US3084005A - Composite aluminum alloy engine cylinder - Google Patents

Description

April 2, 1963 M. G. WHITFIELD EIAL 3,08

COMPOSITE ALUMINUM ALLOY ENGINE CYLINDER Filed June 23, 1958 INVENTORS. News/MAL GI MIT/FIELD fl EIYJELL CC'mn/Efi ATTORN EYS.

United States Patent 3,084,005 CUMPOSITE ALUMINUM ALLOY ENGINE CYLINDER Marshall G. Whitfield, Garden City, N.Y., and Wendell C. Cheney, Lake City, Minn.; said Wendell C. Cheney assignor, by mesne assignments, to Gould-National Batteries, Inc, St. Paul, Minn., a corporation of Delaware Filed June 23, 1958, Ser. No. 743,659 Claims. (Cl. 309--2) The invention has to do with the provision of cylinders, particularly those for relatively small internal combustion engines. It has hitherto been understood that by reason of the enhanced heat conductivity of light metals such as aluminum it would be advantageous to use such metals in considerable mass in connection with the cylinders. Thus, particularly in air cooled engines, it has been found possible to provide a cylinder lining of cast iron, sheet steel or other forms of ferrous metal, and to cast aluminum around the outside of it in a mass which covers the cylinder lining and provides, for example, cooling fins.

It will be understood that such structures are not only relatively expensive, but involve the provision of a bond between the external structure of light metal and the ferrous cylinder lining. A bond is required not alone for mechanical reasons but to facilitate heat trans-fer from the ferrous lining to the external light metal body. Further, the presence of the ferrous lining interferes to some extent with heat dissipation.

Attempts to manufacture engine cylinders from light metals alone have been made, but have given only a slight degree of satisfaction. The cylinders do not wear well, even where their interior surfaces are chromium plated, or otherwise treated to make them more wear resistant. The light metals and their alloys are not well adapted to withstand the thermal and physical stresses of engine cylinder usage, and the number of failures has been too high.

It is an object of the invention to provide an engine cylinder which is formed from light metals and light metal alloys but which does not present the disadvantages set forth above.

In one aspect, it is an object of the invention to provide a light metal engine cylinder in which the heat transfer is excellent, but which does not involve bonding difficulties.

These and other objects of the invention, which will be set forth hereinafter or will be apparent to the skilled worker in the art upon reading these specifications, are accomplished in that structure and procedure of which certain exemplary embodiments will now be disclosed. Reference is made to the accompanying drawing which shows in section a portion of an exemplary engine cylinder indicating a preferred structure produced in accordance with the present invention.

The term engine cylinder as used herein is employed in the broad sense. While a major utility of light metal cylinders lies in the field of air cooled engines where the cylinder embodies spaced cooling fins, it will 'be understood that the invention is not limited thereto but may "ice be employed in the construction of cylinders utilizing fluid cooling. Further, the term cylinder is not intended to be restricted to a cast structure embodying one cylinder alone, since the invention is applicable to the manufacture of engine blocks containing a plurality of cylinders. The specific embodiment chosen as illustrative is an air cooled engine cylinder, as will be apparent from the drawing, but this is not limiting.

The invention contemplates a light metal engine cylinder, at least the interior surface of which is made from a hypereutectic silicon-aluminum alloy as hereinafter defined.

As silicon is alloyed with aluminum up to about 13%, the silicon can be made to combine with the aluminum, giving a hypoeutectic alloy of substantially homogeneous character. As the amount of silicon increases beyond about 13% of the total weight of the alloy, the alloy takes on a hypereutectic character such that when the molten metal is cooled and frozen some at least of the silicon precipitates in it. When the silicon content increases to about 17% or 18% or greater, the silicon precipitates in massive particles easily discernible under the microscope. These particles increase in size as the silicon content increases.

The silicon particles are very much harder than the alloy matrix in which they are bound; and it has been discovered that a light metal cylinder having an inner surface characterized by massive silicon precipitation is very greatly superior in wear resistance to a cylinder made of light metal but with an interior surface not so characterized. If the quantity of silicon precipitation is sufficient, the 'cylinder will show substantially no scoring even after long periods of use.

The greater the amount of precipitated silicon at the inner or working surface of the cylinder, the greater will be its wear resistance. It is preferred in the practice of' the invention to employ at least at the inner or working surface of the cylinder an aluminum alloy containing at least about 20% of silicon. As the silicon content increases the alloy becomes harder and also somewhat more difficult to machine and finish. The non-uniform character of the surface, i.e. the presence of massive silicon particles in a matrix of softer alloy, results in a machined or finished surface which is characterized by a sub-visual roughness or porosity which is useful in the retention of an oil film for lubricating purposes.

