Patent Publication Number: US-11378107-B2

Title: Piston and cylinder unit including a radially installed piston position detection unit

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to co-pending German Patent Application No. DE 10 2019 122 121.8 filed Aug. 16, 2019. 
     FIELD OF THE INVENTION 
     The invention relates to a piston and cylinder unit including a cylinder, a piston being supported in the cylinder to be axially movable and a piston position detection unit detecting the axial position of the piston in the cylinder. 
     Such piston and cylinder units are especially used in working machines, construction machines, agricultural machines, maritime machines and mechanical engineering. The units are especially hydraulic piston and 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 it is thus determined. 
     BACKGROUND OF THE INVENTION 
     A piston and cylinder unit is known from German utility model DE20 2014 001 604 U1. The piston and cylinder unit includes a cylinder, a piston being supported in the cylinder to be axially movable and a piston position detection unit detecting the axial position of the piston in the cylinder by high frequency technology. The piston position detection unit is arranged in a mounting bore in the cylinder extending in a radial direction. 
     A piston and cylinder unit is known from German patent DE 10 2016 120 665 B3. The piston and cylinder unit includes a cylinder, a piston being supported in the cylinder to be axially movable and a piston position detection unit detecting the axial position of the piston in the cylinder by high frequency technology. The piston position detection unit is arranged in a mounting bore in the cylinder extending in a radial direction. 
     A piston and cylinder unit is known from international patent application WO 03/069269 A2 corresponding to U.S. Pat. No. 7,095,944 B2. The piston and cylinder unit includes a cylinder, a piston being supported in the cylinder to be axially movable and a piston position detection unit detecting the axial position of the piston in the cylinder by high frequency technology. 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 and cylinder unit. 
     A piston and cylinder unit is known from US patent application US 2013/0312601 A1. The piston and cylinder unit includes a cylinder, a piston being supported in the cylinder to be axially movable and a piston position detection unit detecting the axial position of the piston in the cylinder by high frequency technology. The piston position detection unit is arranged in a mounting bore in the cylinder extending in a radial direction. 
     In the prior art of hydraulic piston and 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. 
     A position detection device including a microwave antenna arrangement is known from European patent application EP 1 752 792 A1 corresponding to U.S. Pat. No. 7,492,165 B2. 
     A waveguide-coupling device and a positioning sensor device for a hydraulic cylinder are known from German patent application DE 10 2016 106 747 A1 corresponding to US patent application US 2019/0207285 A1. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a piston and cylinder unit including a cylinder, a piston and a piston position detection unit. The cylinder has an interior and includes a mounting bore extending in a radial direction. The piston is supported in the cylinder to be movable in an axial direction. The piston position detection unit is designed and arranged to detect an axial position of the piston in the cylinder by high frequency technology. The piston position detection unit includes a housing and an electronic unit being arranged in the housing. The piston position detection unit is arranged in the mounting bore such that the interior of the cylinder is sealed from the surroundings of the piston and cylinder unit by the housing. 
     The present invention also relates to a piston position detection unit for detecting the position of a piston in a cylinder of a piston and cylinder unit. The piston position detection unit includes a housing having a longitudinal center axis. The piston position detection unit includes a housing having a longitudinal center axis. The piston position detection unit furthermore includes an electronic unit being arranged in the housing and including an antenna for sending and receiving high frequency signals through the housing. The sense of direction of main radiation of the antenna extends perpendicularly to the longitudinal axis of the housing. The piston position detection unit is designed to be arranged in a mounting bore in the cylinder such that the interior of the cylinder is sealed from the surroundings of the piston and cylinder unit by the housing. 
     The present invention also relates to a method of retrofitting a piston and cylinder unit with a piston position detection unit for detecting the position of a piston in a cylinder of the piston and cylinder unit. A mounting bore is created in the cylinder in a way that the mounting bore extends radially in the cylinder. A sensor signal bore is created in the cylinder in a way that the sensor signal bore extends axially in the cylinder and connects the mounting bore with the interior of the cylinder. The piston position detection unit is inserted into the mounting bore such that the interior of the cylinder is sealed from the surroundings of the piston and cylinder unit by the housing. 
