US2771327A - Piston construction - Google Patents

Description

Nov. 20, 1956 w. c. REINBERGER 2,771,327

PISTON CONSTRUCTION Filed Aug. 17, H1953 2 Sheets-Sheet 1 F.4quf

IfiZETLTZ UT' WU 11am CT Fakzbezyez" Nov. 20, 1956 w. c. REINBERGER 2,771,327

PISTON CONSTRUCTION Filed Aug. 17, 1953 2 Sheets-Sheet 2 13w .ELL E 7712:?

William 6'. Febzbezyer ag I i {M W M E If E United States Patent 2,771,327 PISTON CONSTRUCTION William C. Reinberger, Middleburg Heights, Ohio, as-

's'ignor to Thompson Products, Inc., Cleveland, Ohio, a 1 corporation of Ohio Application August 17, 1953, Serial No. 374,747

Claims. (Cl. 309-12) The present invention relates to pistons. -More particular-ly, it relates to skirt control of forged pistons and to themethod of incorporating expansion control rings in an already formed piston.

It is known that aluminum pistons have a coefiicient of expansion roughly twice that of iron or steel from which internal combustion engine cylinders are produced. Accordingly, as the temperature of -an internal combustion engine rises, the aluminum would, if not controlled, expand to the point of binding within the cylinder. Hitherto, expansion control has been restricted to cast pistons that have control rings embedded thereon or to pistons having a complicated interlacing of the control rings therein. The present invention now provides a forged piston having a control ring press-fitted therein.

In producing cast pistons with metal control bands contained in the top of the skirt portion, it is customary to make the piston so that the top of the skirt portion is cam-ground or oval-ground. By cam-ground or ovalground is meant that the top of the skirt portion of the piston isground into a cam-like or oval-shape. The thrust faces which are normal to the wrist .pin axis of the piston lie on the major diameter of the oval, with only said thrust faces making contact with the cylinder wall when the piston is cold. The wrist pin boss faces of the piston when cold do not contact the cylinder walls, but rather, are spaced therefrom a minute distance.

As a cast, cam-ground, control band-containing-aluminum piston is subjected to elevated temperatures, such as are encountered during the operation of an internalcombustion engine, the head, and top of the skirt portion of said cylinder tend to expand. Since the head portion and wrist pin 'boss portions contain larger masses of metal than the skirt portion, and because the head portion is directly in contact with the extremely high temperatures of the burning fuel, said head portion and wrist pin boss portions necessarily tend to expand at a more rapid rate than does the skirt portion. Accordingly, as the wrist pin boss portions expand, their expansion tends to pull the thrust faces of the oval piston toward the center of the piston. This pulling in of the thrust faces tends to cause the top of the skirt portion to assume a more circular configuration. The metallic control band incorporated in the top of the skirt portion of the piston aids this pulling in of the'thrust faces in the following manner:

The expanding, outwardly moving wrist pin b'o'ss portions exert a stretching effect upon the band, causing said band to be slightly deformed in a somewhat oval configuration. Since the control band is completely encased within the metal in the top of the skirt portion during the casting operation,-the deformation of the control band by thee'xpanding wrist pin boss portions causes the band to bear inwardly on the thrust face portions, thereby exerting an increased inward force on said thrust faces. In this manner, the piston at high temperatures is transformed from its originally oval shape to a circular, smooth fitting relationship to the cylinder walls. The uses-of a metal control band in cast pistonsto control expansion is commonly called hoop-stretching of the upper portion of the piston skirt.

Pistons which are produced by forging, and not casting, have been found to be superior to cast pistons in several ways. They are not only as wear-resistant as cast pistons, but further, have greater ductility and strength than their cast counter parts. Also, forged pistons can be produced much more rapidly and economically than can cast pistons. To date, however, forged pistons have not been feasible for use in internal combustion engines because it was not possible to incorporate a metal control band in the piston in order to compensate for the differences in the coefiicient of thermal expansion existing between the forged aluminum piston and the iron or steel cylinder wall. This invention, however, now renders it possible to insert an expansion control ring into a forged piston without actually casting the ring into the piston as was heretofore necessary.