While a satisfactory hypereutectic alloy may be made from commercially pure aluminum with the desired silicon addition, the presence of other alloying ingredients is permissible, providing they are minor in amount and do not affect the essential action of the precipitated silicon. Alloying ingredients which may be employed along with silicon are copper, nickel, magnesium, iron, titanium, manganese, zinc, cobalt and vanadium. Various alloys containing differing amounts of some or all of these substances may be produced, and will serve the purpose of the invention.

Typical alloys which may be used in the practice of the invention are set forth in the following table:

Titanium.. Manganese...

Spec. Gr.--

Table I 21-23 20-22 19-21 23-25 17-19 17-19 21-22 0.9-1.2 1.4-1.8 1.3-1.7 0.8-1.3 4.7-5.3 1.0-1.2 1.01.2 2. 0-2. 4 1. 4-1. 6 05 0. 8-1. 3 3. 8-4. 2 1. 0-1. 2 1. 0-1. 2 -1. 25 0. 4-0. 8 1. 3-1 7 0. 8-1. 3 0. 1-0. 6 1. 1-1. 3 0.5-0.6 70 max. 0. 7 0. 7 0.7 0. 3-0. 4 0. 4-0. 5 0.2 0.2 0.1 .05-0.1 .05-0.1 0. 6-0. 8 0 4-0. 6 0.2 0. 6-0. 8 0.7-0. 8 02 max 0. 2 0. 2 0.2 0. 2 0.5-1.2 0.3-0.5 0.5-0.7 1.0-1.2

Typical physical characteristics for the first of the above alloys are:

Table II As another example, an alloy containing from 20% to 50% silicon, from 1% to 5% nickel, from .5% to 2.5% copper, from 1% to 3% magnesium, up to 1% vanadium and up to 1% antimony, the balance being substantially all aluminum, may be used. Such an alloy is described in United States Patent 2,131,076 to Schwarz.

Complete cylinder structures may be cast from any or all of the alloys indicated above. It is characteristic of high silicon aluminum alloys that they withstand thermal stresses better than pure aluminum; but at the same time they are characterized by a brittleness which increases with the quantity of silicon. As a consequence, where engine cylinders are cast directly from high silicon aluminum alloys there is a limit to the quantity of silicon which may be employed. Various expedients may be adopted to ameliorate this brittleness. It will be usual to subject the alloy castings to a de-growthing heat treatment, such as a treatment at about 500 F. for a period of at least eight hours. Such a heat treatment will normally be effective in dropping the Brinnell hardness of an aluminum alloy containing upwards of silicon from a value of about 150 to a value of about 90. As will be evident from Table I above, such a heat treatment substantially increase the tensile strength of the casting.

The cylinder castings may be made in sand molds or in permanent molds as desired; but a chilling action on the metal at the inner surface of the cylinder may tend to cause the silicon to precipitate in smaller particles.

There are certain materials which, when added in small amounts to the silicon-aluminum alloy serve to break up the silicon masses therein, i.e. to cause the silicon to precipitate in smaller masses which have a more uniform distribution. Among such additives are phosphor copper (copper containing from about .1% to about 2.5 phosphorus) and zinc phosphide. Other materials such as phosphorus pentachloride and sodium and its salts have a similar effect; but are more ditficult to use because of the creation of fumes.

It will be understood further that the effect of brittleness can be ameliorated to a useful degree by so design- 2:; the cylinder structure that a sufficient mass of metal will be present at areas where excessive thermal and physical stresses are likely to be encountered.

Nevertheless, in the casting of solid cylinders of hypereutectic silicon-aluminum alloy, even with control of the various factors outlined above, it is not generally feasible to use more than about of silicon.

Another aspect of the invention, however, presents no such limitation. In this aspect, a sleeve or cylinder lining is formed from a hypereutectic silicon-aluminum alloy, and a body of aluminum or aluminum alloy of different characteristics is cast thereagainst to form the remainder of the body of the cylinder and such fins, bosses and other configurations as may be desired.

The exemplary structure, the formation of which has just been described, is illustrated in the figure where the numeral 1 indicates the preformed sleeve or cylinder of hypereutectic alloy, and the numeral 2 indicates the body or casting of aluminum or aluminum alloy of other character.

