Internal combustion engine

Details Internal combustion engine Internal combustion engine

1999-10-15

2001-01-09

McMahon, Marguerite (Department: 3747)

Internal-combustion engines

Particular piston and enclosing cylinder construction

Piston

C123S659000, C123S661000

Reexamination Certificate

active

06170455

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is related to German Application No. 198 49 913.2-13 filed in Germany on Oct. 29, 1998, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improved piston for an internal combustion engine.
2. Description of Related Art
The prior German DT 26 07 561 A1 corresponding to U.S. Pat. No. 4,170,966 issued Oct. 16, 1979 to Schmidt entitled “Mixture-Compressing Internal Combustion Engine, Especially Four-Cycle Engine” discloses an internal combustion engine of the generic type with recesses formed in the piston crown of the piston to improve the efficiency of combustion and thus reduce hydrocarbon emissions.
Further references which show internal combustion engines with recesses and depressions formed in the piston crown of the piston are German DE 196 24 227 A1, and DE 29 34 615 A1 and U.S. Pat. No. 3,797,466.
In general, piston configurations with recesses or depressions in the piston crown are used to bring about flow effects including swirling flows of various kinds in the combustion chamber it being the intention to improve the mixing of air and fuel and thus to improve homogenization of the fuel/air mixture, thus increasing combustion efficency.
There is a fundamental distinction between two different types of flow in a combustion chamber: swirling flow which is a vortical motion of the fuel/air mixture about the longitudinal axis of the cylinder of the internal combustion engine; and tumbling flow, on the other hand, which is a vortical motion about an axis parallel to a transverse axis of the cylinder. The aim of the recesses mentioned above is to reinforce the degree of turbulence within the combustion chamber defined by the cylinder or to otherwise deflect such flows.
A disadvantage with the known embodiments of recesses in the piston crown of the pistons of internal combustion engines is the still relatively poor mixing and the consequent stratification of the fuel/air mixture in the combustion chamber and the associated increase in the tendency to knock, despite the efforts made to bring about flow effects.
SUMMARY OF THE INVENTION
It is therefore the object of the present invention to provide an internal combustion engine in which air and fuel are mixed externally of the combustion chamber and a piston having a crown configured in such a way that the tumbling flow of the air/fuel mixture about a transverse axis is deflected or influenced in such a way that: good mixing of the fuel/air mixture is thereby achieved; unwanted stratification of the fuel/air mixture in the cylinder is prevented; and thus the tendency to knock is reduced.
According to the invention, a piston crown of a piston of an Otto-type internal combustion engine includes a substantially crescent-shaped depression which is substantially symmetrical with respect to an axis of symmetry of a cylinder bore housing the piston.
The piston's crown configuration of the subject invention includes a crescent-shaped depression so that the fuel/air mixture can be more accurately directed to the region adjacent the spark plug by tumbling flow during the compression process. The piston crown configuration produces better mixing and homogenization of the fuel/air mixture and an associated reduction in the tendency to knock and also reduces the average distance between the spark plug and the fuel/air mixture in the combustion chamber. In this arrangement, the fuel is mixed with the air required for combustion outside the cylinder, this being referred to as external mixture formation, by intake-pipe injection, for example.
The arrangement according to the subject invention including the crescent-shaped depression in the piston crown of the piston permits space for positioning more than one spark plug and furthermore allows the combustion chamber to be made more compact. This produces a smaller ratio of surface area to volume of the combustion chamber, i.e. to a smaller eccentricity and to a smaller distance between the cylinder wall and the spark plug thus resulting in a more compact combustion chamber which is less sensitive to knock. The above features increase the rated output of the engine while keeping the same displacement of the internal combustion engine and allows fuel consumption to be reduced during part-load engine operation.


REFERENCES:
patent: 4170966 (1979-10-01), Schmidt
patent: 4294207 (1981-10-01), May
patent: 4366789 (1983-01-01), Eckert
patent: 5092289 (1992-03-01), Bloschies et al.
patent: 5230321 (1993-07-01), Lambert et al.
patent: 6019079 (2000-02-01), Sakurahara et al.

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