Patent Abstract:
A cover assembly for an internal combustion engine application and method of construction therefore provides one construction for a valve cover assembly, and another construction for an end cover assembly for a crankcase. The cover assemblies include at least one rigid metal carrier having a plurality of bolt openings and a plurality of load limiters located about said openings. A material is overmolded on the carrier and about the load limiters, with the material forming an exposed sealing surface for direct engagement with a seal gasket.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/772,293, filed Feb. 10, 2006, and U.S. Provisional Application Ser. No. 60/772,294, filed Feb. 10, 2006, which are both incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to internal combustion engines, and more particularly plastic covers for internal combustion engine applications. 
     2. Related Art 
     Covers for internal combustion engine applications, such as valve covers and rear engine covers for automotive and other internal combustion engine applications typically are made of die cast metal, metal stampings or molded thick-walled thermoset or thermoplastics materials. The covers typically have an elongated trough-like structure and have a perimeter flange formed with a series of spaced bolt holes that enable the cover to be bolted onto an associated cylinder head or rear portion of the engine. Use of the above materials (including the thick-walled plastics materials) is due in large part to the requirement that the cover have sufficient structural stiffness and stability under changing operational conditions (e.g., temperature, vibration, loading) to support and maintain a good seal with a seal gasket that is typically placed between the valve cover and the cylinder head to avoid oil leakage between the cover and head. 
     The all-metal valve covers are common, but are costly and heavy. The thick-walled all-plastic valve covers can be less costly and can contribute to a reduction in weight, but often the structural and dimensional stability requirements call for such large wall thicknesses that the benefits offered by the plastics material are offset by the bulkiness of the product and space requirements taken up by the added wall thickness. The thermoset materials are relatively stiffer than the thermoplastics materials, but they are more costly. Another issue with all-plastic covers is the need for added fasteners as compared to the all-metal covers in order to adequately prevent leakage. As such, the span between adjacent bolt holes is decreased and the number of fasteners is increased compared to metal valve covers, thus, adding to the cost and weight of the valve cover assembly. To date, a commercially suitable plastic valve cover that takes advantage of the benefits of what plastics have to offer has not been fully exploited, due in large part to the structural and dimensional limitations of the available plastics materials. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes or greatly minimizes the foregoing limitations of the known prior art valve cover assemblies. 
     A cover assembly for a valve cover or rear engine cover according to a presently preferred embodiment of the invention comprises a rigid metal carrier or frame structure that is overmolded with plastics material. 
     According to one feature of a valve cover constructed in accordance with the invention, a metal carrier of the valve cover includes a plurality of arch-shaped truss portions that are spaced laterally from one another along the length of the valve cover assembly, at least some of which are spaced from opposite longitudinal ends of the assembly. 
     According to another feature of a cover constructed in accordance with the invention, a metal carrier of the cover assembly includes flange reinforcement portions that extend along a perimeter of the cover assembly. The flange reinforcement portions are formed with a plurality of bolt hole openings that are spaced from one another. 
     According to still another feature of a cover constructed in accordance with the invention, a plastics material is overmolded about an underside mounting surface of the flange reinforcement portions to provide a sealing surface of the assembly for direct engagement with a seal gasket. 
     According to yet a further feature of a cover constructed in accordance with the invention, the plastics material is preferably a thermoplastics material and is of a relatively thin-walled construction. By thin-walled, it is meant that the wall thickness of the plastics material would be insufficient in itself (i.e., without the metal carrier) to be suitable for a valve cover for the intended application. 
     According to yet another feature of a cover constructed in accordance with the invention, the metal carrier is fabricated of stamped metal material 
     Covers constructed in accordance with the invention have the advantage of having thin-walls with structural and dimensional integrity normally associated with all-metal covers. 
     Covers constructed in accordance with the invention also have the further advantage of having fewer bolt holes (and thus required fasteners) than an equivalent all-plastic cover. 
