Abstract:
The oil control ring ( 2 ) extends in a circumferential direction ( 2   x ) about a center ( 2   l ) and has a longitudinal axis ( 2   m ) that passes through the center ( 2   l ), wherein the oil control ring ( 2 ) has an end face ( 2   d ) that faces the center ( 2   l ), and wherein the oil control ring ( 2 ) has a first lateral surface ( 2   s ), a second lateral surface ( 2   t ), and an outer surface ( 2   u ) facing away from the center ( 2   l ), wherein the oil control ring ( 2 ) has a plurality of channels ( 2   c ) extending toward the center ( 2   l ) on the first lateral surface ( 2   s ), said channels being arranged at mutual distances in the circumferential direction ( 2   x ) and extending over the entire width of the first lateral surface ( 2   s ) in the radial direction and thereby forming a fluid-conducting connection between the end face ( 2   d ) and the outer surface ( 2   u ), and wherein crown parts ( 2   i ) extending in the circumferential direction ( 2   x ) are arranged between pairs of channels ( 2   c ), wherein each crown part ( 2   i ) protrudes beyond the respective channel ( 2   c ) in the direction of extent of the longitudinal axis ( 2   m ) and forms a lateral channel surface ( 2   w ) for the channel ( 2   c ), wherein at least one of the crown parts ( 5   i ) is designed as a long crown part ( 2   p ) and extends over an angular range (α) between 60 degrees and 350 degrees in the circumferential direction ( 2   x ). 212×2121.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Phase Application of PCT International Application No. PCT/EP2012/050993, International Filing Date Jan. 23, 2012, claiming priority of European Patent Application No. 11151750.4, filed Jan. 21, 2011, which is hereby incorporated by reference. 
     The invention relates to an oil scraper ring. 
     BACKGROUND OF THE INVENTION 
     The document EP 1 446 597 B1 discloses an oil scraper ring which can, in particular be used as an oil barrier for piston rods of ship diesel engines. The oil scraper ring has oil scraper lips composed of plastic oriented towards the piston rod side which oil scraper lips scrape the oil present at the piston rod and, for example, supply this again to a crank housing. This known oil scraper ring has the disadvantage that the scraping is not very efficient and/or that the oil can overcome the oil scraper ring. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to form an advantageous oil scraper ring which ensures a reliable oil scraping during a long period of operation. 
     The object is in particular satisfied by an oil scraper ring which extends in a circumferential direction about a center and which has a longitudinal axis extending through the center, wherein the oil scraper ring has an end face oriented towards the center, and wherein the oil scraper ring comprises a first side surface, a second side surface, as well as an outer surface facing away with respect to the center, wherein the oil scraper ring has a plurality of passages extending towards the center at the first side surface, which passages are mutually spaced apart in the circumferential direction and which extend in the radial direction over the complete width of the first side surface and thereby form a fluid conducting connection between the end face and the outer surface, and wherein a respective crown part extending in the circumferential direction is arranged between two passages, wherein the crown part respectively projects over the passage in the direction of extent of the longitudinal axis and in this connection forms a passage side surface for the passage, wherein at least one of the crown parts is configured as a long crown part and extends over an angular range a between 60 degrees and 350 degrees in the circumferential direction. 
     The long crown part is preferably configured such that the long crown part has no outlet in the radial direction. 
     The oil scraper ring in accordance with the invention is preferably used in connection with an oil scraper ring package, preferably for sealing a horizontally running piston rod. At least two oil scraper rings are arranged lying next to one another in the oil scraper ring package, wherein the long crown parts are arranged above the piston rod, advantageously, such that all oil scraper rings are identically positioned with respect to the piston rod, wherein the oil scraper rings mutually touch one another. The long crown parts arranged above the piston rod have the effect that oil scraped from the piston rod by the oil scraper rings cannot escape upwardly from the oil scraper ring package, and, thus can only escape following the gravitational force downwardly and possibly laterally. This embodiment has the advantage that the oil can generally be scraped better from the piston rod and/or has the advantage that less oil can overcome the oil scraper ring package. 
