Internal-combustion engines – Cooling – Internal cooling of moving parts; e.g. – hollow valves,...
Patent
1998-06-26
1999-09-07
Yuen, Henry C.
Internal-combustion engines
Cooling
Internal cooling of moving parts; e.g., hollow valves,...
1231936, F01P 306
Patent
active
059470658
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a cast light-metal piston for internal combustion engines, with a cooling channel in the piston head.
A piston of such type is known from DE-PS 37 21 021, where the ring-shaped cooling channel tube consists of an aluminized or alfine-treated material with high thermal conductivity. The butt ends of the tube are joined with each other by a welding process in order to obtain flawless sealing. Due to the aluminizing of the cooling channel tube and the welding of the ends of the tube, however, this represents a more expensive solution.
It is known, furthermore, to position rings or spirals in the casting mold and to pour the material around such elements. The drawback of this solution is that the heat transfer is obstructed. Due to the different coefficients of thermal expansion of steel and aluminum, a slit develops between the cooling channel and the piston at operating temperature, such slit obstructing the flow of heat.
The invention deals with the problem of enhancing the heat transfer between the material of the piston and the cooling channel and of reducing the manufacturing cost of the latter. According to the invention said problem is solved by the features of the characterizing part of patent claim 1.
Advantageous further developments of the invention are the objects of the dependent claims.
As with the cooling channel known from the state of the art, which is made from steel tube, a slit develops at operating temperature between the basic piston material and the sheet metal because of the different coefficients of thermal expansion. However, said slit extending in the cooling channel over at least part of its circumference between the cooling channel and the basic piston material fills with cooling oil. Such oil-filled slit leads to significantly superior heat transfer than a slit filled with air.
Another advantage of the sheet-metal cooling channel as defined by the invention is that such a cooling channel can be manufactured inexpensively by a sheet metal reshaping process, and that the cost for pretreating the cooling channel and for sealing it is omitted. The cooling channel can be shaped in this connection by deep-drawing with subsequent flanging.
The coefficient of thermal expansion of the material of the cooling channel advantageously amounts to between 10 and 17.multidot.10.sup.-6 1/K and is thus clearly lower than the one of the basic piston material.
The width of the slit in the cooling channel, such slit extending over at least part of its circumference, is preferably between 0.08 and 0.5 mm; the particularly preferred range is 0.08 to 0.2 mm. In general, the width of the slit has to be dimensioned in such a way that the melt cannot flow through it into the interior of the cooling channel as material is being poured around the latter. The sealing function can be enhanced further in that in addition to a relatively narrow width of the slit, the butt ends of the metal sheet rest one on top of the other, overlapping each other.
The invention is explained in greater detail in the following with the help of two drawings:
FIG. 1 shows a semisectional view of the piston as defined by the invention; and
FIG. 2 shows a cross section through the cooling channel as defined by the invention, with a butt joint.
A light-metal piston 1 made from AlSi-alloy with a piston ring groove arrangement 2 in piston head 3, whose first ring groove 4 is reinforced by a ring carrier 5, has a ring-shaped cooling channel 6 within the zone behind piston ring groove arrangement 2. Along its circumference, said cooling channel has a narrow slit 7 permitting passage of oil. The slit is not visible in the present representation. Said cooling channel 6 is manufactured by a metal sheet reshaping process.
For receiving cooling channel 6 in the course of casting of light-metal piston 1, two holding sleeves 8 (shown displaced in FIG. 1) are employed, said sleeves being supported in the casting die. Said holding sleeves 8 are arranged with respect to the circumference of cooling channel 6 and each connec
REFERENCES:
patent: 2282085 (1942-05-01), Nichols et al.
patent: 4120081 (1978-10-01), Rosch et al.
patent: 4776075 (1988-10-01), Kawabata et al.
patent: 4907545 (1990-03-01), Mills
patent: 5771776 (1998-06-01), Itoh
JP 3-145554A., In Patents Abstracts of Japan M-1158, Sep. 13, 1991, vol. 15, No. 366.
Bing Karlheinz
Ruhle Martin
Warth Fritz
Wimmer Heinz
Huynh Hai
Mahle GmbH
Yuen Henry C.
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