     Additionally, covers constructed in accordance with the invention have the further advantage of providing attaining all of the cost and weight saving advantages of plastic due to the plastic overmold, in combination with the structural and dimensional advantages of metal, due to the metal carrier. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the invention will become more readily appreciated when considered in connection with the following detailed description of the presently preferred embodiments, appended claims and drawings, wherein: 
         FIG. 1  is a perspective view of a valve cover assembly constructed according to a presently preferred embodiment of the invention; 
         FIG. 2  is a perspective view of an arch portion of a metal carrier frame of the valve cover assembly; 
         FIG. 3  is a perspective view of the metal carrier frame; 
         FIG. 4  is a plan view of the assembly of  FIG. 1 ; 
         FIG. 5  is a cross-sectional view taken generally along line  5 - 5  of  FIG. 4 ; 
         FIG. 6  is a rear perspective view of a rear engine cover assembly constructed according to another presently preferred embodiment of the invention; 
         FIG. 7  is a front perspective view of the rear engine cover assembly; 
         FIG. 8  is partially exploded perspective view of a metal carrier frame of the rear engine cover assembly; 
         FIG. 9  is a plan view of the assembly of  FIG. 7 ; and 
         FIG. 10  is a cross-sectional view taken generally along line  10 - 10  of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A cover assembly for an internal combustion engine (not shown), represented here as a valve cover assembly constructed according to a presently preferred embodiment of the invention, is shown generally at  10  in  FIGS. 1 and 4 . The valve cover assembly  10  has a body  12  that may be dome-shaped and elongated to provide a generally trough-shaped structure. The body  12  extends longitudinally between opposite ends  14 ,  16  and laterally between opposite sides  18 ,  20 . The assembly  10  includes a mounting flange  22  that encircles an outer perimeter  23  of the body  12 . Side portions  24 ,  26  of the flange  22  extend along the sides  18 ,  20  of the body  12  and are formed with a plurality of bolt holes  28  for accommodating a corresponding plurality of fasteners (not shown) used to mount the cover  10  to a cylinder head (not shown) of the internal combustion engine. 
     As shown in  FIG. 3 , the valve cover assembly  10  includes a metal reinforcement carrier or frame shown generally at  30 , which may be made of stamped steel, for example. The reinforcement or carrier  30  is overmolded with a plastics material  32  that closes the spaces between members of the carrier  30  and completes the general shape of the assembly  10 . The carrier  30 , being over molded, is at least partially embedded, and shown here as being completely embedded or encapsulated in the plastics material  32 . The carrier  30  serves to provide rigid structural support and dimensional integrity to the plastics material  32 . 
     As shown in  FIGS. 2 and 3 , the carrier  30  includes a plurality of arch-shaped trusses or beams  34  that extend laterally across the valve cover assembly  10  crosswise and generally perpendicular to the longitudinal direction generally between the opposite sides  18 ,  20 . As illustrated, the trusses  34  take the general cross-sectional shape of the body  12  of the assembly  10  and are spaced laterally from another. At least some of the trusses  34  are spaced from the ends  14 ,  16  of the assembly  10 , and thus, reside generally in the mid region of the body  12 . As such, the trusses  34  enable use of a relatively thin-walled layer of the plastics material  32  in comparison to a cover not having trusses, wherein the trusses  34  act to reduce deflection of the cover assembly  10  and add structural integrity to the assembly  10  across its width and over its length. 
     The carrier  30  may further include flange support portions  36 . Preferably, a pair of laterally spaced flange support portions  36  serve to reinforce the mounting flange  22 , and in particular the laterally spaced side portions  24 ,  26  of the flange  22 . The overmolded plastics material  32  surrounds or encapsulates the portions  36 , including an underside mounting surface  38  directly beneath the portions  36 . Accordingly, an exposed surface  39  ( FIG. 5 ) of the overmolded plastics material  32  overlying the frame  30  serves as the sealing surface for engaging a seal gasket (not shown) of the internal combustion engine that is positioned between the cover assembly  10  and the cylinder head (not shown). 
     The flange support portions  36  include a plurality of bolt holes  40  that correspond to the bolt holes  28  of the assembly  10 . As such, the metal carrier  30  surrounds each bolt hole  28  and extends between adjacent bolt holes  28 , providing structural and dimensional support and integrity to the flange  22 . 
     The trusses  34  and flange support portions  36  may be separate or connected to one another as a sub-assembly. As such, the trusses  34  may be fixed to the side flange supports  36 , such as via a weld joint, for example, or, as shown in  FIGS. 3 and 5 , they may be separate and detached from one another. 
     The plastics material of the overmold  32  may be fabricated of a suitable thermoplastics material. The overmold  32  may also be fabricated of a thermoset material. The overmold  32  may be formed of other material as well, including but not limited to rubber, magnesium and aluminum, for example. 
