Patent Publication Number: US-6209504-B1

Title: Heavy-duty valve stem seal

Description:
FIELD OF THE INVENTION 
     The present invention relates to internal combustion engine valve seal retainers, and more particularly to a unitary annular retainer having an integral spring seat and close clearance for use with high power density heavy-duty engines. 
     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 commonly 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 along a free upper end of the valve stem toward the manifolds and valve heads by the force of gravity and may be encouraged by a pressure differential in the manifold versus crankcase pressure. 
     Annular valve stem seals are generally urged into contact with the outer surface of the valve stem and an upper portion of the valve guide by a valve stem seal retainer, and serve various purposes. First, valve stem seals minimize engine oil consumption by restricting oil entry into the manifold and the combustion chamber. Second, they help to minimize exhaust particulates that contribute to pollution. Third, they are helpful in minimizing guide wear, which is of particular importance in large diesel engines due to the nature of their operation. The valve stem, valve guide, and valve stem seals are annularly wrapped by a helical compression valve spring that serves to bias the valve into a closed position. The longitudinal ends of the valve spring are restrained by flanges on corresponding valve spring retainers and/or spring seats, thereby maintaining proper alignment and position of the valve and valve spring. 
     In the heavy-duty engine market a number of changes are being made to comply with recent and prospective emissions standards. As the construction of the engine changes, engine designers must nevertheless maintain a robust engine design with a sufficient level of dependability. One of the more prominent changes being implemented is the increase of the power rating of the engine in an effort to reduce the size of the engine. In particular, engine manufacturers are attempting to reduce the displacement of heavy-duty engines while still providing ample horsepower and torque for heavy-duty applications. As is well-known, engine displacement is calculated by multiplying cylinder bore area times the piston stroke length. In reducing the displacement of heavy-duty engines, manufacturers are reducing both the bore area and the stroke length while increasing the compression within the combustion chamber. Increasing the required amount of compression, in turn, places greater stress on the valve seal. Many of these engines are increasing their compression by up to 50-60 psig, which is a far greater pressure than many prior art valve seals can handle while being properly retained on a valve guide. For such cases, an integral valve seal with a metal retainer is normally recommended. 
     However, as the bore area of an engine is reduced, the area provided for valve assemblies above a combustion chamber is correspondingly reduced. The problem is especially significant in heavy-duty diesel engines because all valve assemblies are typically oriented perpendicular to the engine head. Additionally, a fuel injector occupies a large portion of the area above the cylinder bore. Thus, in high efficiency heavy-duty diesel engines having more than two valves (intake and exhaust valves) per cylinder, the area directly above the engine bore must be shared by a fuel injector and the valves. Since the size of the fuel injector is substantially fixed, a reduction in engine bore generally requires a reduction in the valve assembly diameter, including corresponding reductions in the diameter of valve stem seals, valve guides, and valve stem seal retainers. There is thus a need for a valve seal assembly capable of withstanding increased compression loads while providing a seal having close clearance and durability. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an integral valve stem seal retainer and spring seat for a reduced diameter valve seal assembly. The retainer includes lower and upper portions. An annular sealing member is bonded to the upper portion of the metal retainer and an annular flange extends radially outwardly of the lower portion of the retainer to engage at least one coil of a reduced diameter valve spring. The annular sealing member further includes upper and lower seals, wherein the upper seal engages an outer surface of a valve stem while the lower seal engages a top of a thin-wall valve guide. The lower portion of the retainer may include a plurality of radially inwardly extending tangs to positively engage an outer surface of the valve guide against axial and rotational movement. 
     The integral valve stem seal retainer and spring seat of the present invention allows a reduced diameter valve seal subassembly and provides a seal capable of withstanding high pressure while reducing wear in heavy-duty engines. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and inventive aspects of the present invention will become more apparent upon reading the following detailed description, claims, and drawings, of which the following is a brief description: 
     FIG. 1 is a side plan view of a cylinder bore of a heavy-duty high power density diesel engine. 
     FIG. 2 is a top plan view of a cylinder bore of a heavy-duty high power density diesel engine. 
     FIG. 3 is a perspective view of the valve assembly of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As noted above, reducing the displacement of heavy-duty engines causes a corresponding reduction in a cylinder bore area. In FIG. 1, a side plan view of a reduced area cylinder bore  10  is shown. FIG. 1 also shows in plan view a fuel injector  12 , and two valves  14 ,  16  corresponding respectively to intake and exhaust valves. As may be appreciated from FIG. 1, the valves  14 ,  16  extend generally perpendicular to the cross-sectional area of the cylinder bore  10 , and are not angled with respect to the combustion chamber. In comparison to a conventionally sized heavy-duty engine cylinder bore, shown in phantom as reference  18 , the reduced area bore  10  provides substantially less area above the bore  10  for placement of both the fuel injector  12  and the valves  14 ,  16 . 
     The space constraints associated with heavy-duty high power density engines are further illustrated with reference to FIG. 2, which shows the reduced diameter bore  10  from the top. In FIG. 2, the fuel injector  12  shares the area directly above the cylinder bore  10  with two pairs of valve assemblies  14 ,  16  (two intake and two exhaust valves). Again, because the valve assemblies  14 ,  16  and the fuel injector  12  extend generally perpendicular to the cross-sectional area of the cylinder bore  10 , the area allowed for each valve assembly  14 ,  16  is severely constrained. As may be appreciated, it is not practical to reduce the size of the fuel injector  12 . To enable the four valve assemblies  14 ,  16  and the fuel injector  12  to fit within the allocated space above each cylinder bore  10 , the corresponding cross-sectional area of the valve assemblies  14 ,  16  must be reduced. 
