US2707136A

US2707136A - Insert ring for pistons

Info

Publication number: US2707136A
Application number: US410789A
Authority: US
Inventors: Everett G Fahlman
Original assignee: Permold Co
Current assignee: Permold Co
Priority date: 1954-02-17
Filing date: 1954-02-17
Publication date: 1955-04-26
Anticipated expiration: 1972-04-26

Description

United States Patent INSERT RING FOR PISTONS Everett G. Fahlman, Medina, Ohio, assignor to The gilrmold Company, Medina, Ohio, a corporation of Application February 17, 1954, Serial No. 410,789

3 Claims. (Cl. 309-14) This invention relates to aluminum alloy pistons in which a cast iron reinforcing band is provided in the head of the piston that is grooved to receive the uppermost plston rmg.

In high speed, heavy duty, internal combustion engines the heads of the pistons are subjected to intense heat which softens the metal of an aluminum alloy piston to an extent such that the steel piston ring in the upper groove of the piston head tends to gradually widen its groove by a hammering action on the side walls of the groove, thereby reducing the effectiveness of the seal and shortening the life of the piston. To eliminate this difiiculty, aluminum alloy pistons have sometimes been provided with a carrier band of iron embedded in the piston head and grooved to receive a piston ring. Such carrier bands being of greater strength and being more heat resistant that the aluminum of the piston body, are able to withstand the hammering action of the piston ring, but there are certain difficulties incident to the manufacture and use of such carrier bands. The casting of the piston with the iron band embedded in the body of the piston presents certain difliculties and the fact that the ferrous alloy of the carrier band is a poorer conductor of heat than the aluminum piston body, tends to impede the transfer of heat from the piston head to the cylinder wall and increase the temperature to which the piston head is heated in service.

When a carrier ring is employed which has a coefficient of expansion materially different from that of the aluminum alloy forming the body of the piston, severe stresses tending to distort the piston and the carrier band and to weaken the bond between the band and the piston body are set up in the piston in the process of casting the same, with the result that subsequent heating and cooling of the piston causes deterioration of the bond. Iron alloys having a relatively high coefficient of expansion and having the requisite strength of heat resisting bodies when cast are commercially available and it is possible to obtain such an iron alloy that has a coefficient of expansion substantially the same as that of the high silicon aluminum alloys commonly used in making cast aluminum pistons. The use of cast iron bands of such iron alloys eliminates the difficulties due to unequal rates of expansion, but the problem of permanently fixing the embedded iron carrier band to the aluminum body of the piston and the problem of minimizing the heat blocking effect of the iron carrier band still remains.

The iron carrier band can be firmly anchored in the piston head and a good heat conducting connection between the piston body and the carrier ring can be obtained by providing an integral aluminum iron alloy bond between the aluminum of the piston and the embedded carrier band. Such a bond has heretofore been provided by first suspending the carrier band in molten aluminum for a length of time sufiicient to enable the aluminum to alloy itself to the band by'means of a thin layer of aluminum iron alloy and then casting the piston about the band while the aluminum coating is still in a fluid state. This method, however, adds very materially to the cost of manufacturing a piston.

The present invention provides a piston in which a mechanical bond of adequate strength is provided between the piston ring carrier band and the metal of the piston head and in which superior heat conduction is provided from the face portion of the head through the carrier band to the piston ring.

In addition, the present invention provides a construc- 2,707,136 Patented Apr. 26, 1955 tion which closely spaced inspection openings are provided 1n the carrier ring throughout its circumference and in WhlCh the ring is so constructed that it is not materially weakened by the openings. Portions of the carrier ring that are enveloped by the aluminum of the piston are so formed that a relatively large surface area of the carrier band contacts with portions of the piston that are heated in service to the highest temperatures so as to provide for a more rapid transfer of heat from the aluminum piston body to the carrier ring. The carrier ring is also formed with anchoring projections and recesses that are so shaped that they offer a minimum resistance to flow of the aluminum alloy in the mold during solidification so that close contact of the aluminum with the carrier band is obtained and initial stresses in the cast aluminum piston body due to the presence of the iron ring are reduced to a minimum.

