Abstract:
The invention relates to a dry-running piston rod sealing arrangement ( 1 ) for sealing a piston rod ( 2 ) mounted in a longitudinally displaceable manner. The sealing arrangement comprises at least one sealing ring ( 5 ) having a sealing surface ( 5   a ), an actuator ( 7 ), a sensor ( 8 ), and a chamber ring ( 3 ) containing the sealing ring ( 5 ). The actuator ( 7 ) comprises an active connection in relation to the sealing ring ( 5 ), such that the sealing surface ( 5   a ) can be radially displaced in relation to the piston rod ( 2 ). The actuator ( 7 ) can be controlled according to a measuring value detected by the sensor ( 8 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/EP2005/055494, filed Oct. 24, 2005, which claims the benefit of EP Patent Application No. 04405656.2 filed Oct. 22, 2004, the disclosures of both of which applications are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a dry-running piston rod sealing arrangement. The invention further relates to a method for the sealing of a piston rod having a dry-running piston rod sealing arrangement. 
     A dry-running piston rod sealing arrangement for a dry-running piston compressor having a longitudinally movable piston rod is known from the document EP 0933566 A1. This dry-running sealing arrangement includes sealing elements of a dry-running material such as carbon, graphite or plastic. The sealing element has a sealing surface which contacts the piston rod and forms a rubbing contact seal with respect to the piston rod in this way. This friction has the consequence of increasing wear of the sealing element; the sealing action of the sealing element is gradually reduced after a maximum permissible wear has been exceeded and the sealing element then has to be replaced relatively quickly. The friction of the sealing element on the piston rod moreover generates frictional heat which is difficult to dissipate, which has the consequence that the maximum pressure difference which can be sealed or the mean piston speed has to be restricted. The known piston rod sealing systems used for the oil-free sealing of gases, also termed a packing or dry-running sealing arrangement, are subjected to a high mechanical and thermal loading which has the disadvantageous consequence that the service life of the sealing elements, the maximum pressure difference which can be sealed and also the mean piston speed are restricted. 
     SUMMARY OF THE INVENTION 
     It is thus an object of the present invention to propose a more advantageous dry-running sealing arrangement and also an advantageous method for the sealing of a piston rod with a dry-running seal. 
     This object is satisfied with a dry-running sealing arrangement having the features of the embodiment disclosed herein. Further embodiments relate to further advantageously designed dry-running sealing arrangements. The object is further satisfied with a method having the features of the embodiment disclosed herein. Further embodiments relate to further advantageous method steps. 
     The object is in particular satisfied with a dry-running piston rod sealing arrangement for the sealing of a longitudinal movably supported piston rod comprising at least one sealing ring having a sealing surface, an actuator, a sensor and also a chamber ring within which the sealing ring is arranged, with the actuator having an operative connection with respect to the sealing ring such that the sealing surface can be radially displaced relative to the piston rod, and wherein the actuator can be controlled in dependence on a measured value detected by the sensor. 
     The dry-running sealing arrangement in accordance with the invention has the advantage that the position of the sealing element or its sealing surface with respect to the surface of the piston rod can be controlled with the help of an actuator and is thus variable so that, on the one hand, it is preferably avoided that the sealing surface contacts the piston rod and, on the other hand, the gap width between the sealing surface and the piston rod can be subjected to follow-up regulation, preferably such that the gap width is kept as small as possible. 
     In the method in accordance with the invention for the sealing of the longitudinal movably supported piston rod the position of the sealing elements is thus controllably changed in dependence on a measurable value of the dry-running piston rod sealing arrangement, also termed the control value. By way of example, one of the distance between the sealing surface and the piston rod surface, the temperature of the piston rod, the quantity of leakage gas, the contact pressure force of the sealing element on the piston rod or the pressure difference between two sealing elements is suitable as the control value. This control value is detected with the aid of a sensor. This control value is also directed to a regulating device. The regulating device controls the actuator and thus the position of the sealing element, i.e. the position of the sealing surface until the control value corresponds to a preset desired value. The position of the sealing surfaces is preferably controlled in such a way that the pressure drop across a sealing ring lies within a predetermined range of values or at a predetermined value. The position of the sealing surfaces can for example also be controlled in such a way that essentially the same pressure drop is present across each controllable sealing ring. 