The sleeve structure formed from the hypereutectic alloy may contain as much silicon as desired and as is suitable for satisfactory machineability irrespective of whether the alloy itself would be too brittle to permit the casting of the entire cylinder structure of it. The reason for this is that when a body of aluminum or aluminum alloy of different characteristics is cast about the hypereutectic sleeve, the sleeve will be maintained in a condition of compression, while the less brittle chara eristics of the surrounding metal will satisfactorily absorb thermal and physical stresses.

The coefficient of expansion of aluminum is about .000023 per degree centigrade. The coefficient of expansion of a hypereutectic silicon-aluminum alloy containing upwards of about 20% silicon is very much less, being in the neighborhood of about .000016 per degree Centigrade. Thus when aluminum is cast around the outside of a silicon-aluminum alloy and the structure is cooled, the aluminum will be found to be in tension and the hypereutectic sleeve in compression. This situation, although varying in degree, will persist throughout a wide range of temperature below the softening points of the metals. It will be understood further that due to the dissipation of heat by the fins or jackets characteristic of the outer structure, the outer structure is kept below its softening point despite a high rate of heat transfer. The softening point of the inner sleeve will be higher than that of the outer structure.

In the practice of the inventio it is not necessary that the difference between the metal of the inner sleeve and the metal cast about it be as great as that between a hypereutectic alloy containing at least about 20% silicon on the one hand, and commercially pure aluminum on the other. The material of the outer casting may be and preferably is an aluminum alloy containing a lesser quantity of silicon. Thus by way of example aluminum casting alloys known to the trade as A132 and D132 which contain respectively 12% and 9% silicon, balance being substantially all aluminum with normal impurities, may be used and will generally be found preferable to commercially pure aluminum in strength and other characteristics. These are hypoeutectic alloys; but hypereutectic alloys containing above about 13% silicon may also be used. A considerable degree of ductility is desirable in the outer cast structure which will normally dictate a silicon content below about 18%; but it is only necessary to provide an outer structure which will have ductility to withstand the thermal and physical stresses to which the structure may be put to use, and a difference of a few percent in silicon content will usually produce a composite structure characterized by a useful degree of the tensional and compressional forces which have been described. But where an outer cast body is joined to a hypereutectic high silicon sleeve as herein described, the amount of silicon in the sleeve can be carried upwardly within wide limits and in general to as much as 50% if desired.

In making the composite structure of this invention simple cylinders of a hypereutectic aluminum alloy containing preferably more than 21% silicon are cast. The casting may be done in a baked sand mold, and is preferably so accomplished, although permanent molds may be employed. The cylinder or sleeve so cast may then be cleaned in any suitable way as by sand blasting, and may be located in a permanent or other mold to have the body alloy cast against it. In a preferred procedure the high silicon sleeve may be machined to an accurate wall thickness, say A; of an inch, and may then be placed in a die casting machine and an aluminum die casting alloy of lower silicon content may be caused to flow about the present cast cylinder or sleeve and fill the mold to form a complete engine cylinder or block with cooling fins, bosses, flanges, reinforcing webs, or other appropriate structural features.

The melting point of the metal of the sleeve structure will normally be sufiiciently higher than that of the metal cast about it to preclude any melting of the sleeve except at the surface of immediate contact. However, the sleeve may be located in the mold over a mandrel of metal at a lower temperature which will tend to cool the sleeve. No diflicultY is encountered with the formation of a bond since the molten metal tends readily to wet the sleeve. If the sleeve is insufiiciently cleaned or is characterized by oxide on its outer surface, the mold may be so constructed and the pouring so accomplished as to produce a flow-by ettect at the sleeve surface which will carry the oxide away. It has not been found necessary to employ interface coating metals such as tin, zinc or cadmium on the sleeve surface, although the invention would not be avoided thereby.

The cylinder structures of this invention serve very well with light metal or heavy metal pistons having piston rings. They are also adapted for use with pistons not having rings, and in particular in the structures claimed in the copending application of Cheney, Morehouse and Whitfield entitled, Cylinder and Piston Structures, Serial No. 777,036, filed November 28, 1958, now Patent No. 3,021,183.

In the cylinders of this invention the heat transfer through the composite section approaches that of a solid aluminum casting. The hypereutectic sleeve which has been described may be de-growthed or heat treated prior to the casting of the body metal about it or a heat treatment may follow the construction of the entire unit, or both. The use of the separate sleeve as described permits the employment of silicon alloys in the sleeve or liner which are higher in silicon content than any commercial analysis available for ordinary casting work, and higher than any alloys from which non-composite cylinders could satisfactorily be produced.

