Patent Grant
7040268
The present disclosure relates generally to engine covers, such as valve or rocker covers, and more particularly to an apparatus and method for mounting the engine cover on an engine.
The use of overhead valve and overhead cam engines is well known in the automotive and motorcycle industry. These engines have several distinguishing features, one of which is a valve cover mounted on the cylinder head. The valve cover defines the upper portion of either the rocker box (for overhead valve engines) or the cam case (for overhead cam engines).
The valve cover is typically a cast, stamped, or molded one-piece rigid structure that has a lower peripheral edge corresponding in shape to the upper peripheral edge of the cylinder head. The valve cover is mounted on the cylinder head over the valve drive (e.g., rockers or cams and valves). A sealing gasket is commonly used to seal the joint between the cylinder head and the valve cover.
In general, conventional gaskets require a relatively high compressive load between the members being sealed in order for the gasket to provide an effective seal. For example, a gasket placed between two stationary members, such as an engine block and an oil pan, or an cylinder head and a valve cover, is compressed between these elements. However, while producing an effective seal, these highly compressed gaskets can become a medium for transmitting noise, vibration and harshness (NVH) characteristics between the two members. That is, the vibration load input from one member is easily transferred through either the gasket or direct contact with the other member. Moreover, in these applications that require the high compressive sealing load, the number and placement of fasteners must compensate for deflections of the cover caused by the high loading conditions in order to assure a good seal.
Examples of such conventional gaskets requiring a high sealing load between the members include an elastomeric gasket shaped as an O-ring or similar shape, as well as an edge bond gasket, a carrier gasket, and a rubber coated metal (RCM) gasket. Since all of these conventional gaskets require a high compressive sealing load to assure an effective seal between the members, the effectiveness of vibrational isolation of one member from the other is poor. Another example of a conventional gasket is one formed from a room temperature vulcanization (RTV) located between the two members. The RTV is applied as a liquid in a thin layer and cures when exposed to air. For effective sealing with the RTV, however, it requires a hard mount between the members, which also provides poor vibration isolation.
It is known in the art relating to engine valve and rocker covers to provide a gasket and grommet mounting in a noise isolation system which interrelates the sealing performance and noise isolation in a robust cover design. Noise isolation is provided by mounting a cover with a grommet at each hold down bolt location and by a peripheral molded seal or gasket between the cover and the engine cylinder head or block which separates the cover from direct metal to metal contact (see
Accordingly, a cover mounting system which maximizes NVH isolation, provides an adequate uniform sealing function and minimizes structural requirements is desired.
Disclosed herein is a sealed cover assembly for a fluid-containing cavity of an engine includes a cover including a fluid-containing wall with a peripheral edge having a sealing surface adapted to oppose a corresponding sealing surface of the engine, and a plurality of mounting openings in the peripheral edge; a reaction pad adjacent each of the openings and disposed at the peripheral edge on an opposite surface of the sealing surface around a perimeter defining the cover; a brace disposed against the reaction pad around the perimeter defining the cover; and mechanical fasteners extending through the reaction pad and the brace for securing the cover to a mating edge of the engine cavity, the fasteners when engaged providing substantially equal compression forces on the reaction pad via the brace and supporting the cover sealing surface with a predetermined gap from the cavity mating edge for engagement with a compliant sealing material disposed between the surfaces.
An engine cover assembly defining a fluid-containing cavity is further disclosed, which includes an engine component including a sealing surface defining an edge of the cavity; a cover including a fluid-containing wall surrounded by a peripheral edge and having a sealing surface opposing the sealing surface of the engine component, and a plurality of mounting openings in the wall; a reaction pad adjacent each of the openings and disposed at the peripheral edge on an opposite surface of the sealing surface around a perimeter defining the cover; a brace disposed against the reaction pad around the perimeter defining the cover, the brace including a plurality of height limiters depending therefrom and aligned with each of the openings; and mechanical fasteners extending through the reaction pad and each height limiter for engaging the engine component for securing the cover to the engine component, the fasteners when engaged providing equal compression forces on the reaction pad via the brace and supporting the cover sealing surface with a predetermined gap from the cavity mating edge for engagement with a compliant sealing material disposed between the surfaces.
