Abstract:
A valve stem seal assembly includes two annular hydraulic seals separated by a generally flat support member, where the seals are axially positioned back to back on an upper free end of a valve stem. The seals and the washer are secured along a radially outer circumference by a retainer, a lower portion of which contacts an upper surface of a valve guide. The valve stem is slideably sealed by an inner annular surface of both hydraulic seals.

Description:
FIELD OF INVENTION 
     The present invention relates to a valve stem seal and more particularly to a seal that prevents oil flow down a valve stem toward a combustion chamber. 
     BACKGROUND OF THE INVENTION 
     In conventional overhead valve internal combustion engines, at least two valves reciprocate to provide intermittent communication between intake and exhaust manifolds and a combustion chamber. The valves include valve stems that are disposed in valve stem guides, supporting axial motion in an engine component such as an engine head. Lubrication is provided to upper portions of the valve stems by a spray of lubricating oil within a valve cover disposed over the engine head or by gravity flow from an associated rocker arm. Oil flows by the force of gravity and may be encouraged by a pressure differential in the manifold versus crankcase pressure along a free upper end of the valve stem toward the manifolds and valve heads. 
     Valve stem seals located between the valve stem and the valve guide serve various purposes. First, they minimize engine oil consumption by metering oil entry into the manifold and the combustion chamber. Second, they help to minimize exhaust particles that contribute to pollution. Third, they are helpful in minimizing guide wear. 
     However, increasingly stringent environmental protection regulation requires that vehicle emissions be reduced to produce lower pollution levels. Exhaust particles, as noted above, contribute to this pollution. Emission levels increase by allowing even minuscule amounts of oil past the valve stem seal and down the valve stem and into the combustion chamber. Current valve stem seals, however, are designed only to meter or limit oil flow and are incapable of completely eliminating oil flow down the valve stem and into a combustion chamber. 
     Accordingly, a valve stem seal is needed that prevents the flow of any oil down a valve stem past the valve guide and into the combustion chamber. 
     SUMMARY OF THE INVENTION 
     A valve stem seal assembly is provided to prevent oil flow down a valve stem into a combustion chamber that includes two annular hydraulic (zero-leak) seals separated by a generally flat support member, where the seals are axially positioned back to back on an upper free end of a valve stem. The seals and the washer are secured along a radially outer circumference by a retainer, a portion of which contacts an upper surface of a valve guide. The valve stem is slideably sealed by an inner annular surface of both seals. 
     Preferably, each hydraulic seal includes a generally U- or V-shaped radial cross-section formed by inner and outer legs separated by a radial transverse portion. The seal may include a support such as a spring in the radial cross-section of each seal. The spring provides an inwardly radial force to hold the seal in place against the valve stem while giving the seal assembly a longer life-span during reciprocation of the valve stem. When assembled, the transverse portions of each respective hydraulic seal are placed in adjacent relationship and are separated by the support member, such that the inner legs of each respective seal define upper and lower sealing lips that contact the valve stem, and such that the outer legs of each respective seal contact the retainer. The support member may be a rigid precision washer. 
     The upper sealing lip acts to prevent the flow of all overhead oil down the valve stem. In particular, the retainer provides sufficient radial pressure on the upper seal to cause the upper sealing lip to completely seal the valve stem against downward oil flow. Additionally, during reciprocating action of the valve, the upper sealing lip scrapes oil off the valve stem, collecting the oil within a U- or V-shaped reservoir portion of the upper seal such that the oil within the reservoir exerts a further radially inward pressure on the upper seal. Similarly, the lower sealing lip prevents pressure from the exhaust and intake manifolds from upsetting the sealing action of the upper seal. The upper and lower sealing lips thus combine to completely eliminate an oil leak path into the combustion chamber, thereby reducing harmful emissions. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     A number of features and advantages of the present invention will become apparent from the detailed description of the invention that follows and from the accompanying drawings, wherein: 
     FIG. 1 is a cross sectional view of a valve stem seal according to the present invention. 
     FIG. 2 is an enlarged detailed view of Circle A of FIG. 1 showing the positioning of the valve stem seal of the present invention. 
     FIG. 3 is an enlarged detailed view of Code A of FIG. 1 showing a second embodiment of the valve stem seal assembly of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A valve assembly  10  for use in an internal combustion engine is shown in FIG. 1 that includes a valve stem  20 , a valve stem guide  22 , and a valve stem seal  24 . During operation of the engine, valve stem  20  is caused to reciprocate by an associated rocker arm assembly (not shown) or similar device. During reciprocating operation, an upper portion  26  of valve stem  20  is exposed to a spray or bath of lubricating oil. A lower portion  28  of valve stem  20  is supported by guide  22  as it extends through an engine head  29 . Lower portion  28  is further connected to a valve head (not shown) that extends into a portion of a combustion chamber (not shown) for introducing or exhausting gasses. 
     Valve stem seal  24  is placed around the valve stem upper portion  26  to seal against oil flowing downwardly in the direction of arrow  30  along the outer surface  32  of the valve stem. Since even a minute amount of oil entering the combustion chamber increases harmful emissions, valve stem seal  24  is designed to prevent any oil from flowing downwardly along surface  32  through guide  22 . 