     The position of the sealing element is preferably regulated in such a way that a contact-free gap seal with a small gap width of fractions of millimeters is maintained between the sealing surface and the piston rod, for example a gap width in the range between 0 and 0.3 mm. The sealing elements could also be controlled in such a way that a gap width of zero results in that the sealing surface of the sealing element contacts the piston rod without or with only a negligible small contact pressing force. Since the sealing element does not contact the piston rod, or hardly touches the piston rod, it has no wear or only an extremely low wear so that the sealing elements rarely have to be replaced and the dry-running sealing arrangement can preferably be operated in service-free manner for a longer period of time. The dry-running sealing arrangement in accordance with the invention has the advantage that the pressure difference can preferably be controlled across each sealing element. In this way a situation can in particular be avoided in which an excessively high pressure difference with correspondingly high wear is present across one or more sealing elements. It has been shown that for non-controllable sealing elements a specific sealing element frequently wears excessively and thereby become unfit for operation, whereby a further sealing element is exposed to excessive wear, so that through this resulting chain reaction the entire dry-running sealing arrangement becomes unusable relatively soon. The arrangement in accordance with the invention prevents such an uncontrolled chain reaction for sealing elements arranged following one another along the piston rod. 
     The dry-running sealing arrangement in accordance with the invention has the further advantage that the sealing surface of the sealing element does not or hardly touches the surface of the moving piston rod so that thereby no frictional heat or only a small frictional heat arises. 
     The dry-running sealing arrangement in accordance with the invention thus has a higher service-life for lower leakage and is in particular also suitable for high pressure differences and/or high average piston rod speeds or piston speeds. The dry-running sealing arrangement in accordance with the invention thus permits a dry-running compressor with a high pumping performance to be built. Moreover, the dry-running sealing arrangement in accordance with the invention is also suitable for the sealing of gases with a low molecular weight, such as for example hydrogen. 
     The invention will be described in the following with the aid of Figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a piston rod seal of a dry-running piston compressor; 
         FIG. 2  is a partial view of a longitudinal section of a dry-running sealing arrangement; 
         FIG. 2   a  is a front view of a segmented sealing ring from the direction C; 
         FIG. 2   b  is a front view of a passive cover ring seen from the direction C; 
         FIG. 2   c  is a partial view of a longitudinal section of a further embodiment of a dry-running sealing arrangement; 
         FIG. 2   d  is a front view of a support ring seen from the direction C; 
         FIG. 2   e  is a front view of a further embodiment of a segmented sealing ring seen from the direction C; 
         FIG. 3  is a partial view of a further longitudinal section of a dry-running sealing arrangement; 
         FIG. 3   a  is a front view of a segmented sealing ring seen from the direction D; 
         FIG. 4   a  is a front view of a further segmented sealing ring; 
         FIG. 4   b  is a front view of a further segmented sealing ring; 
         FIG. 5   a  is a front view of a further segmented sealing ring; 
         FIG. 5   b  is a detailed view of the point of overlap of the sealing ring in accordance with  FIG. 5   a;    
         FIG. 5   c  is the sealing ring in accordance with  FIG. 5   a  with an elastic cover ring; 
         FIG. 5   d  is the sealing ring in accordance with  FIG. 5   c  from the direction C; 
         FIG. 6  is a partial view of a further longitudinal section of a dry-running sealing arrangement; 
         FIG. 7  is a view of a one-piece sealing ring; and 
         FIG. 7   a  is a detailed view of the point of overlap of the sealing ring in accordance with  FIG. 7 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a dry-running piston rod sealing arrangement  1  of a dry-running piston compressor having a piston rod  2  which is longitudinally movably supported in the direction of movement K, with the cylinder being located in the installed state at the side A and the piston rod drive at the side B. The dry-running sealing arrangement  1  is designed as a piston rod seal  1  having a packing, with the packing including a plurality of chamber rings  3  arranged in sequence with sealing rings  5  arranged therein. The dry-running sealing arrangement  1  includes a restrictor ring  4  and also a plurality of sealing rings  5 . In an advantageous design, as is shown by the top three chamber rings  3 , a cover ring  14 , a sealing ring  5  and also a support ring  17  are arranged alongside one another in the direction of extent of the piston rod  2 . Within the chamber ring  3  only a single sealing ring  5  can however also be provided, as shown in one chamber ring  3 . The piston rod  2  moves to and fro in the direction K. The piston rod seal  1  moreover includes a leakage gas extraction  6 . 