     With the new piston position detection unit, it is possible to retrofit usual piston and cylinder units in a simple way for detecting the axial position of the piston in the cylinder. 
     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 30 MHz. 
     The main components of the piston and cylinder units are 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 and cylinder unit especially is a hydraulic piston and cylinder unit. However, it may also be a pneumatic piston and cylinder unit. 
     The new piston position detection unit uses a different arrangement principal than it is known from piston position detection units known from the prior art. 
     The detection, determination, evaluation, adjustment and provision of the position of the piston in the cylinder of a piston and cylinder unit is of interest in the technical field of working machines for different reasons. For example, it may be desired to 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 pistons after one another and a programmable order are also possible. Furthermore, allowable working regions within which the piston and cylinder unit may move, can be defined and reliably complied with. It is also possible to prevent an overload of the piston and cylinder unit by observing the position of the piston and the load. The load acting upon 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 and cylinder unit especially serves to steer, support, extend, pivot, lift or for other movements of the working machine or of a tool or a different part of the working machine. 
     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 unit is inserted into and removed from the housing, respectively, in the mounted position of the housing. In this way, replacement of the piston position detection unit is possible without having to disassemble the piston and cylinder unit. Replacement of the electronic unit may then be realized at the cylinder being completely filled with oil. Thus, emptying, filling and venting of the cylinder are not necessary. 
     The mounting bore extending radially in the cylinder can be easily created in the cylinder, especially by drilling. This starts 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 low space requirement in the axial direction of the piston and cylinder unit. In this way, it can be considered without problems in a new construction of a piston and cylinder unit and added to existing piston and cylinder units. Consequently, an integration of the new piston position detection unit does not require a geometrical change of the piston and cylinder unit compared to a piston and 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. In this case, the mounting bore is arranged in the cylinder head of the piston and 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 for the necessary sending and receiving of the high frequency sensor signals used for the detection of the position. In case the piston and cylinder unit is a hydraulic piston and cylinder unit, this sensor signal bore is filled with hydraulic oil. 
     The mounting bore may be connected to the surroundings 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 not to arrange such a compensation bore and to 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 unit being arranged in the housing. The electronic unit may be sealed against the interior of the cylinder by the housing. In this way, the intrusion of hydraulic oil into the interior of the piston position detection unit is prevented by the housing. The core element of the piston position detection unit—namely the electronic unit—is located in this interior. The electronic unit at least fulfills the function of sending 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 a plastic material or a ceramic material. 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 and 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 out 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 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 may include a first channel and a second channel at its outer circumference, a seal being arranged in each of the channels. 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 between the first channel and the second channel as seen in the radial direction. 
     The effective sealing surfaces of the seals may be substantially equally great. In this way, an arrangement of the piston position detection unit in the mounting bore being neutral concerning forces is attained. This results in the piston position detection unit not having to be secured at all or only having to be secured by simple securing means in the mounting bore. The piston position detection unit may be fixed by a simple securing element, for example a securing ring. However, it is also possible to fix the piston position detection unit by a screw connection in the mounting bore, for example. 
     The piston position detection unit may include a connection element for transmitting data from the electronic unit, the connection element being connected to the electronic unit and to the housing. The connection element may be a cabled or wireless connection element. In case of a cabled 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 by W-Fi, Bluetooth or a different suitable wireless transmission standard is also possible. 
     The piston and cylinder unit, with the exception of 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 and cylinder unit is not changed compared to a piston and cylinder unit not including such a piston position detection unit. 
     Consequently, there is no need for geometrical adaptation of the working machine. 
     The electronic unit may include an antenna for sending and receiving high frequency signals through the housing. The antenna may be arranged on the electronic unit and the electronic unit 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 for undisturbed sending and receiving of high frequency signals. 
     The housing may include a first aligning element and the electronic unit may include a corresponding second aligning element, wherein the first aligning element and the second aligning element are coordinated in a way that the electronic unit is fully mountable in the housing only in exactly one orientation. In this way, incorrect assembly of the electronic unit in the housing is prevented. 
