Crankcase for an internal combustion engine

Details Crankcase for an internal combustion engine Crankcase for an internal combustion engine

1999-11-05

2001-05-29

Kamen, Noah P. (Department: 3747)

Internal-combustion engines

Frame construction

Horizontal cylinder

C123S1950HC

Reexamination Certificate

active

06237558

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a crankcase for an internal combustion engine, with crankshaft main bearing walls including crankshaft main bearing blocks, and side walls with skirtlike extensions, the side of each main bearing block being at least partially separated from the inner surfaces of the side walls by a recess.
DESCRIPTION OF THE PRIOR ART
In AT 398 608 B a crankcase is described in which the main bearing blocks are partially stress-relieved by recesses running along the ribs of the crankcase so that the propagation of deformations due to gas or mass forces towards the side walls of the crankcase will be prevented. The recesses have a constant curvature at the point of maximum depth. The drawback of this design is that peak stresses due to the forces of the main bearing bolts and the gas force will accumulate in one point of the recess, which may lead to critical stress values.
SUMMARY OF THE INVENTION
It is an object of this invention to avoid the above disadvantages and reduce the stresses produced by mechanical loads in a crankcase of the above described type.
According to the invention this is achieved by providing the recess with a curved contour, at least in sections, whose curvature increases continuously from an inner section in the area of the side face of the main bearing block to an outer section in the area of the inner surface of the side wall. It is a special advantage if the contour has a larger curvature radius in at least one area of maximum mechanical stress resulting from gas forces essentially acting in the direction of the cylinder axis and/or forces arising from the main bearing bolts, than in areas which are subject to less mechanical load. Calculations have shown that it is possible in this way to reduce critical peak stresses resulting from the added stresses due to holding forces and gas forces. Whereas the zones of critical stress have maximum curvature radius, less critical areas may have a smaller curvature radius.
In order to keep the width of the recesses as small as possible even if the mechanical load is to be very small, the the contour has a curvature radius that is larger in an area at the side of the main bearing block than in the area of an inner surface of a side wall. The contour may have its smallest curvature radius in the area where the recess has its maximum depth.
Preferably, the contour of the recess at the point of maximum depth should be composed of at least two circular arcs with different radii, the arc next to the inner surface having the smallest radius. It may be provided in an enhanced variant of the invention that the contour is composed of at least three circular arcs with different radii.
It has been found that critical peak stresses can be optimally reduced if the contour, or at least sections thereof, assume the shape of a conic section, such as an ellipse, hyperbola or parabola. The conic section could be approximated by circles, i.e., oval arches for approximation of an ellipse. In short-stroke engines with small crankcase width the main axis of the conic section should advantageously form an angle with a parallel of the cylinder axis of about 0° ±60°, and preferably, 0° ±30°, preference being given to an embodiment wherein a vertex of the conic section on the main axis is positioned in or near the area of maximum depth of the recess, and more preferably on the side of the outer section.
If the contour, or at least sections thereof, assume the shape of an ellipse, the curvature radius of the inner section of the contour preferably corresponds to the curvature radius of the ellipse in the area of a small semi-axis.
In another low-stress variant of the invention the proposal is put forward that the contour, or at least sections thereof, be configured as a spiral line or involute.


REFERENCES:
patent: 4582028 (1986-04-01), Wagner et al.
patent: 4773366 (1988-09-01), Seidl et al.
patent: 4876998 (1989-10-01), Wunsche
patent: 5107809 (1992-04-01), Suh
patent: 5868110 (1999-02-01), Betsch
patent: 314912 (1974-04-01), None
patent: 398608 (1995-01-01), None
patent: 2153258 (1972-08-01), None
patent: 0463314 (1992-01-01), None
patent: 0553069 (1993-07-01), None
patent: 09137749 (1997-05-01), None

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