       FIG. 2  shows in a longitudinal section two chamber rings  3  and also a sealing ring  5  of the dry-running sealing arrangement  1  of the invention. The entire dry-running sealing arrangement  1  includes, as shown in  FIG. 1 , preferably a plurality of chamber rings  3  with sealing rings  5  arranged one behind the other in the direction of extent of the piston rod  2 . The chamber ring  3  shown in  FIG. 2  has a projecting, ring-like, chamber ring part  3   a  to which a piezoelectric actuator  7  is secured. The chamber ring  3  includes moreover two support surfaces  3   b ,  3   c  extending perpendicular to the longitudinal direction of the piston rod  2 . 
     The sealing ring  5  is shown in  FIG. 2   a  in a view from the direction C. The sealing ring  5  consists of three identically designed sealing ring segments  5   b ,  5   c ,  5   d  which are slightly spaced apart at the gap  5   g . The gap  5   g  has for example a width in the range from 0.1 to 0.5 mm. 
     In  FIG. 2   a  the actuator  7  which is associated with the sealing ring segment  5   b  is shown in broken lines. The actuator  7  is located, seen from the direction C, behind the sealing ring segment  5   b . In analogy to this an actuator  7  is also associated with the sealing ring segments  5   c ,  5   d , but is not however shown. Each sealing ring segment  5   b ,  5   c ,  5   d  thus has its own actuator  7  with the gap  5   g  being made so wide that the sealing ring segments  5   b ,  5   c ,  5   d  can be displaced in the radial direction R at least with respect to the piston rod  2 . 
       FIG. 2  shows a section of the sealing ring segment  5   b  along the line A-A. The sealing ring  5 , i.e. its sealing ring segments  5   b ,  5   c ,  5   d , has a sealing surface  5   a  oriented towards the piston rod  2 . The sealing ring shown in  FIG. 2  is surrounded by spring  9  so that the sealing ring segments  5   b ,  5   c ,  5   d  are held together while forming the whole sealing ring  5 . Three actuators  7  which are uniformly spaced apart in the peripheral direction are secured to the chamber ring part  3   a , with each sealing ring segment  5   b ,  5   c ,  5   d  being connected to a respective actuator  7 , so that each sealing ring segment  5   b ,  5   c ,  5   d  is displaceably supported in the radial direction R and can be controlled by one actuator each. 
     In the illustrated embodiment a sensor  8  is arranged inside at least one of the sealing ring segments  5   b  which detects the distance to the surface of the piston rod  2 . The sensor  8  and also the actuator  7  are connected via electrical leads  10   a  to a regulating device  10 . In the illustrated embodiment the regulating device  10  determines, with the aid of a sensor  8 , the spacing between the surface of the piston rod  2  and preferably the sealing surface  5   a , with the regulating device  10  controlling the actuator  7  and the sealing ring segment  5   b ,  5   c ,  5   d  connected to it in such a way that the gap width S adopts a desired value preset for the regulating device  10 . Each sealing ring segment  5   b ,  5   c ,  5   d  is preferably connected to a separate actuator  7  so that the regulating device  10  controls three actuators  7  per sealing ring  5 . 
