Abstract:
In some two-stroke engines, a stationary ring is disposed in a groove in the cylinder liner. However, it is a challenge to install such a stationary ring while maintaining a narrow gap to minimize gas flow through the gap. A ring system for an internal combustion engine is disclosed that includes an L-shaped, split ring with a reentrant angle and a nested, split ring with a convex quadrilateral cross section nested with the L-shaped ring proximate the reentrant angle. The two rings are affixed so that the two gaps of the split rings cannot align. Or, in other embodiments, the two are allowed to rotate relative to each other over a predetermined angle.

Description:
FIELD 
       [0001]    The present disclosure relates to stationary rings for devices that have reciprocating pistons, such as internal combustion engines and compressors. 
       BACKGROUND 
       [0002]    Pistons in two-stroke engines have compression rings like their four-stroke counterparts. Some two-stroke engines that have ports in the cylinder wall, which are covered and uncovered by a piston, have an additional oil ring in the piston that is below the ports. The oil ring prevents oil that is splashing around for lubrication and cooling from too much access to the ports and being combusted in the combustion chamber or leaving directly through exhaust ports. The oil ring also provides oil dosing, to allow some oil to lubricate the compression rings and the piston skirt. In addition, the oil ring in a two-stroke engine has to seal the pressurized air at the intake ports or the exhaust gas at the exhaust ports from escaping into the crankcase. Such an arrangement leads to a piston or liner that is longer than may desirable for some applications. An alternative is to provide a sealing ring (stationary ring) in a groove in the cylinder wall such as is shown in  FIGS. 1   a - c.    
         [0003]    In  FIG. 1   a , a piston  10  having compression rings  12  and  14  is traveling downward within a cylinder wall  20  (only a portion of one side of the wall is shown in the cross section in  FIG. 1   a ) that has ports  22  in the wall to allow flow of gases into the cylinder, if the ports are intake ports, and flow of gases out of the cylinder, if the ports are exhaust ports. A circumferential groove is formed in cylinder wall  20  into which a stationary oil ring  24  is placed. In  FIG. 1   a , piston  10  is in a position such that compression rings  12  and  14  are above port  22 . Thus, the combustion chamber (above piston  10 ) is sealed off from port  22 . Piston  10  is moving downward and at the instant illustrated in  FIG. 1   b , port  22  is in communication with the combustion chamber. As piston  10  moves downward farther, as illustrated in  FIG. 1   c , piston  10  completely uncovers port  22 . 
         [0004]    A view of a piston  370  in a cylinder liner  368  is shown in  FIG. 13 . Piston  370  has compression rings  374 . Cylinder liner  368  has ports  376  and a groove  372  defined there. A stationary ring may be installed in groove  372  to assist with oil and/or gas control. 
         [0005]    Cylinder wall  20  in  FIGS. 1   a - c  is shown as one piece. However, stationary oil ring  24 , which is a split ring, has a large gap if inserted into cylinder wall  20  and then sprung into the groove in the cylinder liner. In some alternatives, the cylinder wall is formed out of two pieces. In  FIG. 1   c , a dotted line  26  in cylinder wall  20  indicates a parting line that can be used in a two-piece cylinder liner to facilitate installation of stationary oil ring  24 . Problems with two-piece cylinder liners include: increased weight to include a flange and bolts to secure the two pieces together and difficulty in ensuring that the cylinder walls of the two pieces are perfectly aligned and machined properly. A ring system that facilitates installation into a one-piece cylinder liner is desired. 
       SUMMARY 
       [0006]    To overcome at least one problem with prior art systems, a ring system that can be used in a device having a reciprocating piston, such as an internal combustion engine or a compressor, includes an L-shaped, split ring with a reentrant angle; a nested, split ring with a convex quadrilateral cross section nested with the L-shaped ring proximate the reentrant angle; and a feature between the L-shaped and nested rings that limits relative, rotational movement between the rings to less than a predetermined angle wherein the L-shaped and nested rings are adapted to be installed into a groove in a cylinder wall of the device. 