Modifications may be made in the invention without departing from the spirit of it. The invention having been described in certain exemplary embodiments, what is claimed as new and desired to be secured by Letters Patent is:

1. A light metal cylinder for an internal combustion engine, said cylinder having a unitary body with an inner cylindrical surface for coaction with a piston, said cylinder being made of metal consisting principally of aluminum, the metal at and adjacent said inner cylindrical surface being a hypereutectic silicon-aluminum alloys characterized by precipitation of silicon in massive particles, said alloy containing at least 17% silicon by weight, the remainder of the body of said cylinder containing a lesser quantity of silicon.

2. A unitary light metal cylinder for an internal combustion engine, said cylinder having an inner cylindrical surface for coaction with a piston, the metal of said cylinder adjacent said surface being a hypereutectic siliconaluminum alloy containing substantially 20% to 50% silicon, the remainder of the metal of said cylinder consisting preponderantly of aluminum and containing a lesser quantity of silicon.

3. A light metal cylinder for an internal combustion engine, said cylinder consisting of an inner sleeve presenting an inner cylindrical surface for coaction with a piston, and an outer body in metallic union with said sleeve, said sleeve being made of a silicon-aluminum alloy containing substantially 20% to 50% silicon, and said body being made of a metal consisting preponderantly of aluminum and conatining a lesser amount of silicon.

4. A light metal cylinder for an internal combustion engine, said cylinder comprising an inner sleeve made of a hypereutectic silicon-aluminum alloy, and an outer body in metallic union with said sleeve and made of a hypoeutectic silicon-aluminum alloy.

5. A light metal cylinder for an internal combustion engine, said cylinder comprising an inner sleeve and an outer body in metallic union, said sleeve being made of -a hypereuctic silicon-aluminum alloy characterized by precipitation of silicon in massive particles, said outer body being made of a metal consisting p-reponderantly of aluminum and having a coefiicient of expansion greater than that of the metal of the inner sleeve whereby the inner sleeve in said cylinder is maintained in a state of compression.

6. The structure claimed in claim 5 wherein the metal of said inner sleeve contains substantially 20% to 50% silicon.

7. The structure claimed in claim 5 wherein the metal of said inner sleeve contains substantially 20% to 50% silicon, and wherein said outer body contains less than about 13% silicon.

8. The structure claimed inrclaim 7 wherein the inner sleeve, at least, has the characteristic derived from a heat treatment at about 500 F. for at least about eight hours.

9. The structure claimed in claim 7 wherein the said inner sleeve contains a precipitation controlling agent chosen from a class consisting of phosphor copper and zinc phosphide.

10. An article formed of light metal and having a body with an arcuate surface which in use will have sliding contact with another element, said article being made of metal consisting principally of aluminum, the metal at and adjacent the said arcuate surface being a hypereutectic silicon-aluminum alloy characterized by precipitation of silicon, said alloy containing at least 17% silicon by weight, the remainder of the body of said article containing a lesser quantity of silicon.

References Cited in the file of this patent UNITED STATES PATENTS 1,799,837 Archer Apr. 7, 1931 1,822,877 Archer et al Sept. 15, 1931 1,886,396 Hainlen Nov. 8, 1932 1,940,922 Sterner-Rainer Dec. 26, 1933 2,024,767 Jetiries Dec. 17, 1935 2,106,590 Boegehold et a1. Ian. 25, 1938 2,131,076 Schwarz Sept. 27, 1938 2,277,023 Steiner et a1. Mar. 17, 1942 2,315,558 Somes Apr. 6, 1943 2,320,830 Ricardo et a1. June 1, 1943 2,462,139 Sparkes Feb. 22, 1949 2,656,593 Heintz Oct. 27, 1953 FOREIGN PATENTS 563,616 Great Britain Aug. 23, 1944

Claims (1)

1. A LIGHT METAL CYLINDER FOR AN INTERNAL COMBUSTION ENGINE, SAID CYLINDER HAVING A UNITY BODY WITH AN INNER CYLINDERICAL SURFACE FOR COACTION WITH A PISTON, SAID CYLINDER BEING MADE OF METAL CONSISTING PRINCIPALLY OF ALUMINUM, THE METAL AT AND ADJACENT SAID INNER CYLIN-

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