 of the piston-cylinder unit 1. In this way, oil enters or leaves the interior 3 of the cylinder 2 through the oil connections 6, 24, depending on the direction of movement of the piston 7 in the cylinder 2. Figs. 1 and 2 show the position of the piston 7 moved to the far right, i.e. the retracted position of the piston-cylinder unit 1. As it has been described above, the piston-cylinder unit 1 furthermore includes the piston 7. The piston 7 is connected to the piston rod 8, at one axial end of which a piston rod eye 9 is arranged. The piston rod eye 9 also includes a bearing bushing
10. The bearing bush 10 is used for indirect connection of the piston 7 to a tool or other part of the working machine, which is not shown. The piston rod 8 is supported by a guiding bushing 11 to be translationally movable in an axial direction along the longitudinal center axis 54. A rod seal 12, an O-ring 13 and a supporting ring 14 are provided for supporting and sealing. Another O-ring 15, a scraper 16 and a slide bearing 17 are arranged at the other axial end of the guiding bushing 11. The piston 7 is arranged non-rotatably on the piston rod 8 and secured by means of a locking nut 18. Furthermore, an O-ring 19, a piston guiding ring 20, a piston seal 21, another piston guiding ring 22 and a welding seam 23 are located at the — piston 7. In this way, the piston 7, together with the piston rod 8 and the piston rod eye 9, is supported within the cylinder tube 55 of the cylinder 2 in a translationally back and forth moving sealing manner. A chamber 25 in the cylinder head 4 is connected to the part of the interior 3 which is formed by the cylinder tube 55. The chamber 25 also forms a part of the interior 3 and is filled with oil 53. The chamber 25 is connected to the oil connection 24. An axially extending sensor signal bore 26 is connected to the chamber 25. The sensor signal bore 26 is also connected to the interior 3 and filled with oil 53.
EP 3783230
11 The sensor signal bore 26 is connected to a mounting bore 27 extending radially in the cylinder 2. The mounting bore 27 extends to the outer surface of the cylinder head 4 and may be connected to the surroundings by a compensation bore, which is not illustrated.
A piston position detection unit 28 is arranged in the mounting bore 27. The piston position detection unit 28 serves to detect the axial position of the piston 7 in the cylinder 2 by high frequency technology.
The details of the piston position detection unit 28 can best be seen in the enlarged illustration according to Fig. 3 and the exploded view according to Fig. 5. The structure of the electronic assembly 30 is illustrated in Fig. 6 in more detail.
For reasons of clarity, the components of the piston position detection unit 28 have not been designated with reference signs in Figs. 1 and 2.
The piston position detection unit 28 includes a housing 29 and an electronic assembly 30 being arranged in the housing 29.
The housing 29 is cylindrically formed and closed at its lower end (see Fig. 5) by a bottom 31. The opposite upper end is open so that the electronic assembly 30 can be inserted from there.
The housing 29 is made of a material that is permeable to high-frequency signals.
In particular, it is a thermoplastic material.
The housing 29 includes a first alignment element 32 in the region of its closed bottom 31, the first alignment element 32 being designed as a groove 33 and being arranged eccentrically in the cylindrical housing 29. A second alignment element 34 of the electronic assembly 30 engages the first alignment element 32. The second alignment element 34 is designed as a tongue 35. In this way, a tongue and groove connection is formed.
The second alignment element 34 is also formed eccentrically at the electronic assembly 30. In this example, the tongue 35 is formed by a circuit board 36 of the electronic assembly 30. Thus, the entire circuit board 36 is arranged eccentrically.
However, this could also be realized in a different way.
The correct alignment of the housing 29 in the mounting bore 27 is realized by means of a third alignment element 49, which is formed here as a protrusion 50 on the housing 29. The mounting bore 27 includes a corresponding fourth alignment element 51 being designed as a recess 52 in this case.
To improve perceptibility, this region is additionally illustrated at an enlarged scale in Fig. 4.
