US2003459A - Piston - Google Patents

Description

F. N. NUTT Jung 4, 1935.

PISTON Filed Nov. 25, 1929 m/lZz/f Patented June 1935' UNITED STATES new PISTON Frank N. Nutt, Flint, Mich, assignor, by mesne assignments, to General Motors Corporation,- Detroit, Mich., a corporation of Delaware Application November 25, 1929, Serial No. 409,599

1 Claim.

5 ironor steel, the fact that such light metals and alloys generally have much higher tempera-- ture coeflicients of expansion than cast iron or steel has made it diflicult to produce a piston of such metals or alloys which will fit properly in the cast iron or steel cylinder 'of an internal combustion engine both when the engine is cold and when it is hot. Efforts have been made to overcome this difliculty by incorporating in pistons made of light metals or alloys, struts, rings or other devices made of a metal having a lower temperature coefficient of expansion than the light metal or alloy of which the piston was made to control the expansion of the piston. Pistons of the type described in the preceding sentence have to some extent, but not entirely,

, for the reason, among others, that it has been found practically impossible to bond the metal of which the struts, rings or other devices were made to the light metals or alloys of which the pistons were made so that the former could effectually control the expansion of the pistons, overcome the difliculty mentioned above.

My invention resides in the provision of a pis-' ton which is made entirely of a light metal or alloy, such as aluminum or an alloy of aluminum, which has a, higher temperature coefficient of expansion than cast iron, or steel, and which is so constructed'that it willflt properly in the cast iron or steel cylinder of an internal combustion engine under all operating conditions of the engine. My piston is made of such diameter that it will fit properly in the cylinder of the engine in which itis to be used when the engine is cold. To prevent the piston binding in the cylinder, as the temperature of the engine and the piston increases, due to an increase in the pressure between the cylinder wall and the piston resulting from the difference between the tem perature coefficient of expansion of the material of which the piston is made and that of the material of which the cylinder is made, I construct the piston so as to provide in the cylinder wall bearing surface thereof, a resilient portion which is adapted to be resiliently contracted or collapsed by less pressure of the cylinder walls on the piston than would cause the piston to bind in the cylinder ,so as to reduce the effective size of the piston to less than that which it would assume at the same temperature if it were not resiliently contractible or collapsible, and, fur- 'thermore, so arrange the resiliently contractible or collapsible portion as to hinder the conduction of heat from the head of the piston thereto so as to prevent to a large extent expansion of the portion' and reduce the total expansion of the 5 piston as the temperature of the'engine and the piston increases.

For reasons into which it is unnecessary to go here, it is considered preferable to cast pistons of light metals or alloys, such asalumlnum or alloys of aluminum, in permanent molds, i. e. molds which consist of a body of infrangible material and a core of infrangible material. Thedesign of pistons of light metals and alloys, as made r prior to the time of my invention, rendered it necessary 'to make the core of three or moreparts, which could be separated after the molten metal or alloy of which the piston was made had congealed, so that the core might be removed from the casting. There are several serious ob- 20 jections to the use of multi-part cores. They are difficult and expensive to make; They become warped and distorted and, and consequently, dliilcult to manipulate after a short period of use. And, furthermore, a multi-part core cannot practicably be employed in a pressure casting operation, because the molten metal or alloy would be forced into the fissures between the core parts created by the warping and distortion thereof and would render it practicably impossible to remove the core from the casting. It is an object of my invention to provide a piston of the type described which is so constructed that it may be cast in a mold which consists of a simple two-part body of infrangible material and a sim- 35 ple one-part core of infrangible material.

, For a better understanding of the nature and objects of the present invention, reference is made to the following specification in which there is described the preferred embodiment of 40 my invention which is illustrated in the accomp nying drawing.

