Engine exhaust valve stem seal for high temperature and pressure applications

Abstract

An exhaust valve stem seal assembly includes a casing and an elastomeric seal coupled to the casing. The elastomeric seal includes a stem seal portion for sealing against a stem of an exhaust valve. The stem seal portion includes a gas lip that extends radially inward. The casing includes a frustoconical shoulder extending radially inward toward a valve axis to a distal edge. The frustoconical shoulder defines an angle relative to a plane perpendicular to the valve axis between the range of 5° and 45°. The distal edge of the frustoconical shoulder is disposed behind and is substantially aligned with the gas lip along the valve axis.

1 . A seal assembly for an exhaust valve stem of an engine, the seal assembly comprising:
 a casing having an annular body portion extending between a first axial end and a second axial end along a valve axis, and defining an interior;   an elastomeric seal coupled to the casing and including a guide seal portion disposed within the interior of the annular body portion for engaging a valve guide, a stem seal portion extending away from the casing and the second axial end of the annular body portion along the valve axis for engaging a valve stem, and a shoulder portion interconnecting the guide seal portion and the stem seal portion;   wherein the stem seal portion includes a gas lip extending radially inward toward the valve axis and toward the first axial end of the annular body portion, and defines a void between the gas lip and the shoulder portion of the elastomeric seal; and   wherein the casing includes a frustoconical shoulder extending from the second axial end of the annular body portion radially inward toward the valve axis and away from the first axial end of the annular body portion to a distal edge.   
     
     
         2 . A seal assembly as set forth in  claim 1  wherein the distal edge of the frustoconical shoulder is substantially aligned with the gas lip along the valve axis. 
     
     
         3 . A seal assembly as set forth in  claim 2  wherein the distal edge of the frustoconical shoulder is within an axial distance of the gas lip along the valve axis, and wherein the axial distance is equal to twice a distance between a lower edge of the gas lip and an upper edge of the void as measured along the valve axis. 
     
     
         4 . A seal assembly as set forth in  claim 1  wherein a cross section of the frustoconical shoulder is substantially disposed along a plane, and wherein the plane of the cross section of the frustoconical shoulder defines an angle relative to a plane perpendicular to the valve axis between the range of 5° and 45°. 
     
     
         5 . A seal assembly as set forth in  claim 1  wherein the frustoconical shoulder is configured to allow the stem seal portion of the elastomeric seal to rotate radially outward away from the valve axis and axially away from the first axial end of the annular body portion of the casing to maintain a substantially constant pressure and contact width between the gas lip and the valve stem in response to thermal expansion of the elastomeric seal. 
     
     
         6 . A seal assembly as set forth in  claim 1  wherein the distal edge of the frustoconical shoulder is spaced from the first axial end of the annular body a distance equal to or less than a distance between a base of the gas lip and the first axial end of the annular body. 
     
     
         7 . A seal assembly as set forth in  claim 1  wherein the casing includes and is manufactured from a metal. 
     
     
         8 . A seal assembly as set forth in  claim 1  wherein the elastomeric seal includes and is manufactured from an elastomer. 
     
     
         9 . An exhaust valve stem seal assembly for an engine, the exhaust valve stem seal assembly comprising:
 a casing having an annular body portion extending between a first axial end and a second axial end along a valve axis, and defining an interior;   an elastomeric seal coupled to the casing and including a guide seal portion disposed within the interior of the annular body portion for engaging a valve guide, a stem seal portion extending away from the casing and the second axial end of the annular body portion along the valve axis for engaging a valve stem, and a shoulder portion interconnecting the guide seal portion and the stem seal portion;   wherein the stem seal portion includes a gas lip extending radially inward toward the valve axis and toward the first axial end of the annular body portion, and defines a void between the gas lip and the shoulder portion of the elastomeric seal;   wherein the casing includes a frustoconical shoulder extending from the second axial end of the annular body portion radially inward toward the valve axis and away from the first axial end of the annular body portion to a distal edge;   wherein the distal edge of the frustoconical shoulder is substantially aligned with the gas lip along the valve axis; and   wherein the frustoconical shoulder defines an angle relative to a plane perpendicular to the valve axis between the range of 5° and 45°.   
     
     
         10 . An exhaust valve stem seal assembly as set forth in  claim 9  wherein the distal edge of the frustoconical shoulder is within an axial distance of the gas lip along the valve axis, and wherein the axial distance is equal to twice a distance between a lower edge of the gas lip and an upper edge of the void as measured along the valve axis. 
     
     
         11 . An exhaust valve stem seal assembly as set forth in  claim 10  wherein the frustoconical shoulder is configured to allow the stem seal portion of the elastomeric seal to rotate radially outward away from the valve axis and axially away from the first axial end of the annular body portion of the casing to maintain a substantially constant pressure and contact width between the gas lip and the valve stem in response to thermal expansion of the elastomeric seal.