US 3152523 A
Description (OCR text may contain errors)
13, 1964 M. cs. WHITFIELD ETAL 3,152,523
PISTON FDR INTERNAL COMBUSTION ENGINES Filed Aug. 16, 1962 2 Sheets-Sheet l BY Ham-3 Wesldke A6EN7' Z0 INVENTORS Mars\na1l G WhLH'LelcL- Oct. 13, 1964 M. a. WHITFIELD ETAL 3,152,523
PISTON FOR INTERNAL COMBUSTION mamas Filed Aug. 16, 1962 2 Sheets-Sheet 2 INYENTORS United States Patent 3,152,523 PISTON FOR INTERNAL COMBUSTION ENGINES Marshall G. Whitfield, hrookfield, Conn. Whitfield Laboratories, Inc., R0. Box 293, Bethe Conn.), and Henry Weslalre, Harbour Road, Rye Harbour, Sussex, England Filed Aug. 16, 1962, Ser. No. 217,416 3 Claims. (Cl. 92-213) This invention relates to pistons for internal combustion engines, and more particularly to pistons for use with engines of the type employing fuel injection.
In internal combustion engines of this type, pistons which were made entirely of light metal such as aluminum or aluminum alloy, have not proved to be satisfactory, due in large part to the erosion caused by the fuel injection into the cylinders. In some instances the light metal of the piston was actually melted, particularly where the hottest area existed at the top or head, resulting in early failure.
In the past various proposals have been made to remedy this problem, such proposals involving the use of head caps, inserts or facings of a harder material or metal, intended to withstand the high temperatures. In the case of inserts, these were located in the path of the injected fuel, to bear the brunt of the impingement thereof on the piston head.
While the above arrangements were of some service, they have not been fully satisfactory to the extent of meeting all of the requirements for this particular use. The construction Where the entire top of the piston was covered with a ferrous metal body or cap proved disappointing primarily because of loosening and separation of the top portion, although excessive heat transmission to other areas also resulted in a distinct disadvantage. Accor ingly, for the most part, pistons which were made entirely of iron have generally been employed in this type of internal combustion engine.
The matter of heat transmission above mentioned constit-uted an important further drawback of these prior constructions, because appreciable amounts of heat were conducted from the piston head or cap to the cylinder block, the lubricating oil, and the associated piston parts.
The above drawbacks and disadvantages of prior piston constructions intended for this purpose have been obviated by the present invention, and one object of the invention is to provide a novel and improved multi-part or multielement piston for the indicated and similar uses, which results not only in a lighter construction but also a greatly prolonged service life together with an appreciable reduction in heat transfer from the combustion area.
A further object of the invention is to provide an improved multi-pa-rt or multi-element piston construction as above set forth, which results in lower oil temperatures, lower bearing loads and temperatures, and in a simplified pin-bearing structure.
An additional object of the invention is to provide a novel piston construction as characterized for the above and similar uses, wherein a rugged heat-insulating metal as titanium or its alloys is combined with a light metal in such fashion as to attain the above objects and at the same time prevent failure from loosening and separation of the constituent parts, which condition has hitherto adversely affected service life.
These and other objects of the invention, which will be set forth hereinafter or will be apparent to one skilled in the art upon reading these specifications, are accomplished in that structure and arrangement of parts, of which certain exemplary embodiments will hereinafter be described. Reference is made to the accompanying drawings wherein:
FIG. 1 is a plan view of a piston from the head end with a part in section, the section being taken transversely at a position just above the pin boss.
FIG. 2 is a side elevation of the piston with certain parts in section.
FIG. 3 is a vertical sectional view of the piston taken along the section line 1-1 of FIG. 2.
FIG. 4 is an elevational view of a modified form of piston with parts in section.
FIG. 5 is a partial elevational view of a piston somewhat modified from the showing of FIG. 4.
FIG. 6 is a top plan view of a composite piston structure, constituting another embodiment of the invention.
FIG. 7 is a fragmentary sectional view of the composite piston structure of FIG. 6, taken on the line 77 thereof.
FIG. 8 is a fragmentary axial sectional view of a composite piston, illustrating a ring groove reinforcement as provided by the invention.
In the specifications which follow, the term titanium will be used to designate portions formed of titanium and its alloys. These portions are prefabricated structures, which may be made by casting, forging or the like, and which are located in molds for the casting of the light metal against them. The term light metal is used herein to designate aluminum and aluminum alloys.
