Internal-combustion engines – Frame construction – Horizontal cylinder
Reexamination Certificate
2001-10-08
2002-11-12
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Frame construction
Horizontal cylinder
Reexamination Certificate
active
06478004
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates to reciprocating piston internal combustion engines and, in particular, to a crankcase front cover for an automotive reciprocating piston internal combustion engine.
In the most recent three decades there has been a major push to increase the fuel economy of automotive vehicles. One technical trend to increase automotive fuel economy is to make the vehicle lighter. An excellent example of an automotive component that has been made lighter is the engine. Engine blocks are now typically fabricated from cast aluminum rather than prior cast iron. Many components, for example the intake manifold and valve covers are now fabricated from polymeric materials such as injection or blow molded plastics that can withstand high temperatures.
A reciprocating piston internal combustion engine has an engine block with a crankcase that is open along a front end to allow for installation of a crankshaft. The crankcase is enclosed by a fastener connected engine front cover that has a lower opening to allow for passage therethrough of the extreme front end of the crankshaft. The front cover has two functions. First, it provides a sealing pressure boundary for the crankcase to prevent escape of the lubricating oil from the engine. Second, it serves as a mounting member for mounting directly or via brackets, several engine belt-driven components, such as the air conditioning compressor, power steering pump, idler arms or other various pulleys which are typically engaged by a serpentine belt arrangement.
When an automotive engine is running, the engine cylinder block and heads induce vibration into the front cover. Accordingly, the front cover becomes a front sound pressure generator of the engine. It is often desirable in luxury class vehicles to minimize the sound emanating from the engine. Empirical studies have shown divergent strategies can minimize sound pressure generation from engine front covers. A first strategy is to provide a front cover with multiple pieces that is very stiff. The stiffness significantly increases the cover″s natural frequency. This approach has been found to function but is expensive compared to a one-piece cover. Also, since the crankcase opening is not covered by one continuous piece, there are more possible leak paths.
A second strategy to minimize sound pressure generation is to significantly lower the natural frequency of the front cover, particularly in the vicinity of the crankcase opening. The efficiency of sound transmission from a plate to the atmosphere is inversely proportional to the natural frequency of the plate. Therefore, lowering the natural frequency of the engine front cover can synergistically lower the sound pressure generation of the front cover. Lowering the frequency of vibration of the cover requires a very thin cover. However, providing the structural requirements of an engine front cover for its function of mounting engine belt-driven components limits the selection of suitable materials that have a lower natural frequency and the required strength. One practical material that offers the aforementioned requirements is magnesium. However, magnesium is highly cost prohibitive for such an application.
It is desirable to provide a front cover for a reciprocating piston internal combustion engine that is lighter than the current cast aluminum or iron covers. It is also desirable for such a front cover to have increased sound attenuation characteristics when compared to engine covers which are typically fabricated from stamped steel or cast aluminum.
SUMMARY OF INVENTION
In a preferred embodiment, the present invention brings forth a cover providing a boundary for a crankcase opening of an internal combustion engine. The cover includes a polymeric membrane sealably enclosing the crankcase opening. The polymeric membrane has an opening for passage of the crankshaft therethrough. The polymeric membrane has a plurality of fastener apertures along its perimeter to connect it to an engine crankcase. A metal portion is provided positioned adjacent to upper portions of the polymeric membrane and is bonded thereto. The metal portion has fastener apertures aligned with the fastener apertures of the polymeric membrane. The metal portion provides a platform for mounting pulleys powered by an engine powered belt. The cover provided herein has a natural frequency significantly lower than prior art metallic crankcase covers.
The present engine cover with its lower natural frequency, particularly in the vicinity of the crankshaft opening, has significant sound attenuation properties. Since the polymeric membrane is one piece, no additional leak paths are created, as with prior steel or cast aluminum covers.
Other advantages of the present invention will become more apparent to those skilled in the art from a reading of the following detailed description and reference to the drawings.
REFERENCES:
patent: 4122820 (1978-10-01), Ryberg
patent: 4498433 (1985-02-01), Ogawa
Deng Eddy D.
Grawi Franklin Lawrence
Stickler Mark L.
Werth Rich
Argenbright Tony M.
Ford Global Technologies Inc.
Harris Katrina B.
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