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.degree. and 45.degree.. The distal edge of the frustoconical shoulder is disposed behind and is substantially aligned with the gas lip along the valve axis.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/592,174, filed on Jan. 30, 2012, the disclosure of which is hereby incorporated by reference.

TECHNICAL FIELD

[0002] The invention generally relates to an exhaust valve stem seal assembly for an internal combustion engine.

BACKGROUND

[0003] In some internal combustion engines, a valve guide is positioned within a cylinder head of an internal combustion engine to guide an exhaust valve in reciprocating motion. The valve guide supports and guides a stem of the exhaust valve for axially movement along a valve axis. Clearance is provided between the valve guide and the exhaust valve stem in order to allow free movement between the valve guide and the exhaust valve stem. A stem seal assembly is coupled to the valve guide and seals against the stem of the exhaust valve to prevent combustion gases from escaping through the clearance between the exhaust valve stem and the valve guide. The exhaust valve stem seal assembly further meters oil into the valve guide to lubricate between the valve stem and the valve guide.

[0004] The stem seal assembly is generally comprised of a steel casing supporting an elastomeric seal. The elastomeric seal expands when subjected to high temperatures and high exhaust gas pressures. This thermal expansion of the elastomeric seal reduces the ability of the elastomeric seal to maintain oil flow to the valve guide, which may result in excessive wear of the valve guide.

SUMMARY

[0005] A seal assembly for an exhaust valve stem of an engine is provided. The seal assembly includes a casing having an annular body portion that extends between a first axial end and a second axial end along a valve axis. The annular body portion further defines an interior. An elastomeric seal is coupled to the casing. The elastomeric seal includes a guide seal portion, a stem seal portion, and a shoulder portion. The guide seal portion is disposed within the interior of the annular body portion for engaging a valve guide. The stem seal portion extends away from the casing and the second axial end of the annular body portion along the valve axis for engaging a valve stem. The shoulder portion interconnects the guide seal portion and the stem seal portion adjacent the second axial end of the annular body portion. The stem seal portion includes a gas lip that extends radially inward toward the valve axis and toward the first axial end of the annular body portion. A void is defined between the gas lip and the shoulder portion of the elastomeric seal. The casing includes a frustoconical shoulder extending from the second axial end of the annular body portion to a distal edge of the frustoconical shoulder. The frustoconical shoulder extends radially inward toward the valve axis and away from the first axial end of the annular body portion.

[0006] An exhaust valve stem seal assembly for an engine is provided. The exhaust valve stem seal assembly includes a casing having an annular body portion extending between a first axial end and a second axial end along a valve axis. The annular body portion defines an interior. An elastomeric seal is coupled to the casing. The elastomeric seal includes a guide seal portion, a stem seal portion and a shoulder portion. The guide seal portion is disposed within the interior of the annular body portion for engaging a valve guide. The stem seal portion extends away from the casing and the second axial end of the annular body portion along the valve axis for engaging a valve stem. The shoulder portion interconnects the guide seal portion and the stem seal portion. The stem seal portion includes a gas lip that extends radially inward toward the valve axis and toward the first axial end of the annular body portion. A void is defined between the gas lip and the shoulder portion of the elastomeric seal. The casing includes a frustoconical shoulder that extends from the second axial end of the annular body portion to a distal edge. The frustoconical shoulder extends radially inward toward the valve axis and away from the first axial end of the annular body portion to the distal edge. The distal edge of the frustoconical shoulder is substantially aligned with the gas lip along the valve axis. The frustoconical shoulder defines an angle relative to a plane that is perpendicular to the valve axis between the range of 5.degree. and 45.degree..