     The metal carrier  30  provides the main support for the assembly  10 , while the overmolded plastics material  32  connects the flange supports  36  and trusses  34  of the carrier  30  together and serves to reinforce the carrier  30  (and also to form the enclosure function of the cover  10 ). To further enhance the structural rigidity of the carrier  30 , and thus, the cover assembly, the trusses  34  and flange support portions  36  of the carrier  30  may include reinforcement ridges, ribs or embossments  42  that extend outwardly from a generally flat plane (P,  FIG. 5 ) traversed by the trusses  34  and flange support portions  36 . The embossments  42  can further act as load limiters about the bolt holes  28  to reduce the possibility of deflection or over compression of the mounting flange  22 . 
     The cover assembly  10  allows die cast covers or relatively thick-walled plastics covers to be replaced with less expensive and thinner-walled metal/plastic composite construction of the present invention. The assembly  10  uses less plastics material than the all-plastics covers and weighs less, while maintaining equivalent or better structural performance than the all-metal covers. Because of the increased structural stiffness provided by the carrier  30 , larger bolt spans between adjacent bolt holes  28  are possible, and thus, the cover  10  can be mounted with fewer fasteners than that required for traditional all-plastic covers. By way of example and without limitation, in a valve cover normally requiring twelve fasteners in an all-plastic thermoset cover, only ten or fewer fasteners would now be required using the present assembly  10 . The assembly  10  also has improved dimensional stability and resistance to creep as compared to an all plastic cover of equivalent application. 
     In  FIGS. 6 and 7 , another aspect of a cover assembly in accordance with the invention, shown as a rear engine cover assembly constructed according to a presently preferred embodiment, is shown generally at  50 . Plastic covers traditionally use a press-in-place style gasket to compensate for the increased amount of deflection and the creep of the plastic over time as compared to a metallic cover. Traditional metal rear covers (such as die cast aluminum) are able to use a flat “LEM” (liquid Eastover molding) gasket, which is less expensive than the press-in-place gasket variety, because of the reduced deflection of the aluminum die casting. Accordingly, if an all plastic cover is provided as a lower cost solution compared to the aluminum die cast cover, the higher priced press-in-place gasket would be needed, and thus, may offset any potential cost savings by using plastic. 
     The carrier/plastic rear cover assembly  50  construction described herein and shown in  FIGS. 6 and 7  allows the lower cost gasket solution (LEM) to be utilized due to the reduced deflection of the cover assembly  50  as compared to an all plastic cover. As such, the overall cost of the assembly  50  in use is reduced in comparison to all plastic covers. As in the valve cover assembly  10  above, by using a stamped metal carrier  52  ( FIG. 8 ) around an outer perimeter  54  and around a crankshaft seal bore  56 , the deflection of the overmolded plastic/metal cover assembly  50  can be reduced. Further, the metal carrier  52  allows a thin wall of standard low cost thermoplastic material to be molded over the metal carrier  52  to form a body  58  of the cover assembly  50 . Another benefit of the stamped steel carrier  52  is the ability to form or incorporate bolt limiters  60  in place. By using the lower cost thermoplastic body  58  with the over molded steel carrier  52 , a less expensive cover assembly results in comparison to those utilizing separate load limiters in combination with thick walled plastics, or all metal covers. 
     The carrier  52  includes a perimeter portion  62  shaped to extend around the outer perimeter  54  of the assembly, and preferably continuously thereabout, and a bore portion  64  shaped to extend around the crankshaft seal bore opening  56 , and preferably continuously thereabout. Both portions  62 ,  64  have ridges, ribs or embossments  66  to stiffen the respective portions  62 ,  64 . The perimeter portion  62  has spaced holes  68  for receipt of the fasteners (not shown), wherein the holes  68  are surrounded by the embossments  66  to assist in reducing deflection, while also acting as bolt limiters. In addition to the embossments  66 , additional load limiting features  60  can be incorporated to further reduce deflection of the assembly  50  upon tightening the fasteners. These load limiting features  60  are preferably exposed even after overmolding. The load limiting features  60  can be made of the same or of a different material than that of the perimeter portion  62 . For example, the perimeter portion  62  can be made of steel, while the load limiting features  60  could be made of stainless steel, by way of example and without limitation. Accordingly, the perimeter portion  62  serves as a carrier for the load limiting features  60 . It should be recognized that the load limiting features  60  could be molded in place via the overmolded body  58 , or they could also be attached to the perimeter portion  62 , such as by way of a weld joint, for example. 
     As such, the cover assembly  50 , although constructed in large part from the lightweight plastics material body  58 , can provide a secure and reliable attachment and remain reliably sealed to the crankcase in use. This is due to the incorporation of the metal carrier  52  into the body  58 , and further made possible by the addition of the load limiting features  60 . 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Technology Classification (CPC): 1