     The invention is further satisfied, in particular by an oil scraper ring comprising a holding ring, as well as comprising a scraper having a scraper lip, wherein the scraper is arranged in the holding ring, such that the scraper lip is oriented towards the center of the oil scraper ring, in order to scrape oil at a piston rod, wherein the scraper is composed of a plurality of scraper segments arranged following one another in the circumferential direction of the oil scraper ring, and wherein the holding ring has a groove for the form-fitted reception of the scraper segments, and wherein the holding ring has an abutment position, and wherein the holding ring has at least one first end face made of plastic oriented towards the center of the oil scraper ring, and wherein the scraper is composed of a material having a larger hardness than the plastic forming the first end face, wherein the scraper lip of the scraper has a contact position oriented towards the center and wherein the scraper and the holding ring are configured mutually adapted such that both the at least first end face and also the contact position can lie at the piston rod. 
     The oil scraper ring in accordance with the invention has the advantage that this enables a substantial and efficient scraping of the oil present at the piston rod and that the oil scraper ring only has a small wear. In an advantageous embodiment the oil scraper ring in accordance with the invention comprises a scraper which has a larger hardness than the material of the holding ring which forms the first end face and which is determined for abutment at the piston rod. Such a scraper has a stable and, preferably also sharp, scraping edge which ensures an efficient scraping of the oil. Moreover, the oil scraper ring in accordance with the invention comprises a holding ring which has a first end face formed of plastic which is oriented towards the piston rod and which is determined for the contact at the piston rod. The oil scraper ring in accordance with the invention is configured in an advantageous embodiment such that both the first end face and also the scraping edge can simultaneously lie at the piston rod which has the consequence that the scraping edge only contacts at the piston rod with very little pressure or even no pressure, since a part of the, in particularly radially inwardly acting, forces are transferred via the first end face. The scraping edge thereby experiences a very small wear. Moreover, the position and orientation of the scraping edge is stabilized with respect to the piston rod, by the end face of the holding ring lying at the piston rod, and, in particular is stabilized also with respect to any arising movement. In a particularly advantageous embodiment the material forming the first end face is composed of a plastic with very good dry running properties, such as a filled PTFE or a high temperature poly-mer modified with filling materials suitable for dry running, such as PTFE, MoS2, graphite etc. The scraper or the complete oil scraper ring, with or without scraper, is preferably composed of a metal, such as grey cast, bronze and aluminum or of a plastic, in particular of a high temperature polymer such as PEEK, polyimide or PPS. 
     The scraper is composed of a plurality of scraper segments. The holding ring can be of one piece design or can be formed from a plurality of holding ring segments. The holding ring as well as the scraper ring are preferably designed and mutually adapted such that the lips of the scraper rings at least partly abut the holding ring, such that the lip is protected from an excessive load, since a force engaging at the scraper ring or respectively at the lip is directly transferred to the holding ring. 
     The oil scraper ring in accordance with the invention is, in particular particularly suitable for dry running compressors, since for a dry running compressor the contamination of the gas to be compressed by means of lubricant should safely be avoided. Moreover, already small oil leaks which penetrate into a dry running piston rod sealing system bring about its fast destruction. The reliable function of the oil scraper system is particularly important on the compression of oxygen. In this example, oil leaks can even lead to a fire. However, also when no acute danger from oil leaks is present, this at least leads to increased costs of operation, as well as to an environmental load, since the lubricant lost on the crank operation has to be continuously replaced and the leaking oil must be discarded. 
     The oil scraper ring in accordance with the invention is preferably used in an oil scraper ring package comprising a plurality of oil scraper rings arranged behind one another in the direction of extent of a piston rod. 
     The invention will be described in the following with reference to embodiments in detail. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings used for explaining the embodiments show: 
         FIG. 1  a perspective view of a first embodiment of an oil scraper ring; 
         FIG. 2  a top view of the oil scraper ring in accordance with  FIG. 1 ; 
         FIG. 3  a section through a horizontally arranged package comprising a plurality of oil scraper rings arranged following one another, wherein two are illustrated; 
         FIG. 4  a top view of a further embodiment of an oil scraper ring; 
         FIG. 5  a section through a horizontally arranged package comprising three oil scraper rings illustrated following one another as in  FIG. 4 ; 
         FIG. 6  a top view of a further embodiment of an oil scraper ring; 
         FIG. 7  a perspective view of a further embodiment of an oil scraper ring; 
         FIG. 8  a cross-section through the oil scraper ring illustrated in  FIG. 7 ; 
         FIG. 9  a cross-section through a further embodiment of an oil scraper ring; 
         FIG. 10  a cross-section through the oil scraper ring along the sectional line C-C; 
         FIG. 11  a view from below of the oil scraper ring in accordance with  FIG. 9 ; 
         FIG. 12  a cross-section through a holding ring segment along the sectional line D-D; 
         FIG. 13  a top view onto the holding ring segment; 
         FIG. 14  a cross-section through a scraper along the sectional line C-C; 
         FIG. 15  a perspective view of a scraper; 
         FIG. 16  a horizontally arranged package comprising three oil scraper rings arranged behind one another; 
         FIG. 17  a front view of an oil scraper ring illustrated in  FIG. 16  from direction B; 
         FIG. 18  a cross-section through a further embodiment of an oil scraper ring; and 
         FIG. 19  a top view onto a further oil scraper ring of one piece design. 