     The first aligning element may be designed as a groove being arranged eccentrically in an axial end region of the housing and the second aligning element may be designed as a tongue being arranged equally eccentrically in a corresponding axial end portion of the electronic unit. The aligning elements commonly form a tongue and groove connection. The tongue can thus be arranged in the groove only in exactly one relative arrangement with respect to the groove. A third aligning element may be arranged at the housing and a corresponding fourth aligning element may be arranged at the mounting bore and at the cylinder, respectively. The third aligning element may be a protrusion, for example, and the fourth aligning element may be a recess or vice versa. Other geometrical designs are also possible. In this way, it is ensured that the housing can be arranged in the cylinder of the piston and cylinder unit only in exactly one orientation. 
     Due to the aligning 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 and 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. 
     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 radar signals. The high frequency signals may be especially frequency modulated continuous wave radar signals. It is possible to send different frequencies in a certain order. 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 sends a sending signal the frequency of which 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 “continuous-wave radar” at WIKIPEDIA (https://en.wikipedia.org/wiki/Continuous-wave_radar). 
     Advantageous developments of the invention result from the claims, the description and the drawings. 
     The advantages of features and of combinations of a plurality of features mentioned at the beginning of the description only serve as examples and may be used alternatively or cumulatively without the necessity of embodiments according to the invention having to obtain these advantages. 
     The following applies with respect to the disclosure—not the scope of protection—of the original application and the patent: Further features may be taken from the drawings, in particular from the illustrated designs and the dimensions of a plurality of components with respect to one another as well as from their relative arrangement and their operative connection. The combination of features of different embodiments of the invention or of features of different claims independent of the chosen references of the claims is also possible, and it is motivated herewith. This also relates to features which are illustrated in separate drawings, or which are mentioned when describing them. These features may also be combined with features of different claims. Furthermore, it is possible that further embodiments of the invention do not have the features mentioned in the claims which, however, does not apply to the independent claims of the granted patent. 
     The number of the features mentioned in the claims and in the description is to be understood to cover this exact number and a greater number than the mentioned number without having to explicitly use the adverb “at least”. For example, if a mounting bore is mentioned, this is to be understood such that there is exactly one mounting bore or there are two mounting bores or more mounting bores. Additional features may be added to these features, or these features may be the only features of the respective product. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. In the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  illustrates a sectional view of an exemplary embodiment of a new piston and cylinder unit including a new piston position detection unit. 
         FIG. 2  illustrates an enlarged view of a part of the piston and cylinder unit according to  FIG. 1 . 
         FIG. 3  illustrates the detail A of the piston and cylinder unit of  FIG. 2 . 
         FIG. 4  illustrates a view of a part of the piston and cylinder unit according to  FIG. 1  from above. 
         FIG. 5  illustrates a perspective exploded view of a part of the piston and cylinder unit according to  FIG. 1 . 
         FIG. 6  illustrates a perspective view of an exemplary embodiment of an electronic unit of the piston position detection unit of the piston and cylinder unit according to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring now in greater detail to the drawings,  FIG. 1-6  illustrate different views of an exemplary embodiment of a new piston and cylinder unit  1  as well as its parts. 
     In  FIG. 1 , the discontinuation lines indicate that the piston and 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 and 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 and cylinder unit  1  at a working machine (not illustrated) is arranged. 
     In the present example, since it is a hydraulic piston and cylinder unit  1 , the interior  3  is filled with oil  53 . For this purpose, the cylinder  2  includes an oil connection  6  and an oil connection  24 . Oil lines (not illustrated) are connected to the oil connections  6 ,  24 . A hydraulic pump (not illustrated) subjects the piston  7  by the oil  53  with pressure in a way as it is known taken in isolation such that the piston  7  and the piston rod  8  being connected therewith move in the respective sense of direction along the longitudinal center axis  54  of the piston and cylinder unit  1 . In this way, oil enters through the oil connections  6 ,  24  into the interior  3  of the cylinder  2  and exits from the interior  3 , respectively, depending on the sense of direction of the movement of the piston  7  within the cylinder  2 .  FIGS. 1 and 2  illustrate the position of the piston  7  all the way to the right—i.e. the retracted position of the piston and cylinder unit  1 . 