     The section of the sealing ring segment  5   b  shown in  FIG. 2  also shows that each sealing ring segment  5   b ,  5   c ,  5   d  preferably has an end face  5   k  which preferably projects as shown in the longitudinal direction of the piston rod  2  and has a profile matched relative to the support surface  3   b . In the illustrated embodiment the end face  5   k  and also the contact surface  3   b  extend perpendicular to the longitudinal direction of the piston rod  2 . The contact surface  3   b  and also the end face  5   k  could also extend in inclined manner with respect to the longitudinal direction of the piston rod  2 . During the compression movement of the piston rod, for example of the non-illustrated piston, a higher pressure arises at the side designated by A. The contact surface  3   b  and the end face  5   k  have the advantages that all sealing ring segments  5   b ,  5   c ,  5   d  contact the contact surface  3   b  at least with the end face  5   k  and are thus laterally supported and that the gap  5   g  extending in a radial direction is covered over to a large part by the contact surface  3   b  which reduces the leakage in the direction of extent of the piston rod  2 . The lateral support is in particular important in order to hold the sealing ring  5  in a defined position since, during the operation of the piston compressor, an oscillating dynamic pressure profile arises within the piston rod sealing arrangement with considerable pressure fluctuations which act on the sealing ring  5 . 
     The sealing ring  5  can be arranged and designed such that a gap  18  results between the sealing ring  5  and the chamber ring  3 , which permits a return flow of the fluid in the direction A during a suction phase of the piston compressor. 
     In an advantageous embodiment the pressure applied via a sealing ring  5  during the compression phase lies in the range between 50 and 75 bar. If two chamber rings  3  with the sealing rings  5  arranged therein are arranged after one another in the direction of extent of the longitudinal axis of the piston rod  2 , the maximum pressure of this exemplary piston rod sealing arrangement  1  amounts to between 100 and 150 bar; i.e. the total maximum pressure when using four chamber rings  3  each having a sealing ring  5  lies between 200 and 300 bar. 
       FIG. 2   b  shows a passive cover ring, that is to say, a non-actively actuatable cover ring  14 . As shown in  FIG. 1  the cover ring  14  is arranged alongside the sealing ring  5 . In the example of  FIG. 2  the cover ring  14  is arranged to the right, alongside the sealing ring  5 , with the inner space of the chamber ring  3  then having to be made correspondingly large. The cover ring  14  covers the radial gaps  5   g  and thus prevents a gas escape in the direction of extent K of the piston rod  2 . In order to avoid wear of this passive sealing ring  14  its internal diameter is made sufficiently large that no contact with the piston rod  2  results. The cover ring  14  can have a return flow groove  14   a  in a preferred design, with the cover ring  14  being arranged such that the return flow groove  14   a  is aligned towards the side A. 
       FIG. 2   c  shows in a longitudinal section a further embodiment of a dry-running sealing arrangement which, in distinction to the embodiment of  FIG. 2 , includes a cover ring  14  and a support ring  17 . The support ring  17  serves as a support for the sealing ring  5  in the direction of the longitudinal axis of the piston rod  2 , with the support ring  17  having apertures  17   a  as shown in the plan view of  FIG. 2   d  through which the projecting chamber ring parts  3   a  extend. 
     The support ring  17  could also be designed in such a way that it only includes a circular disc designated by  17   b  in  FIG. 2   c , the peripheral surface of which partly contacts the projecting chamber ring part  3   a.    
     The sealing ring  5  could also, as shown in the plan view in  FIG. 2   e , consist only of two sealing ring segments  5   b ,  5   c  which are each displaceably supported in the radial direction R via one actuator  7  each. 
       FIG. 3  shows in a partial view a further longitudinal section through an embodiment of the chamber ring  3  with sealing ring  5 , with the sensor  8  and also the regulating device  10  not being shown. A ring-like holder  12  is arranged in the inner space of the chamber ring  3  to which the piezoelectric actuator  7  and also a spring  11  are connected. The sealing ring  5  is now designed such that this contacts both the actuator  7  and also the spring  11 . The actuator  7  is in turn actuatable in such a way that the sealing ring  5  and thus the sealing surface  5   a  is displaceably mounted in the radial direction R to the piston rod  2 . The embodiment of the sealing ring  5  shown in  FIG. 3  has a sealing layer  5   e  with labyrinth grooves facing towards the piston rod  2  so that a sealing surface  5   a  having labyrinth grooves results. The actuator  7  is preferably controlled in such a way that a small gap continually exists between the surface of the piston rod  2  and the sealing surface  5   a  so that a gap seal results, with the labyrinth grooves additionally increasing the sealing action. The entire sealing ring  5  could consist of the same material. The sealing ring  5  can also consist, as shown in  FIG. 3 , of a base ring  5   f  and also a sealing layer  5   e  with the sealing layer consisting of a different material with respect to that of the base ring  5   f . The base ring  5   f  could for example consist of a metal and the sealing layer  5   e  of a material capable of dry-running such as plastic or ceramic. 