         [0007]    In one embodiment, the feature is a pin and the predetermined angle is substantially zero. In another embodiment, the feature is one of a weld and braze joint and the predetermined angle is substantially zero. In yet another embodiment, a groove is formed in a predetermined angle of the circumference of one of the L-shaped ring and the nested ring proximate the reentrant angle and a tab is formed in the other of the L-shaped ring and the nested ring. The tab engages with the groove. The tab is the feature that limits relative rotational movement between the rings with the predetermined angle being less than 160 degrees. 
         [0008]    The ring system may further include a groove in a surface of the L-shaped ring located in a wall of the L-shaped ring proximate a surface of the groove in the cylinder wall and a continuous ring inserted in the groove in the L-shaped ring. 
         [0009]    A gap in the L-shaped ring and a gap in the nested ring are circumferentially displaced from each other to reduce gas flow between first and second sides of the L-shaped and nested rings. 
         [0010]    Also disclosed is a piston-and-cylinder assembly having a cylinder wall having a groove formed therein, a piston disposed within the cylinder wall, an L-shaped, split ring with a reentrant angle disposed in the groove, and a nested, split ring with a convex quadrilateral cross section nested with the L-shaped ring proximate the reentrant angle. In some embodiments, the L-shaped and nested rings are affixed by one of pinning, welding, and brazing to prevent relative, rotational movement between the rings. The piston is adapted to reciprocate within the cylinder wall. Surfaces of the L-shaped and nested rings proximate the piston form an acute angle with respect to a surface of the piston. 
         [0011]    The L-shaped and nested rings bear on the piston surface. The L-shaped and nested rings are adapted to scrape oil from the piston surface. The assembly is part of one of an internal combustion engine or a compressor. 
         [0012]    Some embodiments include: a groove defined in a surface of the L-shaped ring in a wall of the L-shaped ring proximate a surface of the groove in the cylinder wall and a continuous ring element inserted in the groove in the L-shaped ring. Continuous refers to a ring without a split. 
         [0013]    A gap in the L-shaped ring and a gap in the nested ring are circumferentially displaced from each other to reduce gas flow between first and second sides of the L-shaped and nested rings. 
         [0014]    A diameter of an outer surface of the L-shaped ring is greater than a diameter of the cylinder wall when the L-shaped ring is in its neutral position. When the L-shaped ring is contracted so that the L-shaped ring has a diameter substantially equal to the diameter of the cylinder wall, the gap in the split ring is nearly zero. When the L-shaped ring is expanded to allow insertion of the piston into the L-shaped ring and then released, the L-shaped ring presses against the piston. 
         [0015]    Also disclosed is a method to install a ring system, including: nesting an L-shaped ring and a nested ring. The L-shaped ring is a split ring with a reentrant angle. The nested ring has a convex quadrilateral cross section. The L-shaped ring nests with the nested ring proximate the reentrant angle. The method may further include: compressing the L-shaped and nested rings; inserting the compressed rings into a cylinder liner; and moving the compressed rings into a groove in the cylinder liner whereby the compressed rings attain a neutral position in the groove. The method further includes: expanding the compressed rings such that they expand into the groove in the cylinder and inserting the piston inside the expanded rings. 
         [0016]    In some embodiments, the method also includes affixing the L-shaped ring and the nested ring by one of: pinning, brazing, or welding. 
         [0017]    In some embodiments, a circumferential groove is formed in the L-shaped ring proximate the reentrant angle. The circumferential groove extends over only a portion of the L-shaped ring. A tab is formed on an outer surface of the nested ring. The tab engages with the circumferential groove in the L-shaped ring. 
         [0018]    In some embodiment, a groove is formed in a surface of the L-shaped ring in a wall of the L-shaped ring proximate a surface of the groove in the cylinder wall. An elastomeric or metallic continuous element may be inserted in the groove in the L-shaped ring. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIGS. 1   a - c  are cross-sectional views through the cylinder liner of a portion of a piston-ported engine; 
           [0020]      FIG. 2  is a cross-sectional view of a section of the piston and cylinder liner with an L-shaped ring and a nested ring in a groove in the cylinder liner; 
           [0021]      FIG. 2   a  is a detail of a portion of the L-ring, the groove in the L-ring, and the sealing element disposed in the groove. 