According to my invention, a cold shrunk control band or ring is press fitted into a heat expanded forged piston. In this manner, it is possible to duplicate the conditions existing in a cast piston containing a control band so as to have a forged piston having all the desirable expansioncontrol properties of the prior cast pistons, but with the added advantages and properties of greater ductility and greater strength of the forgedpiston.

Accordingly, an object of the present invention is to provide a forged piston with a control band incorporated therein to regulate the heat expansion characteristics of the piston.

Another object is to provide a method of incorporating a control band into a forged piston.

Still another object is to provide a ferrous metal ring in an internal groove of a forged aluminum piston to control skirt expansion by imparting a hoop-stretching effect when said piston expands at elevated temperatures.

Other objects and advantages will be apparent to those skilled in the art from the following description of the annexed sheet of drawings which shows a preferred embodiment of this invention:

On the drawings:

Figure l is a longitudinal cross-section of a piston and cylinder assembly showing a forged piston of the present invention, with a ferrous control band contained therein;

Figure 2 is a transverse cross-sectional view of the piston of Figure 1 taken along the line 11-11, showing the piston at the elevated temperatures encountered during operation in an internal combustion engine;

Figure 3 is a longitudinal cross-sectional view of a forging die and punch assembly used in producing the forged piston of the present invention and illustrating the slug or billet from which the .piston is formed;

Figure 4 is a'view similar to Figure 3 but showing the position of the'parts at the end of the forging stroke; and

Figure 5 is a longitudinal sectional view of the forged piston blank of the present invention showing the manner in whicha steel control band is press-fitted into the body of the piston.

As shown in the drawings:

In'Figure l, the forged trunk-type piston 10 of this invention is, slidably mounted within an engine cylinder 11. The piston 1'0 has a headportion .12 with a depending ring 'flange 12a, a skirt 13, and opposed wrist pin bosses 14, 14 depending from the head and ring flange in spaced parallel relation inwardly from the skirt 13. A deep rib R depending from the head portion 12 between the wrist pin bosses 14, 14 and integral therewith forms a connecting bridge between said wrist pinboss s.

The pin bosses 14, 14 have holes 14a therethrough aligned with holes 13a in the :skirt '13. These aligned holes are adapted to receive a,-wrist ping-(not shown),.

3 These pin bosses have arcuate outer faces 14b spaced inwardly from the skirt 13. The ring flange 12a has three rings grooves around the periphery thereof for receiving rings 16 to ride on the cylinder wall 11. Two arcuate lips 18a are provided on the ring flange 12a.

Since the wrist pin bosses 14 are disposed inwardly from the skirt 13, channels 17 are formed between the pin bosses and the skirt. Since the ring flange 12a is thicker than the skirt 13, shoulders 17a are provided at the base of the ring flange and, of course, the channels 17 also terminate at these shoulders. The shoulders 17a thus have lips 18a and the arcnate surfaces 14b of the pin bosses 14 providing abutments on the inner periphery thereof. As shown in Figure 2, these arcuate abutments are spaced 90 apart.

The piston 10 is composed of metal having a relatively high rate of heat expansion such as aluminum or the like. The cylinder 11, on the other hand, is composed of a ferrous metal such as iron or steel having a lower rate of heat expansion.

The head and upper skirt portion of the piston of the present invention are cam-ground. This cam grinding or oval grinding of the piston is done in such a manner that the thrust faces are normal to the wrist pin axis and lie on the major diameter of the oval. Accordingly, when the piston is at normal temperatures, that is, not at the elevated temperatures encountered when the engine is in operation, the thrust faces which are normal to the wrist pin boss axis are in contact with the cylinder wall 11, while the minor diameter of the oval, that is, the piston face in the area of the wrist pin bosses, is separated from the cylinder walls a minute distance.