Also disclosed is a method for a method for sealing an engine cavity, which includes configuring a cover including a fluid-containing wall with a peripheral edge having a sealing surface adapted to oppose a corresponding sealing surface of an engine; configuring a plurality of mounting openings in the peripheral edge; disposing a reaction pad adjacent each of the openings and around at the peripheral edge on an opposite surface of the sealing surface around a perimeter defining the cover; disposing a brace against the reaction pad around the perimeter defining the cover; and extending mechanical fasteners through the reaction pad and the brace for securing the cover to a mating edge of the engine cavity, the fasteners when engaged providing equal compression forces on the reaction pad via the brace and supporting the cover sealing surface with a predetermined gap from the cavity mating edge for engagement with a compliant sealing material disposed between the surfaces.
The above-described and other features are exemplified by the following figures and detailed description.
Referring now to the figures, which are meant to be exemplary embodiments, and wherein like elements are numbered alike:
The present disclosure provides a cover assembly for an engine that provides a uniform standoff height around a perimeter defining the cover assembly that prevents hydraulic lift of the cover assembly when a gasket between the cover assembly and engine heats up and expands as a thick fluid medium. The uniform standoff height provides a space for the gasket to flow without hydraulically lifting the cover assembly from the engine. The standoff height also allows isolation of, or at least limits, engine noise radiating from the cover assembly dependent on a height of a limiter and/or reaction pad material intermediate the limiter and the cover assembly. The cover assembly eliminates mid-span deflection of the cover assembly intermediate bolt bosses with a uniform reaction load around a perimeter of the cover assembly.
It will be noted in the above design that the standoff height is zero and that engine noise radiates from cover 12 due to full perimeter contact of lip 14 with the cylinder head. Furthermore, if gasket 18 fills groove 16, gasket 18 will hydraulically lift the joint potentially affecting the integrity of the gasket 18 and/or cover 12. Lastly, mid-span deflection of cover 12 (e.g., intermediate bolt bosses 20) is controlled by the structure of cover 12. In other words, cover 12 deflects less when cover 12 is structurally stiffer using a metal instead of plastic (e.g., a thermoset), for example. It will be recognized that less mid-span deflection occurs if each span between contiguous bolt bosses 20 is reduced by increasing a number of bolt bosses 20 and corresponding number of mechanical fasteners 22.
In this manner, it will be noted that the above-described design provides a controlled standoff height determined by a length of bosses 32 extending below bottom surface 36 defining lip 14. Thus, engine noise radiates from cover assembly 30 due to contact of the cylinder head with bosses 32 while engine noise is dampened by gasket 18 in the mid-spans 40 between contiguous bosses 32. Furthermore, gasket 18 will not hydraulically lift the joint because of the standoff distance in the mid-spans 40 provided by bosses 32 allowing expansion of gasket 18 in the joint intermediate contiguous bosses 32 corresponding to the mid-spans. Lastly, mid-span deflection of cover 12 (e.g., intermediate bolt bosses 20) is controlled by the structure of cover 12 as described in
However, a sealing pressure of gasket 18 varies with the bolting pattern in this configuration. Thus, the cover standoff height is uncontrolled around a perimeter of cover 12 due to individual compression variations of each grommet 54. As such, engine noise radiating from cover assembly 50 varies with the compression of the grommets 54 and gasket 18. Furthermore, uneven compression may affect the long term integrity of gasket 18 and grommets 54. As before, mid-span deflection is controlled by cover structure.
Although the drawings depict groove 16 in sealing surface 36, groove 16 is optional. The sealing surface 36 of cover 12 optionally includes a groove 16 into which some of gasket 18 is displaced so that the interaction with the groove prevents the sealing material or gasket 18 from being easily dislodged from the gap between the sealing surfaces and maintains the sealing material in position under all conditions of operation of the engine.
Bar 116 is vertically oriented such that a first cylinder 125 defining each height limiter 120 extends from a broad externally exposed surface defining bar 116. In this vertical orientation, bar 116 is less susceptible to bending when a vertical force is applied via mechanical fasteners 22 and allows the vertical force to be uniformly supplied about a perimeter defining bar 116. In an exemplary embodiment, bar 116 and each height limiter 120 is made of steel for simplicity in fabrication of brace 110 and cost. However, any material is contemplated that is suitable to provide a uniform load on lip 14 about a perimeter thereof without significant deflection in mid-span regions between contiguous mechanical fasteners 22.