           [0022]      FIGS. 3-8  are cross sections of embodiments of the L-shaped and nested rings: 
           [0023]      FIGS. 9-12  are cross sections of a cylinder liner illustrating steps to install the L-shaped and nested rings; 
           [0024]      FIG. 13  is a cross section of a portion of a piston-ported engine showing a groove into which a stationary ring may be disposed; and 
           [0025]      FIG. 14  is a flowchart indicating assembly of the engine with the stationary rings according to an embodiment of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
         [0027]    In  FIG. 2 , a cross section of a ring system or ring assembly according to an embodiment of the disclosure is shown. A portion of a piston  100  is shown proximate a portion of a cylinder liner  102  in cross section. A surface  96  of liner  102  is displaced from a surface  98  of piston  102  by a gap  101 . To substantially prevent gases flowing through gap  101 , a split ring or, in this case a pair of split rings  110  and  112  are provided. The rings are provided in a groove  103  that has an end surface  104  a bottom surface  106  and a top surface  108 . Split ring  110  has a groove in a surface proximate bottom surface  106  of groove  103 . A ring  113  is placed in the groove. A detail of split ring  110  and ring  114  is shown in  FIG. 2   a . A groove  114  in ring  110  has a metallic ring that is mostly circular in cross section, but has a split.  FIG. 2   a  is an illustration of one exemplary embodiment and is not intended to be limiting. 
         [0028]    In  FIG. 3 , split rings  110  and  112  are shown in more detail. Ring  110  is roughly L shaped with surfaces  118 ,  120 ,  122 ,  124 ,  126 , and  128 . Surfaces  124  and  126  form the interior of the L and are perpendicular to each other. Surfaces  118 ,  120 , and  128  are also perpendicular in relation to surfaces  124  and  126 . Surface  122 , which faces toward surface  98  of piston  100  (as assembled), has a slight angle. The intersection of surfaces  122  and  124  scrapes on surface  98  of piston  100  to remove excess oil during operation of the engine. The intersection of surfaces  122  and  124  appears as a point in  FIG. 3 , but in practice forms a small surface parallel to the wall on which it rides. Surfaces  124  and  126  are described as being perpendicular. However, in other embodiments, a different angle between the two surfaces can be used, but should match the angle formed between  134  and  136  of ring  112  that nests with L-ring  110 . 
         [0029]    For purposes of distinguishing surfaces herein, the following nomenclature is used, as shown in  FIG. 3 : L-ring  110 , nested ring  112 , outer surface of L-ring  118 , scraper surface of L-ring  122 , bottom surface of L-ring  120 , horizontal inner surface of L-ring  124 , vertical inner surface of L-ring  126 , outer surface  136  of nested ring  112 , left surface of nest ring  134 , right surface of nested ring  138 , and scraper surface of nested ring  132 . 
         [0030]    L-ring  110  has a groove  114  to accommodate a sealing member  113 , the sealing member shown in  FIGS. 2 and 2   a . An alternative L-ring  140  is shown in  FIG. 4  that has no such groove. In such an alternative, the ring may be designed to fit tighter in the groove in the cylinder liner because there is no sealing member. 
         [0031]    In  FIG. 5  a nested ring  212  that has a tab  214  is shown with tab  214  engaging in a groove in an L-ring  210 . The groove in L-ring  210  can be provided over a small portion of the circumference, e.g., 5 degrees. In another alternative, the groove could be provided over 135 degrees. A greater range is undesirable as it would allow the gaps in nested ring  212  and L-ring  210  (gaps not visible in  FIG. 5 ) to align, which would allow gases to easily flow past the ring assembly. A groove  216  in L-ring  210  is visible in  FIG. 6 . There may be advantages to allow the rings to rotate with respect to each other to prevent buildup of deposits and potential ring sticking. 