In accordance with this invention, in order to regulate the fitting of the piston 10 in the cylinder 11 at the operating temperatures of the piston and cylinder by means of a hoop-stretching" effect, there is provided in the piston 10 a. control ring or band 18 of a ferrous metal having substantially the same coeflicient of heat expansion as the cylinder 11.

As the temperature increases in an internal combustion engine, the temperature of the piston 10 is necessarily increased. The head portion 12 which is in direct contact with the burning fuel is heated much more rapidly than is the skirt portion 13. This is due first of all, to the close juxtaposition of the cylinder head 12 and the burning fuel, and secondly, to the greater size and larger mass of metal contained in the head portion 12 as compared to the skirt portion 13. The skirt portion 13 being relatively thin and in close contact with the cylinder wall 11 necessarily dissipates its heat more rapidly, thereby having a lower temperature than the head portion. As the temperature of the head portion increases, the heat is transmitted to the wrist pin boss portions 14 and the deep rib R. The greater amount of heat present in the head portion, wrist pin boss portions and deep n'b R, cause these parts, especially the wrist pins, to expand at a more rapid rate than the skirt portion 13. Accordingly, as the wrist pins 14 and the deep rib R expand, the wrist pins are moved outwardly along the wrist pin axis normal to the thrust faces. Since the ferrous band 18 is tightly contained in the channel 17 between the wrist pin portions and the upper portion of the skirt and against the outer faces 14b of the pin bosses, the outward force of the wrist pins on said ring causes the ring to be slightly deformed into an oval shape. Accordingly, the metal band 18 is pulled in toward the center of the piston along a line normal to the wrist pin axis, thereby forcing or pulling in the thrust faces of the piston. This pulling in, or hoop-stretching eflEect is aided by the lips 18a, 18a which act as an abutment shoulder for the ring or band 18. The lips 18a which are an integral part of the ring flange aid materially in creating this hoop-stretching effect.

The deep rib R is not absolutely necessary in creating the hoop-stretching efiect' It does, however, materially increase the efiiciency of this phenomenon, by enabling the heat to be more rapidly transferred from the head portion 10 to the wrist pin portions 14. Further, the large size and heavy nature of the deep rib R tends to give an added expansive force against the wrist pin portions when the rib R is heated and expands. This increases the stress and resulting hoop-stretching effect on the metal control band 18.

In accordance with this invention, it is not necessary to imbed the control band or ring 18 in the aluminum piston and, therefore, the piston may be forged from a slug or billet as illustrated in Figures 3 and 4. As shown therein, a die block 19 with an ejector bottom 19a provides a die cavity 20 for receiving a cylindrical slug or billet 21 of aluminum or similar lightweight expansible metal or alloy. The punch 22 is suitably mounted for reciprocation, above the die 19, in and out of the die cavity. This punch 22 has a reduced diameter end portion 22a for forming the skirt 13 therearound. A centrally projecting end 22b on the punch forms the interior contour of the piston and the deep rib R. Opposed recesses 220 are provided on opposite sides of the portion 22b to form the pin bosses 14.

In forming the piston 10 in the die assembly of Figures 3 and 4, the slug or billet 21 is heated to forging temperatures of about 750 to 1000 F. The punch is introduced into the die cavity on top of the slug 21 and the metal is forged and extruded around the punch to produce the piston shape 21a from the slug 21 as shown in Figure 4. The punch is then removed and the ejecter bottom 19a of the die 19 is actuated to push the forged piston out of the die cavity 20.

