Expansible chamber devices – Piston – Open-ended hollow skirt type
Reexamination Certificate
1999-10-07
2001-06-12
Look, Edward K. (Department: 3745)
Expansible chamber devices
Piston
Open-ended hollow skirt type
C092S231000
Reexamination Certificate
active
06244161
ABSTRACT:
BACKGROUND OF THE INVENTION
In general, this invention relates to a piston and to a method of forming the piston. More specifically, but not exclusively, this invention is directed to a temperature-resistant piston head formed of a high temperature-resistant material and to a method of forming the temperature-resistant piston head.
Typical piston heads are formed of a single material that is selected to provide the requisite mechanical strength at the temperatures normally experienced in internal combustion engines. These materials are typically forged or cast steel alloys, which are subsequently heat-treated to improve their high temperature and temper resistance.
One prior art piston head includes a piston crown section and a connecting rod section. A friction weld joins the two sections into an assembled piston head. The two sections are formed of the same forged or cast steel alloy material to facilitate friction welding and subsequent heat treatment.
To improve performance, it is becoming increasingly desirable to operate internal combustion engines at higher temperatures. This desire is especially prominent in relation to larger diesel engines used in electrical power generation applications. Unfortunately, existing pistons tend to more readily oxidize, particularly at the combustion bowl rim, which typically is subjected to the highest operating temperature. The combustion bowl rim, and the piston head in general, may suffer from a loss of hardness if exposed to more extreme temperatures. As a result, piston head failure may become more frequent.
Thus, there is a need to provide pistons capable of withstanding the extreme thermal and mechanical loading likely to result from new, higher performance engines. The present invention addresses these needs.
SUMMARY OF THE INVENTION
There is provided in accordance with one form of the present invention, a unique piston capable of withstanding the thermal stress and mechanical loading of high performance engines.
In another form, the piston head includes a first portion and a second portion connected by a friction weld. The first portion is formed of high temperature oxidation-resistant material. In one embodiment, the first portion comprises, in weight percent, about 0.1 to about 0.5% carbon, up to about 0.6% manganese, about 4 to about 6% chromium, about 0.45 to about 0.65% molybdenum, up to about 0.5% nickel and the balance iron and incidental impurities. The second portion of the piston head is preferably formed of steel alloy capable of withstanding the mechanical forces generated from combusting fuel. The steel alloy of the second portion can comprise, in weight percent, about 0.30 to about 0.55% carbon, about 0.4 to about 01.10% magnesium, about 0.40 to about 1.25% chromium, about 0.15 to about 0.45% molybdenum, up to about 0.4% silicon, up to about 2 wt % Ni and greater than 90% iron; however, the second portion may alternatively be formed of a different material.
In still another form there is provided in accordance with the present invention a method of forming a piston head. The method comprises providing a first portion that includes a high temperature-resistant steel alloy and a second portion that includes a second material of a steel alloy, and friction-welding the first portion to the second portion. The first and second portions can be machined to provide a wide variety of piston design configurations for a piston crown and a piston rod connecting member, respectively.
Further objects, features, aspects, forms, embodiments, advantages and benefits shall become apparent from the description and drawings contained herein.
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Myers Martin R.
Ribeiro Carmo
Cummins Engine Company, Inc.
Leslie Michael
Look Edward K.
Woodard Emhardt Naughton Moriarty & McNett
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