Piston with a reinforcing insert

Details Piston with a reinforcing insert Piston with a reinforcing insert

1995-06-23

1996-10-01

Argenbright, Tony M.

Internal-combustion engines

Precombustion and main combustion chambers in series

Piston carried precombustion chamber

92213, 1231936, F02B 2306, F02F 326, F02F 304

Patent

active

055603343

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention refers, in general, to a new construction for pistons used in internal combustion engines and, more particularly, to a new construction for that type of pistons incorporating a reinforcing insert, usually called composite, in order to increase the strength of the piston at those portions that are submitted to higher stresses.


BACKGROUND OF THE INVENTION

The high thermo-mechanical stress to which the piston of more advanced engines are submitted led to the need of incorporating local reinforcements, in order to maintain the structural integrity of the aluminum pistons.
Particularly at the region defined by the combustion chamber edge, where the highest temperatures and thermo-mechanical stresses take place, in order to increase the local strength of the aluminum alloy of said pistons, it is common to incorporate porous ceramic inserts that are infiltrated by the aluminum base alloy. As a result from the manufacturing process used for obtaining said insert, usually the squeeze casting process for aluminum alloys, a composite of high structural strength is produced.
Due to the characteristics of the reinforcing material, the thermal expansion of the composite material is inferior to that of the base material of the piston (aluminum alloy).
In case the insert presents the usual annular shape defining the peripheral wall of the piston combustion chamber, a serious problem occurs at the interface between the low expansion material of the insert and the piston remaining material made of aluminum alloy of higher expansion. Due to the difference between the thermal expansion coefficients of both materials, there occur stresses, resulting from the difference between the expansion of both materials under the same temperature.
Since the insert is in the form of a ring, which presents a generally rectangular cross section, which is disposed around the piston combustion chamber and which is projected practically throughout the whole height of the latter, from the upper end face of said piston, the interface defined between the lower end face of the insert and the adjacent radial face of the piston material made of aluminum alloy is disposed at a region submitted to high temperatures, as said region is close to the bottom of the piston combustion chamber.
The high temperatures at the piston region defined along the radial extension of said lower interface of the insert tend to force the piston aluminum alloy to expand radially, at values different from those of the corresponding radial thermal expansion of the insert material, thus demostrating the occurrance of the stresses mentioned above, which reach values sufficient to cause cracks and even ruptures on the piston aluminum alloy.


DISCLOSURE OF THE INVENTION

The present invention has the objective of providing a new construction for a piston of this type, which avoids or at least minimizes the occurrance of the above cited stresses, without affecting the structural integrity of the piston.
The piston object of the present invention is generally cast in aluminum alloy, presenting a top face provided with a recessed combustion chamber, which has a peripheral lateral wall defined by the annular insert. According to the invention, the annular insert presents an internal end face with a radial extension that is substantially smaller than the radial extension of an opposite external end face of the annular insert, the radial thickness of the annular insert varying along the profile of the external peripheral face, in order to maintain a value required for the structural reinforcement of the piston at the region where the insert is applied.
With the constructive arrangement cited above, the insert may present a portion of its extension, adjacent the external end face, with a larger thickness, which is necessary for achieving the desired structural reinforcement of the piston at this end face region, which surrounds the combustion chamber and which is subjected to high thermal and mechanical efforts, and also to high tempera

REFERENCES:
patent: 2473254 (1949-06-01), Morris
patent: 3596571 (1971-08-01), Hill et al.
patent: 4742759 (1988-05-01), Hayakawa
patent: 5013610 (1991-05-01), Suzuki
Patent Abstracts of Japan, vol. 8, No. 227 (M-332) (1664), Oct. 18, 1984, abstract of JP-A-59-108849.
Patent Abstracts of Japan, vol. 10, No. 62 (M-460) (2119), Mar. 12, 1986, abstract of JP-A-60-206958.

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