After the forging operation, and while the forge blank 21a is still at elevated forging temperatures and preferably not lower than about 900 F., the conttrol band or ring 18 is press-fitted into the heated blank 21a. The ring is preferably shrunk at a low temperature as by means of Dry Ice or other coolant to reduce its dimension as much as practical. On the other hand, the piston is heat expanded at a temperature of about that which is reached in normal operation. The ring 18 is inserted in the skirt of the blank 21a and is forced by a press-fitting tool 23 into the piston to be bottomed on the shoulders 17a. As shown in Figure 5, the tool 23 has a cylindrical end portion 231: with a recessed end face 23b for fitting over the top end of the ring 18. The tool 23 is forced into the piston to drive the ring 18 through the channels 17 into a firm seat on the shoulders 17a. As the aluminum of the piston blank 21a cools, and the band 18 becomes heated, the aluminum contracts and the ring expands. Since the coefficient of thermal expansion of aluminum is greater than that of the steel band 18, the contracting aluminum creates an inward force on the band 18. Accordingly, when normal temperatures have been reached, the band 18 exerts a considerable outward pressure or force on the aluminum, especially in the region of the top of the skirt portion which tends to hold the skirt out as much as possible at room temperature.

When the piston is in operation in an internal combustion engine, however, as the temperature increases, the aluminum will expand at a much more rapid rate than will the steel band 18. Accordingly, the outward pressure of the band and the inward pressure of the aluminum will eventually reach a state wherein the compressive forces are approximately zero. Accordingly, as the outward force of the steel ring decreases with temperature increase, the corresponding outward expansion of the wrist band portions due to expansion of said wrist pins and the deep rib R cause the steel ring to pull inwardly along the thrust faces, thereby forcing the previously oval-shaped upper skirt portion into a circular configuration, thus assuring a good smooth running fit of the piston 10 within the cylinder 11.

From the above description it will be understood that 5 this invention now. provides a forged piston having a control band force fittedth'er'ein. The invention makes p'ossibleithe production of band-controlled forged pistons since the control bands need not be imbedded in the piston metal to perform their control functions.

.-It will be .Iappreciated that various modifications and variations may be eflected without departing from the novel scope of the present invention.

I claim as my invention:

1. An expansible trunk type piston composed of metal having a high rate of heat expansion which comprises a head portion, a depending ring flange portion integral with said head portion, a skirt portion thinner than the ring flange portion extending intgrally therefrom, and wrist pin bosses depending integrally from said head portion inwardly of said skirt and coacting therewith to form channels between said bosses and said skirt said piston having an internal shoulder between the ring flange and the skirt portions in communication with said channels, and a ferrous metal control ring having a lower rate of heat expansion than the piston material bottomed on said shoulder, said control ring controlling the expansion of the piston under varying temperature conditions.

2. A trunk type aluminum piston which comprises a head portion, a depending ring flange portion integral with said head portion, a thinner skirt portion extending from the ring flange portion and merged integrally therewith at a shoulder extending transversely to the axis of the piston, wrist pin bosses depending integrally from said head portion and ring flange in spaced relation inwardly from the skirt and coacting with said skirt defin ing arcuate channels therebetween in communication with said shoulder, said skirt and pin bosses having aligned apertures therethrough accommodating a wrist pin, a steel ring bottomed on said shoulder, and said ring controlling expansion of the skirt without interfering with the wrist pin bosses.

3. A trunk type piston of expansible light-weight metal which comprises a head portion having a depending ring flange and a thinner depending skirt integral with said head portion, opposed wrist pin bosses depending integrally from said head portion in spaced relation inwardly from said skirt, said pin bosses and said skirt having a channel therebetween, an internal shoulder in said piston communicating with said channels, aligned openings in said skirt and pin bossesaccommodating a wrist pin, and a metal annulus of low heat expansion metal bottomed on said shoulder and acting on said skirt at elevated temperatures to maintain control of expansion of said skirt at operating temperatures.

4. A trunk type aluminum piston which comprises a head portion, a depending ring flange portion integral with said head portion, a thinner skirt portion extending from the ring flange portion and merged integrally therewith at a shoulder extending transversely to the longitudinal axis of the piston, wrist pin bosses depending integrally from said head portion and ring flange into said skirt in spaced relation inwardly from the skirt, said skirt and pin bosses having aligned apertures therethrough accommodating a wrist pin, a depending deep rib portion extending from an integral with said head portion, said deep rib extending along the axis of the wrist pin bosses and merged with said wrist pin bosses, depending ring abutment lip portions extending from and integral with said ring flange portions, said lip portions being in parallel opposed spaced relation and normal to said wrist pin boss axis, a steel ring bottomed on said shoulder, said ring controlling expansion of the skirt by a hoop-stretching efli'ect.

