Abstract:
A baffle for use in an interior of a cam cover and a method of making the baffle are disclosed. The baffle includes a structural layer, which is made of metal, and an isolation layer that is made of a resilient foam. The isolation layer is disposed on a surface of the structural layer in a pattern that leaves uncovered a portion of the surface of the structural layer. When the baffle is installed in the cam cover, the isolation layer provides an interface between the structural layer and the cam cover, which isolates the baffle from vibrations in the cam cover. Since the isolation layer is applied only where it is needed, the disclosed baffle and process use less material.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to baffles employed in cam covers of motor vehicle engines, and more particularly, to methods and materials for isolating the baffles from vibrations transmitted through the cam covers. 
     2. Discussion 
     Cam cover baffles used in motor vehicle engines aid in the removal of oil mist entrained in crankcase gases and are designed to optimize crankcase airflow through the cam (valve) cover. Conventional cam cover baffles are typically formed of a thin, single layer of stamped metal, such as steel. One problem with such baffle designs is that engine vibrations may cause the metal layer to resonate, resulting in undesirable noise generation. Designers have employed several techniques for resolving noise and vibration issues, including applying energy dissipating coatings on the metal layer. 
     Although baffle designs employing energy dissipating coatings have met with some success, the use of coatings creates other problems. For example, coatings add mass, and increase the material costs and labor associated with manufacturing the baffle. Additionally, it is often difficult to accurately control the thickness of the coating, which may result in sealing difficulties between the baffle and the cam cover and may lead to improper control of PCV emissions. Furthermore, portions of the coating may detach from the baffle during engine operation, which may contaminate the crankcase. 
     The present invention overcomes, or at least helps reduce the effects of one or more of the problems set forth above. 
     SUMMARY OF THE INVENTION 
     The present invention provides a baffle that is adapted for use in an interior of a cam cover, which addresses many of the problems described above. The baffle includes a base layer, which is made of metal, and an isolation layer that is comprised of a resilient foam. The isolation layer is disposed on a surface of the base layer in a pattern that leaves uncovered a portion of the surface of the base layer. When the baffle is installed in the cam cover, the isolation layer provides an interface between the base layer and the cam cover, thereby isolating the baffle from vibrations in the cam cover. 
     Another aspect of the invention provides a baffle that is adapted for use in an interior of a cam cover, which includes first and second structural layers, and a viscoelastic adhesive layer that is interposed between the two structural layers. The baffle also includes an isolation layer that is comprised of a resilient foam, which is disposed on a surface of the first structural layer in a pattern that leaves uncovered a portion of the surface of the first structural layer. The isolation layer provides an interface between the first structural layer and the cam cover when the baffle is installed in the interior of the cam cover. 
     Still another aspect of the invention provides a method of making a baffle for a cam cover. The method comprises providing a structural layer and applying an isolation layer on a surface of the structural layer in a pattern that leaves uncovered a portion of the surface of the structural layer. The isolation layer is comprised of a resilient foam, which dampens vibrations transmitted through the cam cover. In addition to providing improved vibration isolation, the inventive baffle and method use less materials and labor than conventional baffle manufacturing processes since the isolation layer is applied only where it is needed. Because the isolation layer does not completely cover the surface of the structural layer, and for the most part is sandwiched between the structural layer and the cam cover, there is less chance that the foamed material will detach from the baffle. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of an interior of a cam cover adapted to receive a baffle. 
     FIG. 2 is a plan view of one embodiment of a baffle for use in the cam cover of FIG.  1 . 
     FIG. 3 is an enlarged cross-sectional side view of the baffle as viewed along section line  3 — 3  of FIG.  2 . 
     FIG. 4 is a plan view of the cam cover of FIG. 1, showing the baffle of FIG. 2 installed in the interior of the cam cover. 
     FIG. 5 is an end view of the cam cover and baffle, as viewed through section line  5 — 5  of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a motor vehicle engine cam (valve) cover  10  is adapted to be securely attached to a cylinder head (not shown). Such cam covers have been traditionally made of stamped steel, but in recent years have also been made of molded plastic, cast aluminum, or cast magnesium materials. The cam cover  10  of FIG. 1 is formed of cast magnesium, and has a longitudinal dimension that extends along an axis a-a, as shown. 
     The cam cover  10  includes a plurality of bosses  12  for attachment of the cover  10  to the cylinder head of the engine. The bosses  12  include apertures  14 , which permit passage of bolts that are used to secure the cam cover  10  to the cylinder head. The cam cover  10  comprises an interior  16  that includes a positive crankcase ventilation (PCV) aperture  18 , which allows crankcase gases to vent through the cam cover  10  during engine operation. 
     The cover  10  incorporates other apertures  20 , which may accommodate additional engine hardware, including cam phasers and similar electronic devices. The cam cover  10  also includes ribs  22  that extend laterally (i.e. transversely to the axis a-a) across sections of the interior  16  of the cam cover  10 . In addition to providing structural support, and as discussed below, the ribs  22  create turbulence within a channel defined by a baffle  24  (FIG. 2) and the interior  16  of the cover  10 . 