[0007] Accordingly, the frustoconical shoulder of the casing angles from the annular body portion of the casing toward the gas lip, and extends from the second axial end of the annular body portion to the distal edge of the frustoconical shoulder, which is located immediately behind the gas lip. As such, as the stem seal portion of the elastomeric seal expands in response to high temperatures and high pressure, the distal edge of the frustoconical shoulder acts as a hinge or pivot point to allow the stem seal portion of the elastomeric seal to expand and rotate away from the stem of the exhaust valve, thereby maintaining the proper shape and configuration of the gas lip and preventing the void located behind the gas lip from collapsing. By maintaining the proper shape and configuration of the gas lip, and by preventing the void from collapsing, lubricating oil may be properly metered past the gas lip into the clearance between the valve guide and the exhaust valve stem for lubrication therebetween.

[0008] The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a schematic partial cross sectional view of an exhaust valve stem seal assembly sealing against a valve stem supported by a valve guide.

[0010] FIG. 2 is a schematic cross sectional view of the exhaust valve stem seal assembly.

[0011] FIG. 3 is a schematic enlarged fragmentary cross sectional view of the exhaust valve stem seal.

DETAILED DESCRIPTION

[0012] Those having ordinary skill in the art will recognize that terms such as "above," "below," "upward," "downward," "top," "bottom," etc., are used descriptively for the figures, and do not represent limitations on the scope of the invention, as defined by the appended claims.

[0013] Referring to the Figures, wherein like numerals indicate like parts throughout the several views, a seal assembly is generally shown at 20. The seal assembly 20 may be referred to as an exhaust valve stem seal assembly 20.

[0014] Referring to FIG. 1, a valve guide 22 is disposed within a bore 23 of a cylinder head 24. The valve guide 22 defines a central bore 25 that slideably supports a stem 26 of an exhaust valve 28 for reciprocating movement along a valve axis 30. The valve axis 30 is located along a longitudinal center of the stem 26. The seal assembly 20 is coupled or attached to the valve guide 22.

[0015] Referring also to FIGS. 2 and 3, the seal assembly 20 includes a casing 32 supporting an elastomeric seal 34. The casing 32 includes an annular body portion 36 that extends along the valve axis 30 between a first axial end 38 and a second axial end 40 of the annular body portion 36. The annular body portion 36 includes a generally tubular shape and defines an interior 42. The casing 32 includes a frustoconical shoulder 44 that extends from the second axial end 40 of the annular body portion 36 to a distal edge 46. The frustoconical shoulder 44 extends radially inward toward the valve axis 30, and also extends away from the first axial end 38 of the annular body portion 36 to the distal edge 46. The frustoconical shoulder 44 includes a frustoconical shape generally defined as a cone shape with the tip of the cone removed. While the frustoconical shoulder 44 is shown to include a planar cross section, it should be appreciated that the frustoconical shoulder 44 may alternatively include a slightly curved cross sectional shape, such as but not limited to a slightly convex cross sectional shape. A flange 48 extends radially outward from the first axial end 38 of the annular body portion 36, away from the valve axis 30.

[0016] Referring to FIG. 3, the cross section of the frustoconical shoulder 44 is substantially disposed along a plane 49. The plane 49 is disposed relative to a plane 50, which is perpendicular to the valve axis 30, to define an angle 52 therebetween. The angle 52 between the plane 49 of the frustoconical shoulder 44 and the plane 50 is preferably between the range of 5.degree. and 45.degree.. The casing 32 may include and be manufactured from a metal, such as but not limited to steel. However, the casing 32 may be manufactured from some other suitable material.