Briefly, in the practice of the invention, a heat-insulating, abrasion and heat resistant head or ring section of titanium metal is provided, which head has portions extending downwardly along the cylindrical side walls of the piston to a point well above the pin bosses, but of sufiicient depth to encompass at least the upper one of the piston ring grooves. The depending portion of the titanium metal head is divided circumferentially by grooved or other configurations into a plurality of parts between which the light metal may flow upon casting. The head has an upper surface shaped as desired but usually concave in configuration to coact with the fuel injection jet. The top portion of the head or ca-p may be relatively thin. In a prefenred embodiment it is provided with downwardly extending bosses, the shape and purpose of which will hereinafter be described.
After suitable treatments hereinafter described, the head or ring element will be placed in a suitable mold and the light metal cast against it to form the remainder of the piston structure. The molding may be done in sand molds or in permanent molds, as desired. The head may be provided with one or more extensions for the purpose of locating it accurately in the mold, and these extensions will be removed when the piston is finished. The finishing is done conventionally by surfacing the cylindrical side walls of the piston including the heavy metal and light metal portions, in a turning operation, accompanied by the milling of the piston ring grooves.
Referring now to FIGS. 1, 2 and 3, there is shown as provided by the invention a piston having a head portion or cap 2 of heat-insulating and heat-resistant titanium metal or alloy. This head has a central top portion 3 of suitable configuration and a relatively heavier rim portion 4 having a depending part 5 of substantially the same thickness. The depending portion of the head is in this instance divided into a plurality of portions 6 by a series of radially disposed slots 7, as illustrated.
The head or ring section is placed in a suitable mold and the light metal is cast against it. It is advisable to make provision for a suitable bond between the light metal of the body and the titanium metal of the head cap or ring section. In one procedure, the cleaned head is electrically coated with tin to a thickness of about .0002 in., more or less. In the casting operation the mold is so constructed and the pouring is accomplished in such a way that the molten metal flows past the surfaces of the ferrous metal body against which it is cast for a substantial interval, carrying away oxides and impurities. In this procedure a sound bond is produced with a minimum of interface alloy, and in many instances no visible interface alloy. In another procedure, the titanium head or ring section may be directly dip coated in a molten aluminum bath unti it is wetted with aluminum, than transferred to a mold wherein additional aluminum or alloy are cast to make the casting. Or, a bonding procedure may be employed as set forth in U.S. Patent No. 2,785,451, which involves titanium and aluminum.
The precise shape and dimensions of the piston form no limitation on the invention, as will be understood, and may be varied in accordance with different designs for different services. The light metal will underlie the central portion of the head, as shown at 15. It will also lie inwardly of the depending portions of the head, as at 16, being thick enough to impart sufficient strength and rigidity to the upper part of the piston. The piston will normally have a skirt portion 17 which is relatively thinner and may be as long as required by the particular design. The piston will be characterized by openings 18 in which the wrist pin is engaged, these being provided with the inwardly exxtending wrist pin boss 12. It is usual in the design of many pistons to connect the wrist pin bosses with the upper part of the piston by relatively thickened portions or wrist pin ribs 19 which may have a variety of shapes.
In casting the light metal against the head or ring section, i.e. between the head, outer mold walls, and a suitable core element or elements, the molten light metal will coat the entire interior portion of the head, and be bonded thereto, and will flow into the interstices 7 between the downwardly projecting elements of the head. An interlocked design is thus produced in addition to the bonding aforesaid.
A modified form of structure is shown in FIG. 4 in which like parts have been given like index numerals. Here the downwardly projecting portion of the head has been divided into spaced extensions 20 which are preferably so shaped as to provide downwardly converging portions 21 terminating in end enlargements 22. This not only minimizes weight for a given downward extension of the head, but also provides an anchoring structure, as will be evident.
Additionally, it is preferred to provide the central head portion 3 with downward extensions 23, of which three have been shown in FIG. 4, although more may be provided as will readily be understood. In a symmetrical construction in accordance with the design of FIG. 4, there would be five such downward extensions. The downward extensions preferably comprise head portions connected to the top of the piston head by necks of relatively smaller cross sectional dimensions, and are roughly mushroom shaped. This provides a structure in which thermal stresses in one direction are offset by thermal stresses in the opposite direction, whether under the particular thermal conditions the light metal or the heavy metal is expanding more rapidly. The reduction in area also relieves stress on the bond. The cap remains tight at all times during the operation of the engine.
In the structure of FIG. 4, the upper piston ring groove 24 is formed entirely in the downward projection of the head. The groove 25 in this instance is formed partly in the downward head extensions Zti and partly in the light metal body of the piston. In PEG. there is shown a modification in which the spaces between the extensions 20 are carried upwardly so as to cut the upper piston ring groove 24-. The anchoring action is the same, but a still further saving in Weight is effected.
