Internal-combustion engines – Frame construction – Horizontal cylinder
Reexamination Certificate
2000-09-21
2001-10-30
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Frame construction
Horizontal cylinder
C123S1950HC
Reexamination Certificate
active
06308680
ABSTRACT:
TECHNICAL FIELD
The present invention relates to bearing supports for a main bearing in an internal combustion engine.
BACKGROUND OF THE INVENTION
Mass reduction is a major goal in engine design. Therefore it is known to substitute aluminum for iron in certain engine components. As a common example, automotive engine blocks may be constructed with all aluminum or other light alloys. One drawback in some applications is that commonly employed aluminum alloys have a much higher coefficient of thermal expansion (CTE) than iron. For example, cast iron has a CTE of about 12×10
−6
/K, whereas 380 aluminum has a CTE of about 21×10
−6
/K, a factor of almost two. Therefore in the case where aluminum bearing caps support a ferrous crankshaft, the aluminum bearing caps thermally grow at a greater rate than the crankshaft as the engine operating temperature increases. This results in an increased bearing clearance and potentially unacceptable bearing life and noise generation. Greater bore clearances require larger capacity lubrication systems to compensate for oil leakage past the main bearings and to maintain adequate oil film thickness on the bearings.
A second drawback in certain applications is that commonly-employed aluminum alloys have a lower elastic modulus and strength relative to ferrous materials. This reduction may cause durability challenges, especially with high bearing loads that are typical with high output, supercharged, and diesel applications.
One solution to the thermal expansion issue, as described in U.S. Pat. No. 5,203,854, is to produce an aluminum bearing support cast with an iron core adjacent to the crankshaft bore to provide comparable coefficients of thermal expansion between the crankshaft and the bearing cap. It is proposed that the bearing clearance does not significantly vary over the range of operating temperatures and therefore noise generation is reduced. The disadvantage is that substituting aluminum with a ferrous insert involves a mass penalty for the engine.
The purpose of the present invention is to provide a main bearing support which has a CTE comparable to the ferrous crankshaft it supports, is more mass efficient than aluminum, and has a greater factor of safety than a ferrous inserted, aluminum support due to lower strains from a higher elastic modulus.
SUMMARY OF THE INVENTION
The present invention is for an internal combustion engine having an aluminum engine block, a ferrous crankshaft, and main bearing supports comprised entirely of a binary alloy of beryllium and aluminum. The beryllium-aluminum alloy has the following material characteristics: low CTE comparable to iron alloy; high strength comparable to iron alloy; and low density compared to iron and aluminum.
For example, beryllium-aluminum alloy with 62% beryllium has a CTE of approximately 14×10
−6
/K, which is comparable to iron alloy. This material selection for the bearing supports ensures that a tighter crankshaft bore tolerance may be maintained as compared to an engine with all aluminum or other light alloy supports through the engine operating temperature range. This is due to comparable thermal rates of expansion of the ferrous crankshaft and beryllium-aluminum bearing supports, which are approximately half as great as that of aluminum. A tighter crankshaft bore tolerance will increase bearing life as there is reduced oil leakage and therefore less wear of the bearings and/or allow for a smaller more efficient oil pump to be used. Further, a tighter bore tolerance may reduce noise generation.
The modulus of beryllium-aluminum is 192 GPa as compared to 69 GPa for aluminum, or 120 GPa for iron. Higher strength bearing supports reduce strain experienced during engine operation and therefore increase the life of the part by reducing stresses due to deflection. To generate equivalent stresses as an iron or aluminum bearing support, a smaller beryllium-aluminum support may be employed, thereby reducing the amount of material required, as the superior modulus compensates for the smaller part. Additionally, the smaller support could provide for improved casting as the parent metal would more fully envelop the support.
The density of 62% beryllium-aluminum alloy is 2.10 g/cm
3
as compared to 7.25 g/cm
3
for iron, or even 2.71 g/cm
3
for aluminum. The low density therefore provides a mass savings over a ferrous inserted aluminum support or even an all aluminum support.
Therefore main bearing supports composed of such a beryllium-aluminum alloy provide a combination of low mass, high strength, and dimensional stability of the crankshaft bore. The relatively high cost of beryllium-aluminum alloy may limit its use to high performance and luxury applications in the near term, but it may have increased commercial applicability with market adjustments.
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patent: 4889435 (1989-12-01), Gojon
patent: 4930910 (1990-06-01), Mori et al.
patent: 5038847 (1991-08-01), Donahue et al.
patent: 5129444 (1992-07-01), Bafford
patent: 5203854 (1993-04-01), Nilsson et al.
patent: 5501529 (1996-03-01), Cadle et al.
patent: 5609422 (1997-03-01), Mueller et al.
patent: 5816710 (1998-10-01), Warwick et al.
patent: 6223713 (2001-05-01), Moorman et al.
General Motors Corporation
Hargitt Laura C.
Hodges Leslie C.
Huynh Hai
Kamen Noah P.
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