     Seal assembly  34  is shown in greater detail in FIG.  2 . The seal assembly includes upper and lower hydraulic seals  40 ,  42  separated by a spacer member  44  and held in place by retainer  46 . Upper seal  40  includes inner and outer legs  48 ,  50  separated by a radial transverse portion  52  to form a U- or V-shaped radial cross-section. Similarly, lower seal  42  includes inner and outer legs  54 ,  56  separated by a radial transverse portion  58  to form an inverted U- or V-shaped radial cross-section. If desired, seals  40 ,  42  may be formed of different materials. However, seals  40 ,  42  are preferably identical hydraulic seals oriented such that the respective radial transverse portions  52 ,  58  are aligned adjacent each other and rest upon opposite sides of spacer member  44 . Spacer member  44  is preferably rigid, and may be a precision annular washer having an outer diameter slightly smaller than the outer diameter of each seal  40 ,  42 . 
     The seals and the spacer member are held in place and the seals are compressed against valve stem surface  32  (see FIG. 1) by retainer  46 . Retainer  46  also locates the valve seal assembly  34  in place along the valve stem. A lower portion  60  of retainer  46  engages an upper part of valve guide  22  (see FIG.  1 ), while an upper radially inwardly extending retainer upper portion  62  prevents longitudinal movement of the seals. Additionally, an annular inner surface  64  of retainer  46  contacts the outer circumference of seals  40 ,  42  and of member  44 . Since the outer diameter of member  44  is slightly smaller than the outer diameter of the seals, the seals are compressed radially inwardly by retainer  46  towards the valve stem. With respect to upper seal  40 , upper sealing lip  66  contacts surface  32  and acts to scrape oil off of the valve stem during reciprocation. With respect to lower seal  42 , lower sealing lip  68  prevents pressure from the combustion chamber from upsetting the sealing action of upper sealing lip  66 . 
     Seal assembly  34  is designed so that the sealing ability of the assembly improves during valve reciprocation. As stem  22  reciprocates, upper sealing lip  66  scrapes oil from the valve outer surface. As oil is scraped, it is collected in an oil reservoir  70  formed in the concave portion of upper seal  40 . The constant extraction of oil from valve stem  22  causes the reservoir to fill. At the same time, retainer upper portion  62  covers at least a portion of the cross sectional area of the upper seal  40 , acting as an obstruction against oil flow out of the reservoir. The U- or V-shape of upper seal  40  acts to convert the oil flow from directly longitudinal flow to a radial flow, and the retainer upper portion likewise converts flow from longitudinally upward to primarily radially inward, thereby increasing the radial pressure on the upper sealing lip  66 . However, since the retainer upper portion  62  does not completely cover upper seal  40 , a secondary flow of oil is allowed to escape from reservoir  70  through exposed cross sectional area of the upper seal. Thus, as more oil is scraped into reservoir  70 , the radial pressure on the seal increases, thereby increasing the effectiveness of upper sealing lip  66 . 
     Lower seal  42  serves to prevent pressure from the exhaust and intake manifolds from upsetting the sealing action of the upper seal. Pressure from the manifolds is collected in concave portion  72  of the lower seal and acts to exert radial pressure on the lower sealing lip  68  in the same way that oil in reservoir  70  exerts radial pressure on upper sealing lip  66 . At the same time, the support member  44  prevents twisting of either the upper or lower seal, while preventing radial crushing of the retainer and seals. To allow free reciprocation of valve stem  20 , the radially inner diameter of support member  44  is preferably greater than the outer diameter of the valve stem. However, radially inner surface  74  of member  44  may also include a low friction coating or the like to promote easy sliding of the valve stem past the support member. 
     A preferred embodiment of seal assembly  134  is shown in FIG.  3 . The seal assembly includes upper and lower hydraulic seals  140 ,  142  separated by a spacer member  144  and held in place by retainer  146 . Spring reinforcements  141 ,  143  may be positioned in the radial cross-section of upper and lower hydraulic seals  140 ,  142 . Preferably, springs  141 ,  143  include a U- or V-shaped radial cross section such that legs  155 ,  157  of springs  141 ,  143  exert force in a radial outward and radial inward direction, respectively. However, springs  141 ,  143  may be of any type that exert at least a radially inward force. Once springs  141 ,  143  are positioned in the cross-section of seals  140 ,  142 , the springs  141 ,  143  will force seals  140 ,  142  to conform to the shape of springs  141 ,  143 . The sealing action of seals  140 ,  142  with the inclusion of preferred U- or V-shaped springs  141 ,  143  are selectively focused on inner and outer legs  148 ,  150  which are separated by a radial transverse portion  152  to form a U- or V-shaped radial cross-section. Springs  141  and  143  both provide a superior sealing action of upper and lower hydraulic seals  140 ,  142  by exerting a greater inward and outward radial force from legs  148 ,  150  upon surface  132  and retainer  146 . 
     Instead of metering the oil flow past the valve guide, the valve stem seal assembly described above is designed to completely eliminate the oil leak path along the valve stem. Since oil flowing past the valve guide into the combustion chamber contributes significantly to harmful emissions, eliminating the oil flow entirely greatly reduces emissions while providing adequate sealing between the valve stem and the intake and exhaust manifolds. Although certain preferred embodiments of the present invention have been described, the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention. A person of ordinary skill in the art will realize that certain modifications will come within the teachings of this invention and that such modifications are within its spirit and the scope as defined by the claims.