Piston Ring for Reduction of Crevice Volume

Abstract

Embodiments of a piston ring reduce the volume of a crevice defined between the circumferential wall of a cylinder and a portion of the outer wall of a piston within the cylinder, the portion extending down from the top of the piston. The piston ring is configured such that pressurized fluid within the cylinder reliably urges a radial face of the piston ring to sealingly engage the circumferential wall of the cylinder, even as the piston reciprocates within the cylinder.

What is claimed is: 
     
         1 . A piston ring for sealing a gap between a circumferential surface of a piston ( 150 ) of a reciprocating machine and a wall ( 111 ) of a cylinder of the machine within which the piston reciprocates along an axis, the piston ring comprising:
 an upper member ( 210 ) configured to reside in a peripheral corner cut-out ( 153 ) of the piston, the upper member having:
 (i) a radial contact surface ( 211 ) configured to be radially loaded against the cylinder wall ( 111 ) during operation of the reciprocating machine, 
 (ii) at least one fluid-pressure receiving surface ( 212 ,  213 ), and 
 (iii) an inner axial contact surface ( 214 ) configured to contact a ridge ( 170 ) of the piston, when the at least one fluid-pressure receiving surface ( 212  and  213 ) is axially loaded by fluid pressure; 
   wherein the radial contact surface and the at least one fluid-pressure receiving surface are shaped so that the fluid pressure causes a net force by which the radial contact surface is urged radially against the cylinder wall and the inner axial contact surface is urged axially against the piston.   
     
     
         2 . The piston ring according to  claim 1 , wherein the piston ring further includes at least one retaining feature ( 220 ,  224 ,  225 ) extending from the upper member, and configured to maintain positioning of the upper member during the downward intake stroke of the piston. 
     
     
         3 . The piston ring according to  claim 1  further comprising:
 a lower member ( 220 ) having an inner axial contact surface ( 221 ) that during a downward motion of the piston is configured to contact the ridge of the piston; and 
 a bridge ( 230 ) coupling the upper member to the lower member, and spanning an axial distance downwardly from the upper member to the lower member. 
 
     
     
         4 . The piston ring according to  claim 3 , further comprising a secondary seal ( 206 ) disposed radially inward from the bridge, so that the secondary seal is configured to be loaded against the piston or the bridge by pressure of any fluid that has blown by the inner axial contact surface. 
     
     
         5 . The piston ring according to  claim 1 , wherein the radial contact surface has a parabolic profile. 
     
     
         6 . A piston ring for sealing a gap between a circumferential surface of a piston ( 150 ) of a reciprocating machine and a wall ( 111 ) of a cylinder of the machine within which the piston reciprocates along an axis, the piston ring comprising:
 a circumferential member ( 210 ) configured to reside in a peripheral corner cut-out ( 153 ) of the piston, the circumferential member having:
 (i) a radial contact surface ( 211 ) configured to be radially loaded against the cylinder wall ( 111 ) during operation of the reciprocating machine, and 
 (ii) at least one fluid-pressure receiving surface ( 212 ,  213 ) 
   
       wherein a projection ( 293 ) of the at least one fluid-pressure receiving surface ( 212 ,  213 ) onto the wall of the cylinder is greater than a projection ( 291 ) of the radial contact surface ( 211 ) onto the wall of the cylinder. 
     
     
         7 . The piston ring according to  claim 6 , wherein the radial contact surface has a parabolic profile. 
     
     
         8 . The piston ring according to  claim 6 , further comprising:
 a lower member ( 220 ) having an inner axial contact surface ( 221 ) that during a downward motion of the piston is configured to contact the ridge of the piston; and   a bridge ( 230 ) coupling the upper member to the lower member, and spanning an axial distance downwardly from the upper member to the lower member.   
     
     
         9 . The piston ring according to  claim 8 , further comprising a secondary seal ( 206 ) disposed radially inward from the bridge, so that the secondary seal is configured to be loaded against the piston or the bridge by pressure of any fluid that has blown by the inner axial contact surface. 
     
     
         10 . The piston ring according to  claim 6 , wherein the piston ring further includes at least one retaining feature ( 220 ,  224 ) extending from the upper member, and configured to maintain positioning of the upper member during a downward intake stroke of the piston. 
     
     
         11 . A piston ring for sealing a gap between a circumferential surface of a piston ( 150 ) of a reciprocating machine and a wall of a cylinder ( 110 ) of the machine within which the piston reciprocates along an axis, the piston ring comprising:
 means for substantially filling a crevice between a top region of the piston and the wall ( 111 ) of the cylinder, and having
 (i) a radial contact surface ( 211 ), and 
 (ii) at least one fluid-pressure receiving surface ( 212 ,  213 ); and 
   means for securing the piston ring in a peripheral corner cut-out of the piston;   wherein the radial contact surface and the at least one fluid-pressure receiving surface are shaped so that fluid pressure causes a net force by which the radial contact surface is urged radially against the cylinder wall.   
     
     
         12 . The piston ring according to  claim 11 , wherein a first area of a projection ( 293 ) of the at least one fluid-pressure receiving surface ( 212 ,  213 ) onto the wall of the cylinder is greater than a second area of a projection ( 291 ) of the radial contact surface ( 211 ) onto the wall of the cylinder. 
     
     
         13 . The piston ring according to  claim 11 , wherein the means for securing the piston ring in the peripheral corner cut-out of the piston comprises a plurality of teeth ( 225 ) extending radially inward from the interior fluid-pressure receiving surface ( 213 ) and configured to interlock with a retaining groove in the piston. 
     
     
         14 . The piston ring according to  claim 11 , wherein the means for securing the piston ring in the peripheral corner cut-out of the piston comprises a plurality of L-shape tabs, each such tab comprising:
 a stem ( 281 ) extending axially from the means for substantially filling the crevice; and   a digit ( 282 ) extending radially inward from the stem ( 281 ) and configured to interlock with a retaining groove ( 175 ) in the piston.   
     
     
         15 . The piston ring according to  claim 11 , wherein the means for securing the piston ring in the peripheral corner cut-out of the piston comprises a plurality of T-shaped tabs, each tab comprising:
 a stem ( 296 ) extending axially from the means for substantially filling the crevice; and   a crossbar ( 297 ) extending from the stem ( 296 ) and configured to interlock with a retaining groove ( 175 ) in the piston.   
     
     
         16 . A piston ring for sealing a gap between a circumferential surface of a piston ( 150 ) of a reciprocating machine and a wall ( 111 ) of a cylinder of the machine within which the piston reciprocates along an axis, the piston ring comprising:
 an upper member ( 210 ) configured to reside in a cut-out of the piston, the upper member having:
 (i) a radial contact surface ( 211 ) configured to be radially loaded against the cylinder wall ( 111 ) during operation of the reciprocating machine, 
 (ii) at least one fluid-pressure receiving surface ( 212 ,  213 ), and 
 (iii) an inner axial contact surface ( 214 ) configured to contact a ridge ( 170 ) of the piston, when the at least one fluid-pressure receiving surface ( 212  and  213 ) is axially loaded by fluid pressure; 
   a bridge spanning an axial distance downwardly from the upper member; and   a secondary seal disposed radially inward from the bridge,   wherein the radial contact surface and the at least one fluid-pressure receiving surface are shaped so that the fluid pressure causes a net force by which the radial contact surface is urged radially against the cylinder wall and the inner axial contact surface is urged axially against the piston, and the secondary seal is configured to be loaded against the piston or the bridge by pressure of any fluid that has blown by the inner axial contact surface.