US1940629A

US1940629A - Piston alloy

Info

Publication number: US1940629A
Application number: US572071A
Authority: US
Inventors: Mahle Ernst
Original assignee: Elektronmetall GmbH
Current assignee: Mahle GmbH
Priority date: 1930-11-01
Filing date: 1931-10-30
Publication date: 1933-12-19
Anticipated expiration: 1950-12-19

Description

E. MAHLE Dec. 19, 1933.

PISTON ALLOY Filed Oct. 3Q, 1931 IN V EN TOR.

MINI] BY W ATTORNEYS.

Patented Dec. 19, 1933 PISTON Ernst Mable, Stuttgart,

Elektronmetall G. m. gart, Germany ALLOY Germany, assignor to b. 11., Cannstatt-Stutt- Application October 30, 1931, Serial No. 572,071, and in Germany November 1, 1930 6 Claims.

During recent years, light metal alloys have come more and more into favour as piston materials, in place of the grey cast iron at one time exclusively used for that purpose. It has,

however, been found that the low hardness of these light-metal alloys at high temperatures constitutes a defect which must be set off against the numerous favourable properties which have substantially contributed to the extended use of said alloys. serious in the This defect becomes extremely piston-ring grooves, inasmuch as the grooves which are exposed to the greatest thermal action, namely near the head, are unable to ofier any prolonged resistance to the impact of the piston rings, but become battered at the prevalent high temperatures, so that the pistons are no longer accurately guided, and, in some events, are even rendered useless. Attempts to improve the high-temperature hardness of the light metals to a substantial extent by incorporating new alloying components, have failed,

It has now been ascertained in accordance with the invention,

that certain beryllium bronzes, which must be classed among the heavy metals, exhibit a quite unusual high-temperature r hardness which seems to render them particularly suitable as structural material for pistons,

at least for the ring portions of same, In such case the actual body made of light metal,

of the piston can still be that portionoi the end,

in which the piston rings are fitted, being rolledin or integrally cast-in an annular shell. However, the entire end of the piston, including the portion carrying the piston rings,

may also consist of beryllium bronze.

As compared with the suggestions for improving the high-temperature hardness of the ring portion by constructing it of grey cast iron and suitably connecting it with the other, lightmetal, portion of the piston, the" construction of the ring portion of beryllium bronze, in accordance with the invention, offers the advantage that the thermal expansion of these alloys approximates far more closely. to that of the light-metal alloys, so

' disadvantages arising that many constructional from the necessity of ob- .sion of the beryllium bronzes,

taining secure connection between the cast iron and light-metal parts of the piston are obviated.

A further advantage over that arrangement consists also in that the heat conductivity of the copper-beryllium alloys is superior to that of grey cast iron, so that the good conductivity constituting one of the main advantages of the light-metal alloys is not impaired, in the present case, to the same extent as when cast iron is used for the ring portion.

In view of the relatively high thermal expanit is advisable, where stress is laid on the noiseless running of the engine, to employ copper-beryllium alloys solely for that portion of the piston that carries the rings, and to make the skirt for which hightemperature hardness and heat conductivity are of minor importance, of grey cast iron or steel plate. In this manner a method or construction is attained in which a head of light metal is surrounded by a beryllium-bronze shell, provided with the piston-ring grooves and carrying a skirt portion of iron, the several structural components being connected together in known manner, but without the previously encountered diffi- 0 culties, since the difierences in the coefficients of thermal expansion of the successive materials merge gradually into one another.

In order more clearly to understand the invention, reference is made to the accompanying drawing which illustrates by way of example, two embodiments of pistons constructed in accordance therewith and in which:

Fig. 1 is a vertical section taken through the gudgeon pin bosses, of one embodiment;

Fig. 2 is a vertical section taken at right angles, to Fig. 1;

Fig. 3 is a plan section along the line A-B of Fig. 1; and

Fig. 4 is a vertical section taken through the gudgeon pin bosses, of a second embodiment.

In both embodiments the piston head 1 is made of light metal, in order to reduce the moving mass, whilst a portion 2, carrying the piston rings and secured shown in Figs. 1 to 3 or by ribs 5, integrally cast with the shell 2 in in Fig. 4. i

In other cases, (such as Diesel engines) where high thermal expansion in the piston skirt is a matter of no importance, the skirt also may consist of beryllium bronze, it being advisable to incorporate a certain amount of manganese in the alloy, in order to increase the resistance to abrasion.

Materials that have been found particularly suitable for the purpose of thgpresent invention, are binary alloys of copper with up to 5 percent (preferably about 2.5 percent) of beryllium, which still exhibit a high-temperature hardness of about 200 Brinell at 350 C. Increased resistance to abrasion, with the same high-temperature hardness, is obtained by the employment of certain alloys of copper with minor quantities of beryllium and manganese, which may be subjected to heat treatment with a 'view of further improving their hardness at lower temperatures. Thus, an alloy containing about 1.5 percent of beryllium and about 3 percent of manganese, the balance being copper, has a hardness of about 200 Brinell at 350 C. in the untreated as Well as the heat-treated form. At ordinary temperatures, however, the hardness of the untreated alloy amounts to only about 150 Brinell, whereas, after a heat treatment comprising heating the alloy to about 750 C. and then quenching, the hardness at ordinary temperatures rises up to about 300 Brinell.

I claim:

1. A piston for internal combustion engines having a ring-bearing portion composed of a beryllium bronze, having copper as its main constituent and containing between about 1 and about 5 percent or beryllium, and having the portion contacting the ring-bearing portion composed of a difierent metal having a coefficient of expansion approximating that of the beryllium bronze.

2. A piston for internal combustion engines having a ring-bearing portion composed of a beryllium bronze, having copper as its main constituent and containing between about 1 and about 5 percent of beryllium, and about 3 perthe embodiment shown cent of manganese, and having the portion contacting the ring-bearing portion composed of a diiTerent metal having a coeihcient of expansion approximating that of the beryllium bronze.

3. A piston for internal combustion engines having a ring-bearing portion composed of a beryllium bronze, the constituents of which are about 1 to about 5 percent of beryllium, about 3 percent of manganese, the remainder being copper, and having the portion contacting the ringbearing portion composed of a different metal having a coeificient of expansion approximating that of the beryllium bronze.

4. A piston for internal combustion engines having a ring-bearing portion composed of a beryllium bronze, the constituents of which are 1.5 percent of beryllium, 3 percent of manganese, and 95.5 percent of copper, and having the portion contacting the ring-bearing portion composed of a different metal having a coefficient of expansion approximating that of the beryllium bronze.

5. A piston for internal combustion engines comprising a piston-head of light metal, an annular shell composed of a beryllium bronze having copper as its major constituent and containing between about 1 and about 5 percent of beryllium and having a coeflicient of expansion approximating that of said light metal surrounding said piston head, grooves adapted to receive piston rings in said annular shell and a skirt portion substantially consisting of iron connected with said annular shell.

6. A piston for internal combustion engines comprising a piston head of light metal, an annular shell, composed of a beryllium bronze, the constituents of which are between about 1 and about 5 percent of beryllium, 3 percent of manganese, and the remainder of copper, and the coemcient of expansion of which approximates that of said light metal, surrounding said piston head, grooves adapted to receive piston rings in said annular shell and a skirt portion substantially consisting of iron connected with said annular sh'ell.

- ERNST MAHLE.