Another embodiment of the invention is illustrated in FIGS. 6 and 7, wherein the head cap and ring section 26 has a diiferent, particular configuration providing a head cavity 27 found to be desirable for utilizing to the fullest extent the fuel injection characteristic of certain combustion engines. As shown in this figure, the head cavity 27 is circular or cylindrical, and nonconcentrically disposed in the cap, the eccentricity being evident from the spaced centers 28 and 29 of the cavity and cap respectively. By such eccentricity the cavity may be located at the most advantageous point with respect to the injected fuel, to receive and distribute the latter. Further, the cap is provided with angularly extending tangential holes or passages 30 in the manner shown in the section of FIG. 7. These holes are of number, angle and diameter to suit the particular head cavity in use. Upon compression in the engine, the rapid air movement through these passages causes a violet rotational movement or swirling of the air in the cavity 27, which promotes more complete and faster combustion.
The presence of the passages 30 also tends to oppose localized attack on the piston crown or cap by high temperature gases, owing to the already-mentioned swirling characteristic. During the combustion, the path of the burning gases passes from the cavity to the squish or peripheral areas of the piston via the tangential passages 30. Thus, in conjunction with the titanium metal of the cap 26, the cavitated configuration of the top surface portions thereof enables high engine temperatures to be successfully withstood. The combination is effective and advantageous, in consequence, in accomplishing the objectives of the invention.
Still another embodiment of the invention is illustrated in FIG. 8. In this figure there is shown a piston-ring groove reinforcement inset or insert of titanium in the form of an annulus 32 having an external annular pistonring groove 34, the said inset being joined to a piston body 36 of light weight metal such as aluminum, aluminum alloy or equivalent substance. Preferably, as shown, an interlocking construction is effected between the ring reinforcement or inset 32 and the piston body 36, as by the provision of an internal annular groove 38 in the inset, which groove is occupied by an annular integral portion at of the piston body. By such interlocking construction there is positively prevented any failure of the piston due to loosening or separation of the components, inasmuch as it is physically impossible, except by breakage, to separate the interlocking parts.
The annular reinforcement or inset 32 is, in accordance with the invention, consituted of heat insulating and heatresistant metal, such as titanium or alloys of the same as above mentioned, which have a low heat conductivity and and hi h melting point. Any desired configuration may be provided at the end face 40 of the piston shown in FIG. 8, the flat surface shown being used for simplification of illustration.
From the foregoing it will be seen that we have provided a novel and improved composite piston construction which is especially adopted and advantageous for use with internal combustion engines of the type employing fuel injection. Not only does the composite piston structure successfully withstand the high combustion chamber temperatures and the adverse effects of impingement of the injected fuel, but a marked decrease of heat transmission is effected to the piston body and associated parts of the piston, as well as the side walls of the cylinder, and to the lubricating oil. The composite piston is of relatively simple construction, and may be readily economically fabricated and produced by the procedures outlined.
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. For use in a fuel injection internal-combustion engine, in combination, a heavy titanium metal head structure and a light metal piston body structure carrying the head structure, said head structure comprising a covering portion for the top of the piston body structure, said covering portion having a thickness which at the least is not greatly less than the thinnest side wall portions of the piston body structure and said covering portion being constituted essentially of titanium characterized by heatinsulating qualities which are appreciably greater than the heat-insulating qualities of the piston body structure on which it is carried, said covering portion having a depending peripheral skirt which is greater in wall thickness than the remainder of the covering portion.
2. For use in a fuel injection internal combustion engine, in combination, a heavy titanium metal insert and a light metal piston body structure carrying the insert, said insert comprising a circular structure secured to upper portion of the piston body structure as an insert in surface portions thereof, said insert having a thickness which is greater than the thinnest side wall portions of the piston body structure and said insert being constituted essentially of titanium characterized by heat-insulating qualities which are appreciably greater than the heat-insulating qualities of the piston body structure on which it is carried, said insert band having an axial dimension which is substantially greater than its thickness.
3. For use in a fuel injection internal combustion engine, in combination, a piston comprising a light metal body structure and a titanium head band structure secured to said body structure and extending circumferentially along the cylindrical side walls thereof, said band structure having an exposed edge constituting a portion of the head surface of the piston body structure and being constituted of a heavy metal characterized by heat-insulating qualities and containing essentially titanium, said head band structure having a thickness which is greater than the thinnest side wall portions of the piston body structure and the heat-insulating qualities of said band structure being appreciably greater than the heat-insulating qualities of the piston body structure.
References Cited in the file of this patent UNITED STATES PATENTS