The carrier band of the present invention is formed of an austenitic cast iron containing a relatively high percentage of nickel. The coefficient of expansion of such alloys can be varied by increasing or decreasing the nickel content and may be made to correspond very closely to the coefficient of expansion of the particular aluminum alloy used in the piston. These iron nickel alloys also have good heat resistant properties, dovnot grow appreciably after repeated heating and cooling, and are resistant to oxidation even at the casting temperature of aluminum. An example of an iron alloy having the properties above referred to is an alloy containing 14% to 20% of nickel, about 5% of copper and 1% to 4% of chromium.

Objects of the present invention are to provide an aluminum alloy piston having an iron piston ring carrier band that is joined to the metal of the piston by a firm mechanical bond which resists relative circumferential, axial and radial movements of the band with respect to the piston body, to provide a piston in which the band is so formed that the molten aluminum alloy can flow freely past and around the band and the mold and remain in close contact therewith throughout the surfaces of the band that are embedded in the piston after the casting is cooled, to provide a piston in which the band is so formed that it has a large surface area contacting with the metal of the piston head on the side thereof facing the piston head face, and to provide effective conduction of heat from the piston head to the band.

A further object of the invention is to provide the piston ring carrier band with a large number of inspection openings at the bottom of the piston ring receiving groove and to so dispose said openings with respect to the anchoring ribs that the ring is not materially weakened by the openings.

Reference should be had to the accompanying drawings forming a part of this specification, in which:

Figure 1 is a perspective view of a carrier band in the form which it has prior to being placed in the piston mold;

Fig. 2 is a central vertical section of a piston in which a piston ring carrier band has been embedded and showing (tihe piston ring receiving groove cut in the iron carrier Fig. 3 is a fragmentary horizontal section taken on the line indicated at 3--3 in Fig. 2; and

Fig. 4 is a fragmentary vertical section through the piston wall on an enlarged scale.

In the accompanying drawings the head. portion of an aluminum alloy piston 10 is shown, the piston having a top face 11 that is subjected to heated gases in the combustion chamber of an engine and an iron piston carrier band 12 that is embedded in the head portion of the piston adjacent the face 11. The ring 12 is accurately po sitioned in the piston mold by clamping the peripheral portion thereof between the cope and the drag of the mold. After the piston is cast the periphery of the casting is machined to true cylindrical form so that the periphery of the ring 12 is flush with the periphery of the piston body. The "ring 12 is provided with an annular row of regularly spaced projections 13 that are spaced uniformly from the exterior periphery of the band. Each of the projections 13 is circumferentially elongated and has a longitudinally arcuate top edge 14 that merges at its ends into the top face of the ring 12.

Inwardly of each of the projections 13 and centrally disposed with respect thereto a notch 15 is formed in the ring 12. Each notch 15 is narrower than. the projection within which it is positioned, the width of each notch being preferably less than half the length of the projection. The bottom wall 16 of each notch is flush with the face of the adjacent projection 13 and the lower end wall 17 of each notch is above the bottom face of the band and preferably near the median plane of the band, The band 12 has top and

bottom faces

18 and 19 that taper toward the outer periphery of the band. The outer portions of these faces are preferably machined to provide an accurate fit with ledges on the cope and drag which position the ring in the mold. The top and

bottom corners

20 and 21 of the ring at the interior periphery of the ring are rounded to lessen resistance to the flow of molten metal in the mold and to avoid the creation of internal stresses in the casting in cooling. The projections 13 have transversely rounded longitudinal edges 22 and the notches 15 have rounded edges 23 that permit the molten metal to flow more freely around the projections and into the notches during casting and to maintain close contact with the surfaces of the bond during solidification so that internal stresses due to the solidification of the aluminum around the iron band are minimized.

A piston ring groove 24 is cut in the band 12 after the piston has been cast and this groove is preferably of a depth to intersect the notches 15 and to form an opening 25 to each of the notches which will permit visual inspection of the bond between the aluminum and the iron band at closely spaced points throughout the circumference of the band.