[0017] The elastomeric seal 34 is coupled to the casing 32. The elastomeric seal 34 includes and is manufactured from an elastomer suitable for sealing against the valve guide 22 and the stem 26 of the exhaust valve 28 in a high temperature and high pressure environment. The elastomeric seal 34 includes a guide seal portion 54, a stem seal portion 56, and a shoulder portion 58. The guide seal portion 54 is disposed within the interior 42 of the annular body portion 36 of the casing 32. The guide seal portion 54 engages the valve guide 22 in sealing/frictional engagement therewith. The stem seal portion 56 extends away from the casing 32 and the second axial end 40 of the annular body portion 36, along the valve axis 30. Accordingly, the stem seal portion 56 extends from the second axial end 40 of the annular body portion 36 in a direction opposite the first axial end 38 of the annular body portion 36. Accordingly, the stem seal portion 56 is not radially constrained about the valve axis 30 by the casing 32, thereby allowing the stem seal portion 56 to expand radially in response to increased temperature and pressure. As shown, a garter spring clip 60 is disposed within a groove 62 defined by the stem seal portion 56 of the elastomeric seal 34 to radially bias the stem seal portion 56 against the stem 26 of the exhaust valve 28. The stem seal portion 56 engages the stem 26 of the exhaust valve 28 in sealing engagement therewith. The shoulder portion 58 interconnects the guide seal portion 54 and the stem seal portion 56, and is disposed adjacent the second axial end 40 of the annular body portion 36 of the casing 32.

[0018] As best shown in FIG. 3, the stem seal portion 56 includes a gas lip 64. The gas lip 64 seals against the stem 26 of the exhaust valve 28 to prevent gases from escaping through the interface between the valve guide 22 and the stem 26 of the exhaust valve 28. While the gas lip 64 prevents gases from escaping in a direction indicated by arrow 66, the gas lip 64 allows lubricating oil to pass in a direction opposite arrow 66, to lubricate the interface between the valve guide 22 and the stem 26 of the exhaust valve 28. The gas lip 64 extends radially inward toward the valve axis 30, and extends toward the first axial end 38 of the annular body portion 36. The gas lip 64 is spaced from the shoulder portion 58 of the elastomeric seal 34 to define a void 68 between the gas lip 64 and the shoulder portion 58.

[0019] As best shown in FIG. 3, the distal edge 46 of the frustoconical shoulder 44 is positioned to substantially align with the gas lip 64 along the valve axis 30. In other words, the distal edge 46 of the frustoconical shoulder 44 is disposed radially outward of the gas lip 64, and is disposed at approximately the same axial location along the valve axis 30 as the gas lip 64. Preferably, the distal edge 46 of the frustoconical shoulder 44 is within an axial distance of the gas lip 64 measured along the valve axis 30. The axial distance is equal to twice a distance 76 between a bottom or lower edge 78 of the gas lip 64 and a top or upper edge 80 of the void 68 as measured along the valve axis 30. Preferably, but not necessarily, the lower surface 82 of the distal edge 46 of the frustoconical shoulder 44 is spaced from the first axial end 38 of the annular body a distance 70 that is equal to or less than, within acceptable manufacturing tolerances, a distance 72 between a lower edge 84 of a base of the gas lip 64 and the first axial end 38 of the annular body. The base of the gas lip 64 is the general location at which the gas lip 64 is attached to and extends from the stem seal portion 56, and is generally indicated by the dashed line 74.

[0020] By positioning the gas lip 64 at the approximate same axial location along the valve axis 30 as the distal edge 46 of the frustoconical shoulder 44, the distal edge 46 acts as a hinge or pivot to allow the stem seal portion 56 to rotate upward and away from the casing 32. More specifically, the frustoconical shoulder 44 allows the stem seal portion 56 of the elastomeric seal 34 to rotate radially outward away from the valve axis 30 and axially away from the first axial end 38 of the annular body portion 36 of the casing 32 in response to thermal expansion of the elastomeric seal 34. Allowing the stem seal portion 56 to rotate in this fashion maintains a substantially constant pressure and contact width between the gas lip 64 and the stem 26 of the exhaust valve 28, which maintains proper functionality of the gas lip 64 in high temperature and high pressure environments.

[0021] The detailed description and the drawings or figures are supportive and descriptive of the invention, but the scope of the invention is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed invention have been described in detail, various alternative designs and embodiments exist for practicing the invention defined in the appended claims.

Claims

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.degree. and 45.degree..

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.degree. and 45.degree..

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.