       FIG. 3   a  shows a front view of the sealing ring  5  shown in  FIG. 3  from the direction D. The sealing ring  5  is designed as a segmented sealing ring with radial gaps  5   g  and includes three sealing ring segments  5   b ,  5   c ,  5   d .  FIG. 3  shows a section through the sealing ring in accordance with  FIG. 3   a  along the line B-B. The actuator  7  is schematically illustrated for the sealing ring segment  5   b . Each sealing ring segment  5   b ,  5   c ,  5   d  preferably has an actuator  7  arranged in this way. In a further embodiment two actuators  7   a ,  7   b  could be associated with each sealing ring segment as shown for the sealing ring segment  5   d , with the two actuators jointly acting on the sealing ring segment  5   d  so that it is displaceable in the direction R. 
     Differently designed sealing rings  5  can be used in combination with the dry-running sealing arrangement  1  in accordance with the invention.  FIGS. 4   a ,  4   b  and  5   a  each show a front view of differently designed sealing rings  5 , with the point of action for the actuators  7  being located, as also shown in  FIG. 2   a , at the rear side of the sealing ring segments  5   b ,  5   c ,  5   d  and thus not being directly visible in the illustrated view. 
     The sealing ring  5  in accordance with  FIG. 4   a  has cuts  5   h  along which the sealing ring segments  5   b ,  5   c ,  5   d  are displaceably mounted in order to move them in the direction R. 
     The sealing ring in accordance with  FIG. 4   b  has tangentially extending cuts  5   h  with respect to the piston rod  2 . The sealing ring segments  5   b ,  5   c ,  5   d  are preferably displaceable parallel to the course of the cuts  5   h  in the direction R. The two sealing rings  5  shown in  FIGS. 4   a  and  4   b  are preferably used in combination with a cover ring  14 . 
     The sealing ring  5  in accordance with  FIG. 5   a  consists of three sealing ring segments  5   b ,  5   c ,  5   d , which, as shown in  FIG. 5   b , each have a point of abutment S 1  overlapping in the peripheral direction. Each sealing ring segment  5   b ,  5   c ,  5   d  is connected, for example as shown in  FIG. 2  or  FIG. 3 , via an actuator  7  to the respective chamber ring  3  and is displaceable in the radial direction R. It can prove advantageous to provide the sealing ring  5 , as shown in  FIG. 5   c , with a peripherally extending elastic sealing ring  15  which seals off the points of abutment in the radial direction. For this arrangement no additional adjacently disposed cover ring  14  is required as is shown in  FIG. 1  with the individual sealing ring  4  arranged in the chamber ring  3 . The sealing ring  15  can, as shown, be surrounded by an elastic spring  16 . The sealing ring  5  can, as shown in  FIGS. 5   c  and  5   d , have return flow grooves  5   i  extending in the radial direction, with the sealing ring  5  being arranged such that the return flow grooves  5   i  point to the side A shown in  FIG. 2 . 
       FIG. 6  shows, in a partial view, a further longitudinal section through an embodiment of a chamber ring  3  with the sealing ring  5  and a sensor  8  arranged in the chamber ring  3  which detects the pressure within the chamber ring  3 . An actuator  7  designed as an electro-magnet with a coil is arranged in the chamber ring  3 . Similar to the way shown in  FIG. 2   a  the sealing ring  5  is designed as a segmented ring consisting of three sealing ring segments  5   b ,  5   c ,  5   d . Each sealing ring segment  5   b ,  5   c ,  5   d  is connected to a metallic magnetizable holder  13 . Through an actuation of the actuator  7  each sealing ring segment can be individually displaced in the radial direction R so that the gap width S can be adjusted.  FIG. 6  shows at the left a further sensor  8  which is arranged in the left-hand chamber ring  3 , which is merely indicated. Both sensors  8  and also the actuators  7  are connected via the leads  10   a ,  10   b  to the regulating device  10 . In the illustrated embodiment the pressure in the chamber rings  3  is detected with the aid of the sensors  8  as a control value, and a position of the sealing ring segments  5   b ,  5   c ,  5   d  is preferably controlled in such a way that a preset desired pressure difference sets in neighboring chamber rings  3  or so that a preset desired pressure difference is not exceeded. 