     Referring to FIG.  1  and to FIG. 2, the baffle  24  includes a plurality of attachment apertures  26  that mate with a series of posts  28  when the baffle  24  is installed in the interior  16  of the cam cover  10 . The posts  28 , which are typically made of metal, are integrally affixed to the interior  16  of the cam cover  10 , and are adapted to be heat staked—i.e., flattened against the baffle  24 —in order to secure the baffle  24  to the cam cover  10 . Other embodiments may use rivets, screws, etc. to attach the baffle  24  to the interior  16  of the cam cover  10 . 
     As can be seen in FIG. 3, which is a cross-sectional view of the baffle  24  through reference line  3 — 3  of FIG. 2, the baffle  24  comprises four distinct layers. The baffle  24  includes a second structural layer  32  and a base structural layer  34  that are affixed to one another (i.e. constrained) using a viscoelastic layer  36 , which is interposed between the metal layers  32 ,  34 . An isolation layer  38  is selectively applied to the base structural layer  34 , and is advantageously made of a resilient foamed material as described below. Other embodiments may include baffles comprised of more or less than four layers, but would normally include at least the base structural layer  34  and the isolation layer  38 . 
     Suitable materials for the structural layers  32 ,  34  include, without limitation, stamped metal plates, heat resistant plastics, and high temperature thermosetting polymers, etc. Particularly useful structural layers  32 ,  34  include those made of steel. The thickness of the structural layers  32 ,  34  is not critical, but typically lies within a range of about 0.2 mm to about 0.6 mm. 
     The viscoelastic adhesive layer  36  helps convert vibrational energy into heat, thereby dampening resonant vibrations that may generate noise. The viscoelastic layer  36  should be resistant to engine oil and should provide adequate adhesion between the structural layers  32 ,  34  at temperatures en countered in engines (e.g., up to about 150° C.). Useful viscoelastic adhesives may include, but are not limited to vulcanized or cross-linked elastomeric polymers. Such materials include natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, chloroprene rubber, butadiene acrylonitrile rubber, butyl rubber, ethylene propylene rubber (EPM, EPDM), acrylic rubber, halogenated butyl rubber, olefin-based rubber, urethane-based rubber (AU, EU), hydrin rubber (CO, ECO, GCO, EGCO), polysulfide-based rubber, silicone-based rubber, fluorine-based rubber (FKM, FZ), polyethylene chloride rubber, and blends of two or more of these elastomers. 
     The components or precursors of the viscoelastic adhesive layer  36  (e.g., base polymer and cross-linking agent) are blended together and then applied to the one or both of the structural layers  32 ,  34  using any conventional technique, such as roller coating, dipping, brushing, spraying, screen printing, and the like. Following application, the viscoelastic layer  36  is partially cured or B-staged so that it remains tacky. The two structural layers  32 ,  34  are then bonded together under heat and pressure (C-staged). 
     The precursors of the viscoelastic adhesive layer  36  may be cured or cross-linked using any known mechanism, including convection or radiation heating, or exposure to high-energy radiation, including electron beams or ultraviolet (UV) radiation. Useful UV curable adhesives typically comprise mixtures of multifunctional acrylate monomers and oligomers, photoinitiators, and surfactants. In addition to the base polymer or polymers and cross-linking agent, the viscoelastic adhesive layer  36  may include particulate fillers (e.g., carbon black, silica, etc.), antioxidants, plasticizers, curing co-agents, activators and catalysts, pot life extenders, and the like. The thickness of the viscoelastic adhesive layer  36  is not critical, but is usually about 0.15 mm or less. 
     Referring to FIG.  1  through FIG. 3, the isolation layer  38  does not completely cover the surface  40  of the base structural layer  34 , but is disposed on the surface  40  in a pattern that leaves uncovered (exposed) a portion of the surface  40 . In the embodiment shown in FIG. 2, the isolation layer  38  is present only on regions of the baffle  24  that will contact the cam cover  10 . In other embodiments, the isolation layer  38  may cover more of the surface  40  of the base structural layer  34 . 
     Selective application of the isolation layer  38  minimizes material costs and mass of the baffle  24 , while providing an interface (i.e., vibration isolation) between the baffle  24  and the cam cover  10 . For the baffle  24  shown in FIG. 2, the isolation layer  38  covers regions or strips located adjacent to first  42  and second  44  longitudinal edges of the baffle  24  and around the attachment apertures  26 . When installed in the interior  16  of the cam cover  10 , the isolation layer  38  adjacent to the first  42  and second  44  longitudinal edges of the baffle  24  contact and seal, respectively, undulating  46  and relatively straight  48  ridges that extend along axis a-a of the cam cover  10 . Similarly, the isolation layer  38  located in regions around the attachment apertures  26  contacts and seals shoulders  50  circumscribing the posts  28 . 