Referring to
In an exemplary embodiment shown in
For mounting of the cover assembly 100 on the cylinder head 140, cooperating threaded openings 138 are provided in the cylinder head into which the ends 164 of the bolts are threaded to mount the cover 12 onto the cylinder head 140. Prior to the assembly step, a sealing material or gasket 18 is disposed in groove 16 of cover 12. The cover assembly 100 is then positioned opposite the engine sealing surface 142. The bolts 22 are then threaded into their corresponding openings 138 in the cylinder head and tightened down until the bolt head flanges 162 engage the sleeves 150 and the opposite second ends 158 engage sealing surface 142 of cylinder head 140, which establishes the predetermined compression of gasket 18 along with partial compression of reaction pad 124. In an exemplary embodiment, if reaction pad 124 and gasket 18 have a similar spring rate, compression of the gasket is equal to compression of the reaction pad so that the mounting forces applied thorough the gasket 18 and reaction pad 124 on the cover 12 are balanced. The cover is thereby retained in a position with its sealing surface 36 spaced outward, by a predetermined gap dimension or standoff height, from the sealing surface 142 of the cylinder head.
It will be further recognized that since reaction pad 124 is continuous about a perimeter of cover 12 with a uniform load provided by brace 110, reaction pad 124 may be softer or have a lower durometer than the grommets 54 of
Reaction pad 124 is preferably molded as a one-piece integral member. The hardness and compression rate of the reaction pad material are preferably uniform throughout the molded reaction pad 124 so that both sides defining a thickness of the grommet compress equally from an extended initial length shown in
As described above, cover assembly 100 eliminates mid-span deflection due to the uniform reaction load from brace 110 around a perimeter defining cover 12. In other words, brace 110 provides all of the structural load requirements that gasket 18 places on cover 12. Since a uniform reaction load about the perimeter of cover 12 is provided by brace 110, the cover structure of cover 12 is only required to maintain its shape.
The design of the cover assembly promotes a long life installation since the position of the cover is balanced by gasket 18 and reaction pad 124 at all attachment points so that no distortion or rotation of the cover due to gasket reaction loadings occurs. Thus, alternative cover materials which provide ideal mass and cost considerations may be utilized without concern as to substantial stresses placed on the cover by having to load a seal material against the cylinder head. For example, this allows cover 12 to be manufactured from a recyclable thermoplastic instead of a non-recyclable thermoset material currently employed or a metal. Using a recyclable thermoplastic cover 12 results in significant cost savings.
As the name suggests, a thermoset is a material (such as rubber) that cures or hardens (sets) into a given shape, generally through the application of heat (a thermal increase). Curing (also referred to as vulcanizing) is an irreversible chemical reaction in which permanent connections (known as cross-links) are made between the material's molecular chains. Thermoset polymers outperform other materials, such as thermoplastics, in a number of areas, including mechanical properties, chemical resistance, thermal stability, and overall durability. For these reasons, thermoset parts tend to make more effective seals. However, a cured thermoset material will not remelt or otherwise regain the processibility it had before being cured, as curing changes the material forever.
A thermoplastic material softens (becomes pliable and plastic) when heated, but it does not cure or set. A thermoplastic often begins in pellet form, then becomes softer and more fluid as heat increases. This fluidity allows it to be injected under pressure from a heated cavity into a cool mold. As it cools, the thermoplastic will harden in the shape of the mold, but there is no chemical curing at work. No cross-links are formed as with a thermoset material. The changes seen in the thermoplastic are purely physical and, with the reapplication of heat, wholly reversible. A thermoplastic material can therefore be reprocessed many times, though continual recycling will eventually degrade the polymer. Furthermore, by using brace 110 in conjunction with a thermoplastic cover 12, the strength lost by using a thermoplastic instead of a thermoset may be regained and significant cost savings are realized by using a recyclable thermoplastic.
While the exemplary cover assembly design illustrated involves a number of specific design considerations, the brace and cover concept can be utilized with other cover designs to isolate a cover of any type from an associated engine component on which it is mounted. If desired, the integral height limiters 120 could be replaced by separate individual height limiters 120 attachable to bar 116 forming a variable height limiter assemblies having equal compression characteristics to provide the balanced mounting assembly of the invention. However, a single height limiter fixedly attached to the bar 116 for each mounting location is preferred for ease of manufacture, assembly and parts retention. If necessary, a variable thickness reaction pad 124 could be utilized to perform the same function of the separate individual height limiters of variable height in place of the variable height limiter design.
While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to a particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5255647 | Kiczek | Oct 1993 | A |
| 5323740 | Daily et al. | Jun 1994 | A |
| 6591801 | Fonville | Jul 2003 | B1 |