EP 3783230 12 At its opposite axial end, the circuit board 36 is connected to a connection element 37 for transmitting data from the electronic assembly 30. In its mounted position, the connection element 37 is connected to the electronic assembly 30 as well as the housing 29. The connection to the housing 29 is realized by a threaded connection 38, for example. In the present case, the connection element 37 is a M12 plug. However, it could also be a different connection element 37. The housing 30 and thus the piston position detection unit 28 are securely mounted in the mounting bore 27 by a securing ring 39. The housing 29 includes a first groove 40, a second groove 41 and a third groove 42 at its outer circumference. A first seal 43 is arranged in the first groove 40, a second seal 44 is arranged in the second groove 41 and a third seal 45 is arranged in the third groove 42. The first seal 43 being located in the first groove 40 serves to seal against the surroundings. The seals 44, 45, on the other hand, form a sealing pair and serve to seal the — interior 3 of the cylinder 2 filled with oil 53. The sensor signal bore 26, in which oil 53 is located, is arranged in the radial direction - i.e. in the direction of the longitudinal center axis 47 - between the first groove 40 and the second groove
41. The effective sealing surfaces of the seals 44, 45 are approximately the same size, so that a force-neutral arrangement of the piston position detection unit 28 in the mounting bore 27 results. A number of electronic components are arranged on the circuit board 36. These include an antenna 46 configured for transmitting and receiving high frequency signals through the housing 29. The other components serve for determination, calculation, evaluation and transmission of data in the piston position detection unit 28, are in themselves familiar to the person skilled in the art and will therefore not be explained further. The antenna 46 is arranged on the circuit board 36, the circuit board 36 is arranged in the housing 29 and the housing 29 is aligned in the cylinder head 4 such that the high frequency signals of the antenna 46 are directed through the sensor signal bore 26. The main radiation direction sense of the antenna 46 thus extends perpendicularly to the longitudinal center axis 47 of the housing 29. Thus, the main radiation direction sense of the antenna 46 extends along the longitudinal center axis 48 of the sensor signal bore 26 or offset thereto in a way that the high frequency signals are directed from the antenna 46 through the sensor signal bore
EP 3783230 13 26 onto the piston 7 and that the signals reflected by the piston 7 can be received by the antenna 46. In operation of the piston position detection unit 28, it sends high frequency signals by the antenna 46 through the housing 29, the sensor signal bore 26 and - depending on the position of the piston 7 - through a part of the interior 3. The signals reach the piston 7, are reflected by the piston 7 and return along the same path and are received by the antenna 46. The electronic assembly 30 performs an evaluation with its further electronic components and the program executed by them and thus determines the current
— position of the piston 7 along the longitudinal center axis 54. This determination can be performed permanently, at defined time intervals or at specific points in time.
Via the connection element 37, the result or a command associated therewith is passed on to an electronic computing unit of the working machine connected thereto, of which the piston-cylinder unit 1 is a part.
EP 3783230 14 LIST OF REFERENCE SIGNS 1 Piston-cylinder unit 2 Cylinder 3 Interior 4 Cylinder head 5 Bearing bushing 6 Oil connection 7 Piston 8 Piston rod 9 Piston rod eye 10 Bearing bushing 11 Guiding bushing 12 Rod seal 13 O-ring 14 Support ring 15 O-ring 16 Scraper 17 Slide bearing 18 Locking nut 19 O-ring 20 Piston guiding ring 21 Piston seal 22 Piston guiding ring 23 Welding seam 24 Oil connection 25 Chamber 26 Sensor signal bore 27 Mounting bore 28 Piston position detecting unit 29 Housing 30 Electronic assembly 31 Bottom 32 First alignment element 33 Groove 34 Second alignment element 35 Tongue
EP 3783230 15 36 Circuit board 37 Connection element 38 Threaded connection 39 Securing ring 40 First groove 41 Second groove 42 Third groove 43 First seal 44 Second seal 45 Third seal 46 Antenna 47 Longitudinal center axis 48 Longitudinal center axis 49 Third alignment element 50 Protrusion 51 Fourth alignment element 52 Recess 53 Oil 54 Longitudinal center axis for cylinder Cylinder tube 56 Air