5. A trunk type aluminum piston comprising a head portion, a depending ring flange portion integral with said head portion, a skirt portion extending integrally from the ring flange and merged therewith at a shoulder extending transversely to the axis of the piston, wrist pin bosses depending integrally from said head portion inwardly from the skirt portion and coacting with said skirt to define arcuate channels therebetween and in communication 'withsaid shoulder, a deep rib portion extending from the head portion along the wrist pin axis and merged with said wrist pin bosses, depending ring abutment lip portions integral with said ring-flange normal to said wrist pi-n axis, and-a'steel annulus bottomed on said shoulder and exerting expansion control of the piston under varying temperature conditions.

6. A trunk type forged aluminum piston which comprises a piston head having both a depending skirt and wrist pin bosses formed integrally therewith, said wrist pin bosses being inwardly spaced from said skirt, a depending deep rib portion integral with said head and wrist pin bosses, said rib extending along the wrist pin axis, depending parallel opposed spaced control ring abutment lip portions integral with said head portion and normal to said wrist pin axis, a steel expansion control ring disposed between said wrist pin bosses and said skirt and exerting an expansion force on the skirt when cooled to a temperature materially less than the operating temperature of the piston, and exerting skirt expansion control by hoop-stretching said skirt at the operating temperatures of the piston.

7. A trunk type piston comprising a head portion, a skirt portion integral with said head portion, opposed wrist pin bosses depending integrally from the head por tion in spaced relation inwardly from the skirt portion, and an expansion control ring in said piston fitted tightly around said pin bosses.

8. A trunk type piston composed of metal having high thermal expansion properties and including a head portion, a skirt portion integral with said head portion, and opposed wrist pin bosses depending from the head portion in spaced relation inwardly from the skirt portion, said wrist pin bosses having arcuate outer faces, and an expansion control ring composed of metal having greater thermal expansion properties than said piston metal fitted in said piston tightly around said arcuate outer surfaces of said pin bosses.

9. A trunk type piston of expansible metal which comprises a head portion having a depending ring flange and a thinner depending skirt form-ed integrally with said head portion, opposed wrist pin bosses depending integrally from said head portion in spaced relation inwardly from said skirt portion, an internal shoulder in said piston between the ring flange and skirt and surrounding said pin bosses, and a metal ring of low heat expansion metal bottomed on said shoulder and tightly fitted around said pin bosses.

10. A trunk-type piston comprising a head portion, a depending ring flange portion and a skirt portion integral with said head portion, and diametrically opposed wrist pin bosses depending integrally from the head portion inwardly of the skirt portion and coacting with the skirt portion to provide arcuate channels between said bosses and said skirt portion, an integral shoulder between the ring flange and the ring skirt portion extending behind said pin bosses and in communication with said channels, and a metal ring having a lower rate of heat expansion than the piston disposed against said shoulder and extending behind said pin bosses, said ring exerting an outward pressure on said skirt to tension the skirt material and to effect a hoop-stretching effect of the piston under increased temperature conditions.

References Cited in the file of this patent UNITED STATES PATENTS 1,418,719 Knight June 6, 1922 1,750,429 Pope Mar. 11, 1930 1,784,291 Jardine Dec. 9, 1930 (Other references on following page) 7 UNITED STATES PATENTS Hartog- Mar. 3, 1931 Greve Dec; 8, 1931 Handler Nov. 28, 1933, Frank Dec. 12, 1933 Teetor Dec. 25, 1934 Debelack Jan. 12, 1937 a a a H I FOREIGN PATENTS 7 Great Britain Mar. '26, 1925 Great Britain 1 Sept. 10, 1948 Germany Dec. '20, 1932- Frarlce May 15, 1935

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