Patent Publication Number: US-6659469-B1

Title: Molded rubber jacket with fabric reinforcement for valve stem seal

Description:
CROSS-NOTING TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 09/858,618, filed May 16, 2001 now U.S. Pat. No. 6,527,275, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to valve stem seal assemblies for use in internal combustion engines, and more particularly to the design and construction of molded elastomeric seal components employed in such seal assemblies. 
     2. Description of the Related Art 
     Those skilled in the art will appreciate the manner in which intake and exhaust valves are employed in cylinder heads of internal combustion engines. Such valves, supported for reciprocal motion within valve guides, include integral elongated stems extending away from the engine cylinder heads, the ends of the stems typically interacting with rotating overhead cams for cyclic or repeated opening and closure of the valves against the force of valve return springs during the combustion cycle. In order to permit unobstructed reciprocal movement of the stem in the guide, some mechanical clearance must obviously exist between the valve guide and the moving stem. In fact, a plurality of such valve stems move reciprocally in valve guides, to and from the cylinder head, each within its individual guide. So-called valve stem seal assemblies are used to seal against leakage of oil through a mechanical clearance path between each annular engine valve guide and its associated valve stem. 
     As is well known, the intake port of a combustion chamber is opened and closed by the reciprocating motion of at least one intake valve, which in turn is driven by the rotary motion of a cam, the latter being affixed to and rotatable with an engine camshaft. The intake valve permits fuel mixed with air to flow into the combustion chamber. In addition, an internal combustion engine has at least one exhaust valve and associated exhaust port for releasing expended combustion gases to the atmosphere. Typically, intake and exhaust valves are of similar construction and both include stems integrally affixed to the valves. 
     In some engines, a unitary elastomeric valve stem seal component is fitted over or atop each valve guide, wherein the seal component is frictionally mounted directly to the guide. In other cases the seal is encased within or otherwise secured to a rigid, typically metal, seal retainer to form an assembly, as required in some applications to assure proper securement of the seal to the guide. Those skilled in the art will appreciate that pluralities of such elastomeric valve stem seal components are employed in typical engines. In the case of a V-8 engine, a total of at least 16 valve stem seals are employed, one for each intake and one for each exhaust at each cylinder, depending on actual number of valves employed per cylinder in a particular engine. 
     Traditional elastomeric seal components have been fabricated using techniques that address only the chemical compositions of various elastomeric materials employed. Thus, even in environments wherein tougher elastomeric materials may be required, only the material compositions have been modified to enhance strength of materials as desired. In many cases, this approach has been fraught with significant technical complexity, and has yielded minimal results. 
     In addition, traditional manufacture of such seals has been only on a unitary batch basis, or via one batch at a time. Thus, although much progress has been achieved in the art of valve stem seal design and construction, cost-effective techniques for enhancement of strength of materials, along with streamlined manufacturing techniques remain areas in need of additional improvement. 
     SUMMARY OF THE INVENTION 
     The improved valve stem seal component of the present invention overcomes the traditional compositional limitations of prior art elastomeric seals with respect to enhancement of strength of materials, and also significantly streamlines valve stem seal component manufacturing, both in a cost-effective assembly line process. 
     The present invention provides an elastomeric seal component adapted for installation directly atop of a valve guide of an internal combustion engine. A plurality of such seal components is contemplated for use in an engine, each component designed for insertion over each engine valve guide of a given engine. Each component is adapted for continuously and sealingly engaging an associated reciprocally movable valve stem. The seal component body incorporates an interior circumferential aperture containing at least one radially inwardly directed, resilient, sealing lip adapted to engage the stem to minimize escape of oil lubricant from the engine along a path between the valve guide and the reciprocally movable valve stem. 
     The unique seal component incorporates fabric reinforcement within the annular jacket body of the seal body. In one preferred form, the fabric is positioned intermediately between two layers of the seal body; i.e. between an inner layer and an outer layer. 
     Finally, two manufacturing methods are presented for manufacture of the seal component. A first provides for extrusion of a tube having the fabric reinforcement layer already provided between inner and outer layers. A cutting die incorporates a push ring adapted to move the component along a staged molding assembly process. A series of threaded core pins are utilized for conveyance of the component in the fabrication process from one stage to the next. The preferred method consists of extruding a rubber tube and cover over a series of threaded core pins, the tube including a fabric reinforcement material positioned intermediate the tube layers; cutting a portion of the rubber tube to a predetermined length; molding the predetermined length of the tube to produce an annular valve stem seal component; curing the molded component; and removing the component from the mold. 
     An alternate method, called a transfer mold approach, provides molding an inner tube over a threaded core pin; applying a spiral knit reinforcement fabric to the exterior of the inner tube; molding a cover to the tube so as to directly overlie the reinforcement fabric to thus form a fabric reinforced valve stem seal; curing the seal component; and then removing the seal component from the core pin. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a cross-sectional view of one preferred embodiment of the valve stem seal component of the present invention. 
     FIG. 2 is a cross-sectional view of the same preferred embodiment of the valve stem seal component, showing same to be installed over a valve guide in an internal combustion engine. 