     As noted above, the isolation layer  38  comprises a resilient foamed material (e.g., closed cell material). Precursors or components of the foamed material include one or more cross-linkable polymers, a curing agent, and a blowing agent that generates gas when activated (e.g., heated). The isolation layer  38  may also include particulate fillers, antioxidants, plasticizers, curing co-agents, activators and catalysts, pot life extenders, and the like. The cross-linkable polymer may be one or more of the elastomeric materials used in the viscoelastic adhesive layer  36  described above. Like the viscoelastic adhesive layer  36 , following cure the foamed material should be resistant to engine oil and should adhere to the requisite structural layer  34  at temperatures encountered in engines. Typically, the foamed material will exhibit at least about fifty percent compression at low stress levels (e.g., about 100 psi). 
     Particularly useful cross-linkable polymers include silicone rubber (e.g., polydimethylsiloxane), acrylonitrile butadiene rubber, and mixtures of acrylonitrile butadiene rubber and epoxy resin, which may be cross-linked using conventional curing agents. Any blowing agent may be used as long as it is compatible with the cross-linkable polymer. Suitable blowing agents include microspheres that expand upon heating and are available under the trade name EXPANCEL from EXPANCEL Inc. Other useful blowing agents include activated azodicarbonamide materials, which are available under the trade name CELOGEN from UNIROYAL CHEMICAL. 
     Prior to application, the isolation layer  38  precursors are blended together and applied to the surface  40  of the metal layer  34  using screen printing. Depending on the viscosity of the isolation layer  32  components, the screen mesh size may range from about  120  mesh to about forty mesh, though in many cases the mesh size may range from about sixty mesh to about forty mesh. Prior to foaming and curing, the isolation layer  38  may have a thickness ranging from about 0.2 mm to about 1 mm and between about 0.3 mm and about 1.5 mm when expanded (foamed). In many cases the foamed thickness may lie in a range from about 0.3 mm to about 0.5 mm. 
     Referring again to FIG.  1  and to FIG. 2, The baffle  24  includes a plurality of spaced-apart notches  52 , which help locate the baffle  24  in the interior  16  of the cam cover  10 . Each of the notches  52  is configured to mate with or clear one of the transverse ribs  22  located in the interior  16  of the cam cover  10 . The baffle  24  also includes lateral edges  54 ,  56  that extend between the first  42  and second  44  longitudinal edges of the baffle  24  in a direction transverse to axis a-a. The lateral edges  54 ,  56  of the baffle  24  do not abut the cam cover  10 , but provide a clearance between the interior  16  of the cam cover  10  and the baffle  24 . 
     This can be seen in FIG.  4  and FIG. 5, which show, respectively, a plan view of the baffle  24  installed in the interior  16  of the cam cover  10 , and an end view of the cam cover  10  and baffle  24 , viewed through section line  5 — 5  of FIG.  4 . The baffle  24  is mounted on the cam cover  10  with the surface  40  of the base structural layer  34  and the isolation layer  38  facing the interior  16  of the cam cover  10 . The ends  58  of the posts  28  have been heat staked against an outer surface  60  of the secondary structural layer  32  in order to secure the baffle  24  to the cam cover  10 . 
     The clearances  62 ,  64  between the cam cover  10  and the lateral edges  54 ,  56  of the baffle  24  permit crankcase air to enter a channel  66 , which is defined by the inward-facing surface  40  of the baffle  24  and the interior  16  of the cam cover  10 . The crankcase air flows through the channel  66  and exits the cam cover  10  through the PVC aperture  18 . The transverse ribs  22  create turbulence in the crankcase air as it flows through the channel  66 . As a result of the turbulence, oil mist entrained in the crankcase airflow will tend to settle out of the gas stream, coalescing as droplets on the inward-facing surface  40  of the baffle  24 , on the cam cover  10  ribs  22 , etc. A series of oil drain holes  68  permit the oil droplets to escape from the channel  66 . 
     EXAMPLE 
     A baffle was made by screen printing a foamed isolation layer on a steel plate. The components of the isolation layer included a silicone rubber, which was obtained from WACKER SILICONES of Adrian, Mich. under the designation ER93018. The silicone rubber included a major portion of polydimethylsiloxane, a minor portion (about one wt. % to about five wt. %) of trimethoxy[3-(oxiranylmethoxy)propyl]-silane, an organoplatinum curing catalyst, a cure inhibitor to improve pot life, and expandable microspheres (blowing agent). The silicone rubber was screen printed on the steel plate to a nominal thickness of 0.25 mm using a THIEME Model No. 1020 screen printer and a 60 mesh screen. The isolation layer was cured in a convection oven for ten minutes at about 149° C. The resulting foamed isolation layer had a thickness of about 0.44 mm and exhibited 55.7% compression under 100 psi stress. 
     It is to be understood that the above description and Example are intended to be illustrative and not limiting. Many embodiments will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of the invention should be determined, not with reference to the above description, but with reference to the appended claims with the full scope of equivalents to which the claims are entitled.