The projections 13 and the entire interior of the carrier band have rough surfaces that are formed in casting the band and these surfaces strengthen the mechanical bond between the aluminum of the piston body and the carrier band. By providing the projections 13 and the notches 15 opening to the top face of the carrier band, a large area of contact is provided between the carrier band and the portion of the piston head above the carrier band and, since the top portion of the piston head is heated to a higher temperature than other portions of the piston, the larger area of contact with the more highly heated portions of the piston offsets to a great extent the heat blocking effect of the carrier due to its lower heat conductivity.

It is to be understood that in accordance with the pro visions of the patent statutes, variations and modifications of the specific devices herein shown and described may be made without departing from the spirit of the invention.

What I claim is:

1. A cast aluminum alloy piston having a cast metal reinforcing band embedded in the head portion thereof, said band being composed of a ferrous alloy having a coeflicient of expansion approximately the same as that of the aluminum alloy of the piston and being positioned in said head with its exterior periphery at the piston periphery and with the remainder thereof enveloped by the metal of the piston, said band having an annular row of circumferentially elongated projections on its top face that are in a zone intermediate the interior and exterior margins of said top face and spaced inwardly from the piston periphery, said projections being spaced circumferentially and having longitudinal edges of arcuate form, said band having a notch extending downwardly from its top face inwardly of each of said projections and terminating above the bottom face of said band, said band being embedded in the piston with said projections extending toward the piston head face and with the metal of the piston filling said notches, said piston having a circumferential piston ring receiving groove cut in said band to a depth to extend into said notches and into the metal of the piston body in said notches, said groove forming spaced openings in said band that are bridged by said projections.

2. A cast aluminum alloy piston having a cast metal reinforcing band embedded in the head portion thereof, said band being composed of a ferrous alloy having a coefficient of expansion approximately the same as that of the aluminum alloy of the piston and being positioned in said head with its exterior periphery at the piston periphery and with the remainder thereof enveloped by the metal of the piston, said band having an annular row of circumferentially elongated projections on its top face that are in a zone intermediate the interior and exterior margins of said top face and spaced inwardly from the piston periphery, said projections being spaced circumferentially and having longitudinal edges of arcuate form, said band having a notch extending downwardly from its top face inwardly of each of said projections and terminating above the bottom face of said band, said band being embedded in the piston with said projections extending toward the piston head face and with the metal of the piston filling said notches, the notched interior of said ring and said projections having rough surfaces, the edges of said notches being rounded and the arcuate edges of said projections being transversely rounded, said piston having a piston ring receiving groove cut in said band to a depth to intersect said notches.

3. A cast aluminum alloy piston having a cast metal reinforcing band embedded in the head portion thereof, said band being composed of a ferrous alloy having a coefficient of expansion approximately the same as that of the aluminum alloy of the piston and being positioned in said head with its exterior periphery at the piston periphery and with the remainder thereof enveloped by the metal of the piston, said band having an annular row of circumferentially elongated projections on its top face that are in a zone intermediate the interior and exterior margins of said top face and spaced inwardly from the piston periphery, said projections having longitudinal edges of arcuate form that merge into said top face at. their ends, said projections being of uniform size and regularly spaced, said band having a notch extending downwardly from its top face inwardly of each projection and terminating above the bottom face of the band, each notch being disposed centrally of a projection with its bottom flush with an inner face of the projection, said band being embedded in the piston with said projections extending toward the piston head face and with the metal of the piston filling said notches, said piston having a circumferential piston ring receiving groove cut in said band to a depth to intersect said notches and extend into the metal of the piston body in said notches, said groove providing spaced inspection openings in said band that are bridged by said projections.

References Cited in the file of this patent UNITED STATES PATENTS 1,979,335 Mahle Nov. 6, 1934 2,124,360 Welty July 19, 1938 2,255,006 Graham Sept. 2, 1941 OTHER REFERENCES Automotive Industries, Vol. 105, Issue No. 9, Nov. 1, 1951. Inside of back cover.