     
    
    
     Generally like parts are referred to using the same reference numerals in the drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  in a perspective view and  FIG. 2  in a top view show an oil scraper ring  2  which extends in a circumferential direction  2   x  about a center  2   l  and which has a longitudinal axis  2   m  extending through the center  2   l , wherein the oil scraper ring  2  has an end face  2   d  orientated towards the center  2   l , and wherein the oil scraper ring  2  has a first side surface  2   s , a second side surface  2   t , as well as an outer surface  2   u  facing away with respect to the center  2   l . The oil scraper ring  2  has a plurality of passages  2   c  extending towards the center  2   l  at the first side surface  2   s  which passages are mutually spaced apart in the circumferential direction  2   x  and which passages extend in the radial direction over the complete width of the first side surface  2   s  and thereby form a fluid conducting connection between the end face  2   d  and the outer surfaces  2   u . A crown part  2   i  is arranged extending in the circumferential direction between two passages  2   c , wherein the crown part  2   i  respectively projects over the passage  2   c  in the direction of extent of the longitudinal axis  2   m  and in this connection forms a passage side surface  2   w  for the passage  2   c . At least one of the crown parts  2   i  is configured as a long crown part  2   p  and extends in the direction of extent  2   x  over an angular range a between 60 degrees and 350 degrees. The oil scraper ring  2  moreover has a gap  2   g , which in the illustrated embodiment is arranged in a passage  2   c . The oil scraper arrangement  1  comprises an oil scraper ring  2 , as well as a clamping element  4  surrounding an oil scraper ring  2  along the outer surface  2   u  and lying in a recess  2   k.    
       FIG. 3  shows a horizontally extending oil scraper ring package, wherein two oil scraper rings  2  arranged following one another in the direction extent of a piston rod  6  are illustrated. The long crown parts  2   p  are arranged above and lying next to one another in the direction of extent to the piston rod  6 . The long crown parts  2   p  thereby form a barrier to the top in order to prevent that oil scraped at the end face  2   d  from the piston rod  6  can directly arrive in the upper inner space  7   a  of the housing  7 . Advantageously a security against rotation  5 , such as a pin, is further provided in order to prevent a rotation of the oil scraper rings  2  with respect to one another. Advantageously all long crown parts  2   p  are arranged with respect to the piston rod  6  in an identical position. 
       FIG. 5  shows a horizontally extending oil scraper ring package comprising three oil scraper rings  2  arranged following one another in the direction of extent to the piston rod  6 .  FIG. 4  shows a front view from the direction B of an oil scraper ring  2  arranged in  FIG. 5 . As illustrated in  FIG. 4  a recessed end face  2   e  is arranged set back with respect to the end face  2   d  in the radial direction, such that an intermediate  2   q  is formed between the long crown part  2   p  and the surface  6   a  of the piston rod  6 , and such that a scraper lip  2   n  is formed between the first end face  2   d  and the intermediate  2   q . The first end face  2   d , as illustrated in  FIG. 5  at least partly contacts at the surface  6   a  of the piston rod  6 , such that oil is scraped which, as illustrated with the fluid flow  8 , escapes to the outside via the passages  2   c . The passages  2   c  are arranged at the bottom in the circumferential direction  2   x  preferably at least along an angular range of 60 degrees, wherein a respective crown part  2   i  is arranged between two passages  2   c . Advantageously, each passage  2   c  has a width corresponding to an angular range of at least 10 degrees in the circumferential direction  2   x , such that each of the passages  2   c  extend over an angular range of at least 10 degrees in the direction of extent  2   x . A substantially semicircular long crown part  2   p  is arranged at the top between the left and right arranged passage  2   c  in the illustrated embodiment, which crown part  2   p  extends over an angular range of at least 60 degrees in dependence on the embodiment. The long crown part  2   p  is configured continuously in the circumferential direction such that the crown part  2   p  has no outlet. This embodiment has the advantage that the scraped oil, as illustrated by the fluid flow  8 , can only escape downwardly, since the oil scraper ring  2  does not have a continuous passage  2   c  towards the top in the radial direction. In a particularly advantageous embodiment, oil scraper rings  2  arranged next to one another, as illustrated in  FIG. 5 , have a security against rotation, for example, a fixing pin  5 , in order to prevent a rotation of the oil scraper rings  2  with respect to one another and, in order to preferably also prevent a rotation of the oil scraper ring  2  with respect to the housing  7 . 