       FIG. 7  shows a one-piece sealing ring  5  with overlapping joints  5   i ,  5   k .  FIG. 7   a  shows these joints  5   i ,  5   k  and also the gap S 1  in a side view from the viewing direction F. The sealing ring  5  is surrounded by a ring-like or tube-like actuator  7  whose peripheral length can be controllably extended or shortened, for example piezoelectrically, so that the sealing surface  5   a  of the sealing ring  5  in turn experiences a shift in the radial direction R relative to the piston rod  2  so that the gap width S can also be controlled and changed. The electrical leads  10   b  serve for the control of the piezoelectric actuator  7 . 
     All the sealing rings  5  of the dry-running sealing arrangement  1  preferably each have at least one actuator  7 . If the sealing ring  5  consists of sealing ring segments  5   b ,  5   c ,  5   d  then each sealing ring  5  preferably has its own actuator  7  for each sealing ring segment  5   b ,  5   c ,  5   d . The regulating device  10  preferably controls all actuators  7  of the dry-running sealing arrangement  1 , with the regulating device  10  detecting the values of a plurality of sensors  8  arranged in the dry-running sealing arrangement  1 . 
     The actuators  7  could also be designed, in addition to the illustrated embodiments operating with electrical energy, in such a way that these can be operated by flow energy, for example pneumatically or hydraulically, in order to generate a stroke movement. The adjustment path, i.e. the displacement path in the radial direction R which can be brought about by an actuator  7 , preferably lies in the range from a few tenths of a millimeter up to about one millimeter. 
     A plurality of sensors are suitable as the sensors  8 . For the measuring of the spacing between the piston rod  2  and the sealing ring segment  5   b ,  5   c ,  5   d  an inductive pick-up transducer is for example suitable. 
     The piston rod temperature serves as an indicator of the friction heat which is produced by the sealing system. In a possible regulating method the spacing between the sealing ring  6  and the piston rod  2  is slightly increased with a rise of the piston rod temperature until the temperature falls again. The measurement of the piston rod temperature can for example take place through a contact measurement by means of a sliding shoe, but preferably however in contact-free manner, for example with an infrared sensor or with a sensor arranged on the piston rod  2  the values of which can be transferred in contact-free manner. It can also prove advantageous to measure the mass flow at the leakage gas extraction  6 , for example with a thermal mass flow transducer. The actuators  7  could for example be controlled in such a way that a minimum quantity of gas at the leakage gas extraction is not fallen short of. 
     In contrast to the passive cover ring  14  shown in  FIG. 2   b , the cover ring  14  could also be designed as an actively controllable cover ring  14 , for example in the same way as the sealing ring  5  shown in  FIG. 3   a . Thus, a sealing ring  5  and a controllable cover ring  14  could be jointly arranged lying alongside one another in a chamber ring  3  in that, for example, the arrangements illustrated in  FIGS. 2 and 3  are jointly arranged within a chamber ring  3  for the control of one sealing ring  5  in each case, with the sealing ring  5  shown in  FIG. 3  executing the function of a cover ring  14  in that it is arranged such that the joints  5   g  of the sealing ring  5  are covered over so that the sealing ring and the cover ring  5 ,  14  lie alongside one another and can be individually controlled via the respective actuator  7 . 
     In an advantageous operating method the sealing ring  5  can be controlled in a first operating phase in such a way that the sealing surfaces  5   a  contact the piston rod  2  so that the sealing surfaces  5   a  wear against the piston rod  2  and thereby adopt the shape of the piston rod  2 . In a second operating phase the sealing ring  5  could be controlled in such a way that a predefined gap exists between the sealing surfaces  5   a  and the piston rod  2 . Since the run of the sealing surfaces  5   a  is matched to the run of the piston rod  2  in the second operating phase, the predefined gap can be kept very small so that a small leakage results in the longitudinal axis of the piston rod  2 .