     One valve assembly, corresponding either to an intake valve  14  or an exhaust valve  16 , is shown in FIG.  3 . For purposes of the following description, the valve assembly in FIG. 3 will be referred to as an intake valve  14 , but it should be understood that the following description applies to exhaust valves as well. 
     In general, the components that most contribute to the cross-sectional area of the valve assembly  14  include a valve stem  20 , a valve guide  22 , and a valve spring  24 . In addition, the valve assembly further includes a valve stem seal  26  and a valve stem seal retainer  28 . When assembled, the valve stem  20  is seated in and surrounded by the annular valve guide  22 . In reducing the cross-sectional area of the valve assembly  14 , it is generally not possible to reduce the outer diameter of the valve stem  20  for structural reasons. Instead, reducing the outer diameter of both the valve guide  22  and the valve spring  24  achieves most of the cross-sectional area reduction. However, reducing the outer diameter of the valve guide  22  results in a relatively thin-walled valve guide. It is possible that the length of the valve guide  22  might be increased to provide effective support for the valve stem  20 . Unfortunately, increasing the length of the valve guide  22  results in more of the valve guide projecting above the engine head, which would require a deeper stamping operation to fabricate the valve stem seal retainer  28 . Even if the length of the valve guide  22  is not increased, however, it is relatively difficult for the valve stem seal  26  to remain in constant contact with the outer circumference  30  of the valve stem  20 , and also with the top portion  32  of the valve guide  22  while at the same time remaining free from interference from the valve spring  24 . As seen in FIG. 3, the valve stem seal  26  is supported by the valve stem seal retainer  28 . Generally, when the valve guide  22  projects upwardly a relatively large amount, the valve stem seal retainer  28  includes at least two pieces, including an upper portion for fixing the valve stem seal in place and a lower portion for preventing migration of the upper portion when the valve stem  20  reciprocates during engine operation. The lower portion may also include a flange for supporting a lower end of the valve spring  24 . 
     However, a multiple piece valve stem seal is inappropriate when cross-sectional area of the valve assembly is critical. Instead, according to the present invention, an annular integral valve stem seal retainer  28  is shown having upper and lower portions  34 ,  36  respectively. The upper portion  34  of the valve stem seal retainer  28  supports and is bonded to the elastomeric valve stem seal  26  along an outer circumference  38  thereof. The inner diameter D 1  of the retainer upper portion  34  is less than the inner diameter D 2  of the retainer lower portion  36  so that the valve stem seal  26  is firmly biased radially inwardly to make contact with the outer circumference  30  of the valve stem  20 . The lower portion  36  of the valve stem seal retainer  28  further includes a radially outwardly projecting annular flange  40  that acts to locate the retainer  28  against the upper surface  42  of the cylinder head  44 . An upper surface  46  of the flange  40  acts as a seat for a lower end of the valve spring  24 . By including the flange  40  with the valve stem seal retainer  28 , the valve seal may be fabricated and installed as a single subassembly comprising the valve stem seal  26 , the valve stem seal retainer  28 , and the spring  24 . The sealing subassembly is easier to install, especially given the space constraints above the cylinder bore as described above. 
     Likewise, because the retainer  28  is unitary in construction, the inner diameter D 2  of the retainer  28  lower portion  36  is less than if the retainer lower portion were a separate piece. Additionally, the retainer lower portion may include a plurality of radially inwardly projecting indentations or tangs  48  that act to secure the retainer to the outer surface  50  of the valve guide  22 . The tangs  48  also act to prevent the valve seal retainer  28  from lifting or rotating as the valve reciprocates during engine operation. 
     As noted above, an annular valve stem seal  26  is bonded to the outer circumference  30  of the valve stem  20  to provide a tight seal. In practice, the valve stem seal  26  includes an upper seal  52  and a lower seal  54 . The upper seal  52  includes a plurality of radially inwardly extending fingers  56  defining a number of recesses  58  in the face of the seal  26 . The fingers  56  contact the outer circumference  30  of the valve stem  20  to prevent ingress of excessive amounts of lubricant, while the recesses  58  provide a reservoir of lubricant to the valve stem as well as a location for excess oil to flow. The outer circumference  60  of the upper portion  52  of the seal  26  further includes a groove  62  for receiving an o-ring  64 , which prevents the seal upper portion  52  from deforming over the life of the seal. 
     The lower portion  54  of the valve stem seal  26  includes a frustoconical end  66  that extends axially from the upper seal to contact the top portion  32  of the valve guide. The outer diameter D 3  of the base  68  of the frustoconical end  66  is substantially equal to or slightly smaller than D 2 , and is therefore greater than the inner diameter D 1  of the retainer upper portion  34 , so that the valve stem seal  26  is tightly held against the outer circumference  30  of the valve stem  20 . By configuring the valve stem seal in this manner, the amount of elastomeric material needed to create effective sealing is reduced over conventional two-piece valve stem seal assemblies, thereby allowing for a seal having a reduced diameter. 
     The combination of the above-described features therefore enables construction of a valve seal assembly for use with reduced diameter valve guides  22 . The shape of the valve seal retainer allows an extremely small clearance T between the lower portion  36  of the retainer  28  and the outer circumference  38  of the valve guide  22 . At the same time, the flange  40  on the lower portion  36  provides an integral spring seat for use with a reduced diameter valve spring  24 . The valve seal subassembly of the present invention therefore provides a more compact assembly while not compromising sealability or durability of the seal. 
     Preferred embodiments of the present invention have been disclosed. A person of ordinary skill in the art would realize, however, that certain modifications would come within the teachings of this invention. Therefore, the following claims should be studied to determine the true scope and content of the invention.