       FIG. 6  shows a further embodiment of an oil scraper ring  2  in a top view having a long crown part  2   p  and having a plurality of passages  2   c  and crown parts  2   i  arranged in the circumferential direction  2   x . The long crown parts  2   p  extends over an angle α of more than 180 degrees, wherein the radial gap  2   g  extends in the long crown part  2   p . The oil scraper ring  2  is advantageously arranged in an oil scraper ring package such that the position referred to with  2   v  is arranged at the top, such that the crown part  2   p , starting from the position  2   v , extends over an angular range of at least 30 degrees in both directions of circumference. 
     The oil scraper rings  2  illustrated in  FIGS. 1 to 5  are preferably made of a plastic. 
       FIG. 7  in a perspective view and  FIG. 8  in a section show a further embodiment of an oil scraper ring  2  which is surrounded by a clamping element  4 . This oil scraper ring  2  is manufactured of metal, preferably of brass. 
     The oil scraper ring  2  in turn has a long crown part  2   p  and in the circumferential direction  2   x  has a plurality of passages  2   c  and crown parts  2   i . The abutment position  2   g  is configured running inclined in the illustrated embodiment, wherein a part of the clamping element  4  is still visible behind the abutment position  2   g.    
       FIG. 9  shows a further embodiment of an oil scraper ring  2  in a section. The oil scraper ring  2  is composed of at least a first ring part  2   y  and a second ring part  2   z , wherein the first and the second ring part  2   y ,  2   z  are connected to one another, preferably fixedly connected to one another, wherein the second ring part  2   z  is arranged between a center  2   l  and the first ring part  2   y , and wherein the second ring part  2   z  is preferably corn-posed of a plastic, and wherein the second ring part  2   z  forms the end face  2   d . The first ring part  2   y  can be formed of a plastic or also of a metal. The recessed end face  2   e  is arranged set back with respect to the first end face  2   d , such that only the first end face  2   d  contacts at the surface  6   a  of the piston rod  6 . 
       FIG. 10  shows an oil scraper ring  2  having a clamping element  4  along the sectional line C-C illustrated in  FIG. 11 .  FIG. 11  shows the same oil scraper arrangement  1  in a view from below. As is clear from  FIG. 11 , the oil scraper ring  2  is composed of three holding ring segments  2   a  arranged following one another in the circumferential direction  2   x , with a respective radially running abutment position  2   g  being present between the holding ring segments  2   a . The oil scraper ring  2  can also only be composed of two holding ring segments  2   a  or also of more than three holding ring segments  2   a . The oil scraper ring  2  has crown parts  2   i  arranged spaced apart in the circumferential direction  2   x  between which crown parts a passage  2   c  respectively extending in a radial direction with respect to the center  2   l  of the oil scraper ring  2  is arranged. A scraper  3  is arranged in the oil scraper ring  2  which scraper, in the illustrated embodiment, is composed of three scraper ring segments  3   e  arranged behind one another in the circumferential direction, wherein a respectively radially extending abutment part  3   b  is present between the scraper ring segments  3   e . The scraper  3  can also only be composed of two scraper segments  3   e  or also of more than three scraper segments  3   e . In the assembled state the oil scraper ring  2 , moreover, as illustrated in  FIG. 1 , comprises a clamping element  4  such as a spring, which encloses the oil scraper ring  2  from the outside, and brings about a bias acting against the center  2   l  onto the oil scraper ring  2  or the scraper  3  respectively. 