     As it has been described above, the piston and cylinder unit  1  includes the piston  7 . The piston  7  is connected to the piston rod  8 , a piston rod eye  9  being arranged at one of its axial ends. The piston rod eye  9  also includes a bearing bushing  10 . The bearing bushing  10  serves for the operative connection of the piston  9  with a tool (not illustrated) or a different part of the working machine. 
     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 fixedly arranged on the piston rod  8  such that they cannot be rotated with respect to one another and it is secured by 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  is commonly supported with the piston rod  8  and the piston rod eye  9  to be movable back and forth within the cylinder tube  55  of the cylinder  2 . 
     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 . 
     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 (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  are to be best seen in the enlarged illustration according to  FIG. 3  and the exploded view according to  FIG. 5 . The structure of the electronic unit  30  is illustrated in  FIG. 6  in greater detail. For reasons of clarity of the drawings, the components of the piston position detection unit  28  have not been designated with reference numerals in  FIGS. 1 and 2 . 
     The piston position detection unit  28  includes a housing  29  and an electronic unit  30  being arranged in the housing  29 . 
     The housing  29  is designed to be cylindrical and it is closed by a bottom  31  at its lower end (see  FIG. 5 ). The opposite upper end is open such that the electronic unit  30  can be inserted there. The housing  29  is made of a material being permeable for high frequency signals. The material especially is a thermoplastic plastic material. 
     The housing  29  includes a first aligning element  32  in the region of its closed bottom  31 , the first aligning element  32  being designed as a groove  33  and being arranged eccentrically in the cylindrical housing  29 . A second aligning element  34  of the electronic unit  30  engages the first aligning element  32 . The second aligning element  34  is designed as a tongue  35 . In this way, a tongue and groove connection is formed. The second aligning element  34  is also arranged eccentrically at the electronic unit  30 . In this example, the tongue  35  is formed by a board  36  of the electronic unit  30 . Thus, the entire 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 a third aligning element  49 . In this example, the third aligning element  49  is designed as a protrusion  50  being located at the housing  29 . The mounting bore  27  includes a corresponding fourth aligning 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 . 
     At its opposite axial end, the board  36  is connected to a connection element  37  for transmitting data from the electronic unit  30 . The connection element  37  in its mounted position is connected to the electronic unit  30  as well as to 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 channel  40 , a second channel  41  and a third channel  42  at its outer circumference. A first seal  43  is arranged in the first channel  40 , a second seal  44  is arranged in the second channel  41  and a third seal  45  is arranged in the third channel  42 . The first seal  43  being located in the first channel  40  serves to seal against the surroundings. 
     The seals  44 ,  45  form a pair of seals and serve to seal the interior  3  of the cylinder  2  being filled with oil  53 . The sensor signal bore  26  in which oil  53  is located is arranged between the first channel  40  and the second channel  41  in a radial direction—i.e. in the direction of the longitudinal center axis  47 . The effective sealing surfaces of the seals  44 ,  45  are approximately equally great such that an arrangement of the piston position detection unit  28  in the mounting bore  27  being neutral concerning forces is attained. 
     A number of electronic components is arranged on the board  36 . One of these components is an antenna  46  being designed to send and receive high frequency signals through the housing  29 . The other components serve to determine, calculate, evaluate and transmit data in the piston position detection unit  28 . Taken in isolation, they are known to the skilled person and thus not further described. 
     The antenna  46  is arranged on the board  36 , the 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 sense of direction of main radiation of the antenna  46  thus extends perpendicularly to the longitudinal center axis  47  of the housing  29 . Thus, the sense of direction of main radiation 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 signal bore  26  onto the piston  7  and that the signals reflected by the piston  7  can be received by the antenna  46 . 
     During 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 contact the piston  7 , they are reflected by the piston  7  and they return along the same path and are received by the antenna  46 . The electronic unit  30  with its additional electronic components and the software executed by these components carries out an evaluation and thus determines the current position of the piston  7  along the longitudinal center axis  54 . This determination can be conducted permanently, in defined time intervals or at specific points in time. By the connecting element  37 , the result or a command being associated with the result is transmitted to an electronic computing unit of the working machine connected therewith—a part of which is the piston and cylinder unit  1 . 
     Many variations and modifications may be made to the preferred embodiments of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of the present invention, as defined by the following claims.