         [0032]    In an alternative, L-ring  140  and nested ring  112  are pinned together with a pin  142  by first providing a hole in each and then inserting pin  142 . When the pin is installed and then the ring is installed with the groove in the cylinder wall, the pin does not back out because it would hit a wall of the groove in the cylinder wall. In an alternative shown in  FIG. 8 , a pin  144  is installed through an orifice that extends through nested ring  112  and L-ring  140 . To ensure that pin  144  does not fall out, a plug  146  is installed in a countersunk hole in nested ring  112 . 
         [0033]    The assembly of an engine with such a ring pack is described in conjunction with  FIGS. 9-12 .  FIGS. 9-12  exaggerate the sizes of the nested and L-shaped rings for illustration purposes only.  FIG. 9  shows a cross section of cylinder wall  102  as taken through groove  103 . The center of cylinder wall  102  is identified as 90. Groove  103  extends through the inside surface  98  of the cylinder wall to the inside surface  96  of the groove. 
         [0034]    In  FIG. 10 , split rings  110  and  112  are compressed so that they fit within the inside surface  98  of cylinder wall  102  so that split rings  110  and  112  can be slid into cylinder wall  102  to the area where groove  103  is located. When compressed, the ends of rings  110  and  112  are touching, shown as splits  146  and  148 , respectively. 
         [0035]    In  FIG. 11 , split rings  110  and  112  are allowed to expand to their neutral position, which is only possible within groove  103 . Splits  142  and  144  are noticeable in rings  110  and  112 , respectively, as the rings expand. In one non-limiting embodiment, splits  142  and  144  include about 10 degrees of circumference. 
         [0036]    In  FIG. 12 , split rings  142  and  144  are expanded, in one embodiment via a special tool, so that they have splits  150  and  152 , respectively, which are, in a non-limiting embodiment, about 20 degrees of the circumference. Piston  100  is inserted into the cylinder so that split rings  110  and  112  remain expanded such that they tend toward the neutral position and consequently exert a force on the piston to scrape oil off the piston. 
         [0037]    In  FIGS. 10-12 , the gap (or touching ends in  FIG. 10 ) in split rings  110  and  112  are substantially diametrically opposed to each other. It is not imperative that they are evenly spaced. However, it is important that they not overlap or come close to overlapping. If the cross section in  FIG. 2  were taken through the split in L-ring  110  in a region of the gap in L-ring  110 , nested ring  112  would provide sealing. If the cross section in  FIG. 1  were taken through the split in nested ring  112  in a region of the gap in nested ring  112 , L-ring would provide the sealing. But, this is only the case if alignment of the gaps in the two rings can be prevented, which is accomplished by an arrangement such as: tab  214  in  FIG. 5 , pin  142  in  FIG. 7 , pin  144  in  FIG. 8 , or other suitable engagement feature. 
         [0038]    Referring to the flowchart in  FIG. 14 , the L-shaped and nested rings are fabricated in block  300 . This includes any machining to cause the two to fit together as desired. The two are pinned together in block  310 . In an alternate embodiment, a pin in one of the rings extends into a groove in the other of the rings such that the rings are engaged. The rings are allowed to rotate with respect to each other, but are limited to a particular predetermined range with the range limited by the extent of the groove in the ring. In block  320 , a groove is formed into a one-piece cylinder liner. In block  330 , the ring assembly from block  310  is inserted into the cylinder liner. In block  330 , the ring assembly is compressed to be a smaller diameter (less than or equal to the cylinder liner diameter) than its neutral position so that it can be inserted into the cylinder liner. In block  340 , the ring assembly is slid to the groove in the cylinder liner and allowed to expand to its neutral position, i.e., fitting into the groove. In block  350 , the ring assembly is expanded such that more of the ring assembly is within the cylinder liner groove. This may be accomplished with a special tool or, alternatively, by a chamfer on the piston skirt. A piston is inserted into the cylinder liner and within the expanded ring assembly in block  360 . When the ring assembly is released from the expanded position, it does not contract to its neutral position but instead exerts a force on the outer surface of the piston. 
         [0039]    While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.