       FIG. 10  shows the oil scraper ring  2  and/or a holding ring segment  2   a  which has a surrounding groove  2   b  in which the scraper  3  respectively the scraper ring segment  3   e  is arranged. The scraper  3  has a scraper lip  3   a  which has a contact position  3   c  at its tip. The scraper  3  is preferably corn-posed of a metal, such as grey cast, bronze, brass and aluminum or of a high temperature polymer, such as PEEK, polyimide or PPS. The scraper  3  is composed of a material having a larger hardness than the plastic of the oil scraper ring  2  forming the first end face  2   d ,  2   f . The scraper  3  is arranged in the oil scraper ring  2  such that the scraper lip  3   a , as well as the contact position  3   c  are oriented towards the center  2   l  of the oil scraper ring  2  in order to scrape oil from a surface  6   a  of a piston rod  6 , only hinted at in the illustration. The groove  2   b  of the oil scraper ring  2  is advantageously configured adapted with respect to the scraper segment  3   a  such that the groove  2   b  permits a form-fitted reception of the scraper segment  3   a . The oil scraper ring  2  comprises at least one end face  2   d ,  2   f  of plastic oriented towards the center  2   l  of the scraper ring  1 . The scraper  3  and the oil scraper ring  2  are configured mutually adapted such that both the at least first end face  2   d  and also the contact position  3   c  can simultaneously contact the piston rod  6 . In an advantageous embodiment the oil scraper ring  2  comprises a first and a second end face  2   d ,  2   f  which both project the same distance in the direction towards the center  2   l  of the oil scraper ring  1 , so that both end faces  2   d ,  2   f  can lie at the surface  6   a  of the piston ring  6 . In a particularly advantageous embodiment the material forming the first end face  2   d  is a material with very good dry running properties, such as a filled PTFE or a high temperature polymer modified with filling materials suitable for the dry running, such as PTFE, MoS2, graphite etc. The first and second end face  2   d ,  2   f  are mutually separated via a groove  2   b  extending in the circumferential direction  2   x .  FIG. 10  moreover shows a passage  2   c  running in a radial direction which passage is laterally bounded by the crown part  2   i . The oil scraper ring  2  has a long crown part  2   p  which in the illustrated embodiment extends over the three segments and over an angle and/or a length A of more than 180 degrees. 
     In a further embodiment the second end face  2   f , as illustrated in  FIG. 10  in a dotted manner and referred to with recessed end face  2   e , can be arranged set back so that an intermediate space  2   q  is formed between the recessed end face  2   e  and the surface  6   a.    
       FIG. 12  shows the holding ring segment  2   a  with its groove  2   b  as well as the first and second end faces  2   d ,  2   f  again in detail. The holding ring segment  2   a  further has a recess  2   k  for the reception of the clamping element  4 . The groove  2   b  has an extent towards the center  2   l , in the illustrated embodiment, in which extent the groove  2   b  has a support surface  2   h  running transverse or oblique to the surface  6   a  of the piston rod  6  which support surface, as illustrated in  FIG. 10 , is arranged and configured such that this serves as a support for the scraper  3 . 
       FIG. 13  shows a further embodiment of a holding ring segment  2   a  which could be suitable for an oil scraper ring  2  illustrated in  FIG. 11 . The holding ring segment  2   a  has an inner radius R. 
       FIG. 14  shows a section through the scraper ring segment  3   e  illustrated in Detail in  FIG. 10 . The scraper ring segment  3   e  comprises a scraper lip  3   a , a support surface  3   d , as well as a contact position  3   c  which is determined for the contact at the piston rod  6 . The scraper ring segment  3   e  preferably is composed of metal so that the contact position  3   c  is preferably configured as a sharp scraping edge. 
       FIG. 15  shows the scraper  3  already illustrated in  FIGS. 10, 11 and 14  in a perspective view. The oil scraper ring  2  in accordance with the invention has the advantage that the contact position  3   c  of the scraper  3  preferably brings about no or only a small force acting on the surface  6   a  of the piston rod  6 , since forces acting towards the center  2   l  brought about by the spring  4  can be transferred substantially or completely via the first end face  2   d  and the possibly present second end face  2   f  onto the surface  6   a  of the piston rod  6 . The scraper  3  can thus be configured such that this is optimized for an as high as possible scraping effect. In particular the cross-section of the scraper ring or respectively its dimension in radial and/or axial direction can be reduced to a minimum whereupon, also on use of a metal, a good matching of the individual segments to the piston rod  6  results. For maintaining the scraping function with increasing wear, the scraper ring is composed of at least two preferably three segments  3   e  having an abutment  3   b  with play dimensioned for the desired wear. The oil scraper ring  2  can be of one piece design or of multi piece design, preferably of three piece design and likewise includes an abutment  2   g  with play for wear compensation. To avoid oil leakages by the abutments  2   g ,  3   b  the oil scraper ring  2  and the scraper  3  are arranged such that they seal one another against the abutments  2   g ,  3   b  and thus no continuous leak-age paths are present in the running direction of the piston rod  6 . In this way a good scraping effect is ensured also on increasing wear. 