     FIG. 3 is a cross-sectional view of an extrusion process employed in the manufacture of the valve stem seal component of the present invention. 
     FIG. 4 is a cross-sectional view of an alternate, transfer mold, process for manufacturing the valve stem seal component of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to FIGS. 1 and 2, a valve stem seal component  10  is formed of a resilient material, having an exterior annular body surface  12  and an interior circumferentially extending body surface  14 . The component  10  includes an upper jacket body portion  16  and a lower jacket body portion  18 , the upper body portion containing a circumferentially extending interior sealing lip  20 . The lip  20  is adapted to sealingly engage an elongate valve stem  22 . The valve stem  22  extends upwardly from a valve  24  (shown broken away from stem  22 ) adapted to close against a valve seat (not shown) in the top of a combustion chamber (not shown). The stem  22  is supported for reciprocal movement within an annular valve guide  26 . The guide  26  is fixedly secured in, and extends longitudinally (or upwardly, as shown) through, an aperture  29  of a cylinder head deck  30 . 
     For sealing engagement of the reciprocally moving valve stem  22 , the interior body surface  14  of the seal component  10  is frictionally supported directly to the exterior circumferential surface  28  of the valve guide  26 . The circumferentially extending sealing lip  20  is adapted to engage the exterior circumferential surface of the stem  22  for limiting and or otherwise controlling movement of crankcase oil along a mechanical clearance path  31  between the stem  22  and the valve guide  26 , for undesirable escape of oil into the combustion chamber, as will be appreciated by those skilled in the art. In this particular embodiment, the seal component  10  is frictionally and circumferentially supported directly on the valve guide  26 . However, in other embodiments, depending in part on operating conditions, a seal retainer (not shown) can be employed to secure the elastomeric seal component  10  onto the guide  26 . In most such cases, the retainer will have a shape adapted to matingly register with the exterior annular body surface  12  of the seal component  10 . Finally, to enhance sealing effectiveness, a garter spring  21  encircles the exterior upper body portion  16 , radially outwardly of the sealing lip  20 , to impart a radial compression force against the lip  20 , and ultimately against the reciprocally moving valve stem  22 . 
     Referring now specifically to FIG. 1, the construction of the seal component  10  of this invention incorporates an inner elastomeric tube  32  and an outer elastomeric cover  34  molded together. Intermediately positioned between tube and cover, however, is a fabric reinforcement  40  for imparting strength, robustness, and enhanced integrity for avoiding tears or other potential deterioration of the seal walls. As such, a skeleton or frame is encapsulated within the elastomeric seal component  10 , which may be manufactured via either extrusion or transfer molding processes as described below. In a preferred form, the fabric reinforcement  40  may be applied in a knit form using a nylon or cotton material, preferably arranged in a spiral pattern for enhanced strength. A geometric repetitive pattern such as a diamond-shaped configuration (not shown) is one example of such a preferred design. 
     Referring now to FIG. 3, a preferred combination method of extruding and molding the seal component  10  is demonstrated in stages represented from left to right as A, B, C, and D. A combination inner elastomeric tube  32  and outer elastomeric cover  34  with the fabric reinforcement  40  already contained therebetween is installed over a threaded core pin  50  as shown at stage A. The threaded core pin  50  is in turn threaded to a longitudinal series of threaded core pins so as to accommodate a continuous process involving stages A through D. At stage B, a predetermined length of the combination tube  32  and elastomeric cover  34  enters a tube mold  54  whereupon a predetermined length is cut by the blade  48  of a cutting die/push ring  52 . Within the tube mold  54 , the valve stem seal component  10  is shaped via a molding process. Thereafter, the component  10  is cured at stage C. Finally, at stage D, the push ring  52  advances, as indicated by the arrows, to push the completed seal component  10  off of its core pin  50 . At this point, the core pin  50  at stage D is unthreaded from trailing core pin  50  at stage C, and is re-threaded at the start of the process at stage A. 
     Referring now to FIG. 4, an alternate so-called transfer mold process is depicted in stages A′, B′, C′, D′, and E. At stage A′, elastomeric material is transferred into a tube transfer mold  54 ′ through a set of mold sprues  44  about a first of a series of threaded core pins  50 ′. At stage A′ the inner elastomeric tube  32  is first formed as shown. A push ring  52 ′ thereafter advances the tube  32  to stage B′. At stage B′ a spiral knit reinforcement fabric  42  is applied to the tube  32 , with for example a needle spiral knitter (not shown). Next the push ring  52 ′ advances the product-in-process to stage C′ wherein the outer cover  34  is molded into place within a second tube transfer mold  54 ″, the elastomeric material entering through a second set of sprues  46  as shown. The push ring  52 ′ next advances the product-in-process to stage D′ wherein curing of the elastomeric material takes place. Finally, at stage E, the push ring  52 ′ advances, in direction of the arrows, to remove the finished seal component  10  from its threaded core pin  50 ′. 
     It is to be understood that the above description is intended to be illustrative, and not limiting. Many embodiments will be apparent to those of skill in the art upon reading the above description. The scope of the invention should be determined, however, not with reference to the above description, but with reference to the appended claims and the full scope of equivalents to which the claims are entitled by law.