In the accompanying drawing: a

Figure 1 is a perspective view of a completed piston in which is embodied my invention;

Figure 2 is a reduced view showing the piston shown in Figure 1 partly in elevation and partly in section on; the line 99 of Figure 3;

Figure 3 is a fragmentary sectional view taken on the line Ill-III of Figure 2; 59

Figure 4 is a sectional view taken on the line ll--ll of Figure 2;

Figure 5 is abottom plan shown in Figures 1 to 4. I

In; the drawing there is shown a one-piece view I of the piston piston which includes a cup-shaped head 20 which is, as usual, of somewhat smaller diameter than the cylinder in which it is to be used and provided with circumferential piston ring grooves 2|. A cylindrical skirt 22, whose external diameter is somewhat greater than that of the head 20, is divided by a pair of diametrically opposed notches 23, which extend thereinto from the upper edge thereof, into relatively thick-walled and thin-walled sides. The walls of. the portions of the skirt below the notches 23 are made thicker than the walls of the sides which they connect in order to give them the necessary mechanical strength. The upper edge of the thick-walled side of the skirt is joined to the lower edge of the side wall of the head, but the thin-walled side of the skirt, into which there extends from the lower edge thereof slot 25, which is, as shown in the drawing, preferably diagonally disposed, is entirely disconnected from the head by a slot 24. Diametrically opposed columns 26, which carry on their lower ends wrist pin bosses 21 which are located within the openings 23 and entirely out of contact with the skirt, are joined at their upper ends tothe head, but are not connected to the skirt except by the webs 28, which extend between the columns and the side of the skirt which is joined to the head, and which serve to conduct heat from the columns to the side of the skirt which is joined to the head and to serve as means for bracing this side of the skirt from the columns.

The piston is made of such diameter that it will flt properly in the clyinder in which it is to be used when the engine is cold and is adapted to be installed in the cylinder so that the heavywalled side of the skirt which is connected to the head and the columns will take the thrust during the power stroke of the piston. When the engine is operated the cylinder walls and the piston become heated and expand. Since the material of which the piston is made expands more rapidly than that of which the cylinder walls are made, the pressure between the cylinder walls and the piston tends to increase as the temperature of the engine rises. The diiference between the rate of expansion of the material of which the piston is made and that of the material of which the cylinder walls are made does not, however,

cause the piston to bind in the cylinder, for before the pressure between the cylinder walls and the piston increases to such an amount as would cause the piston to bind in the cylinder it will resiliently collapse or contract t e thin-walled side of the skirt by. forcing the up r portion thereof radially inwardly and contracting the lower por-.

tion thereof circumferentially by forcing the edges of the slot 25 toward each other. It will. of course, be understood that although the thinwalled side of the skirt is so constructed and arranged that it will be resiliently collapsed or contracted before enough pressure is applied thereto to cause the piston to bind in the cylinder, it is sufficiently strong to insure that the material of which it'is made will not be strained beyond its elastic limit and will, therefore, return to its normal shape when the pressure on it is relieved by cooling of the piston. It will also be understood that the characteristics of the thin-walled side of the skirt referred to in the preceding sentence will depend on, among other things, the length of the slot 25 and, consequently, that the slot 25 may extend the full length of the thin-walled side of the skirt in the pistons'for some engines and only a part of the length thereof in the pistons for other engines.

During the operation of the engine, the head of the piston becomes heated to a high temperature. A portion of the heat from the head escapes therefrom directly into the thick-walled side of the skirt whence it passes into the cylinder walls, while another portion of the heat escapes into the columns 26 and bosses 21 whence it passes, through the webs 28, into the thick-walled side of the skirt and the cylinder walls. Since there is no direct path by which heat can travel from the head into the thin-walled side of the skirt, this portion of the skirt becomes less highly heated than it would if it were directly connected to the head and, consequently, the total expansion of the piston and the tendency of the piston to bind in the cylinder is reduced.

Although I have shown and described a preferred embodiment of my invention, it is to be understood that this has been done by way of example and not by way of limitation, and that the scope of my invention is to be determined only by the appended claim.

I claim:

A piston which includes a head, a skirt which is joined to the head throughout a part of its circumference and is disconnected from the head throughout the remainder of its circumference, openings in the skirt intermediate the portion which is connected to the. head and the portion which is disconnected therefrom, and wrist pin bosses carried by the head and located in said openings out of contact with the skirt,the first mentioned portion of the skirt being of greater thickness than the portion on the opposite side of the wrist pin bosses and of less thickness than the portions of the skirt under the openings.

FRANKN.NUTI'.

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