       FIG. 19  shows a further embodiment of an oil scraper ring  2  which in contrast to the embodiment illustrated in  FIG. 11  is of one piece design having a single abutment position  2   g . Otherwise, the oil scraper ring  2  is configured as illustrated in  FIG. 11  and thus also has the cross-section illustrated in  FIG. 10 . 
       FIG. 18  shows a further embodiment of an oil scraper ring  2  in section which, in contrast to the embodiment illustrated in  FIG. 10 , has no support surface  2   h , since the scraper  3  extends point-like to the center  2   l  and forms the contact position  3   c  at its tip. The passage  2   c  can, as illustrated by way of example in  FIG. 18 , also be configured as a covered passage  2   r  so that the covered passage  2   r  forms a through opening. 
       FIG. 16  shows a horizontally running oil scraper ring package comprising three oil scraper rings  2  arranged behind one another in the direction of extent  6   b  of the piston rod  6 .  FIG. 17  shows a front view from the direction B of the oil scraper ring  2  arranged in  FIG. 16 . As illustrated in  FIG. 17 , the recessed end face  2   e  is, as also illustrated by dots in  FIG. 10 , arranged set back, so that an intermediate space  2   q  is formed at least between the long crown part  2   p  and the surface  6   a  of the piston rod  6 . The first end face  2   d  as well as the contact surface  3   c  of the scraper lip  3   a  of the scraper  3  lie at the surface  6   a  of the piston rod  6 , so that oil is scraped which, as illustrated by the fluid flow  8 , escapes via the passages  2   c  radially outwardly. The passages  2   c  are arranged at the bottom in the circumferential direction at least along an angular range of 60 degrees, wherein a respective crown part  2   i  is arranged between two passages  2   c . Advantageously each passage  2   c  has a width corresponding to an angular range of at least 10 degrees in the circumferential direction  2   x , so that each passage  2   c  extends over an angular range of at least 10 degrees in the circumferential direction  2   x . At the top a, for example, semicircular long crown part  2   p  is arranged between the passages  2   c  arranged between the left and the right, which long crown part  2   p  extends over an angular range of at least 60 degrees, wherein this long crown part  2   p  is configured continuously in the circumferential direction, such that the crown part  2   p  has no opening. This design has the advantage that the scraped oil, as illustrated by the fluid flow  8 , can only escape downwardly, since the oil scraper arrangement  1  has no continuous passage  2   c  towards the top in the radial direction. In a particularly advantageous embodiment the oil scraper arrangement  1  arranged beside one another, as illustrated in  FIG. 16 , have a security against rotation, for example, a fixing pin  5 , in order to prevent a rotation of the oil scraper arrangement  1  with respect to one another and in order to preferably also prevent a rotation of the oil scraper arrangement  1  with respect to the housing  7 . 
     The oil scraper ring  2  in accordance with the invention, as illustrated in  FIGS. 16 and 17 , has the advantage that the drainage passages formed by the intermediate spaces  2   q  are not switched downstream but upstream of the scraper  3  from the direction B, so that a continuous planar surface is formed in the circumferential direction towards a compressor piston  6   d . This surface acts as a sealing surface and thus prevents the exit of lubricant in the direction of extent of the piston rod  6  from the respective oil scraper ring  2 . Furthermore, as illustrated in  FIG. 16 , advantageously no drainage passages are arranged in the direction opposing the gravity for the use in a horizontal arrangement. The scraped oil is thus, as illustrated in  FIG. 17 , only guided laterally and downwardly. In this way an overflow of the individual scrapers  3  or of the individual oil scraper rings  2  respectively is prevented. Advantageously, the fixing pins  5  further ensure that the scraper  3  is installed in the correct position with the sealed passages towards the top. 
       FIG. 19  shows a top view onto a further embodiment of an oil scraper ring  2  of one part design. The oil scraper ring  2  illustrated in  FIG. 16  has a continuous crown part  2   p  which extends over an angular range A which can extend over an angle of between 60 degrees and 350 degrees. In the illustrated embodiment the radially running abutment position  2   g  extends through the crown part  2   p . The abutment part  2   g  can, however, also be arranged such that this is not arranged in the angular range A and for this reason does not extend through the crown part  2   p.