US2119137A - Piston - Google Patents

Description

4 May 31, 1938. G L, MOORE 2,119,137

PISTON Filed July 25, 19 33 i 7 5 Smaento:

6508i? 1. Mae-1 (Ittorneg Patented May I 31, 1938 PISTON George L. Moore, Cleveland, Ohio. assignor, by mesne assignments, to The Cleveland Trust Company, Cleveland,

Ohio, as trustee Ohio, a corporation of Application July 25, 1933, Serial No. 682,051

4 Claims.

This invention. relates to pistons for internal combustion engines and the like, and particularly to pistons composed of aluminum alloy or The principal object of this invention is to provide a relatively simple and cheap piston construction which -may be fitted when cold to a cylinder with a sufliciently small clearance to avoid piston slap and to reduce oil pumping and which will yield to permit thermal expansion without binding in the cylinder while at the same time being designed-to provide ample bearing surfaces for transmitting the thrust loads to the cylinder walls without excessive friction at isolated points and to permit a free flow of heat from the piston to the cylinder. walls and to operate in a cylinder at all times without excessive friction and without premature fatigue failure.

The present invention consists primarily in a novel arrangement of slotting a piston of the full trunk type and providing means for yieldably pressing the slotted parts in such a mannerfthat the piston will fit the cylinder without slapping or rattling at all temperatures and will also reciprocate freely without binding at all temperatures. One object of this invention is to provide a piston with a skirt slotted on one side only and the slotted portions pressed out yieldably in such a manner that the piston when cold will fit the cylinder with a relatively close clearance along the diameter perpendicular to the wrist pin bosses and with a relatively large clearance along the diameter parallel to the wrist pin axis and with a clearance increasing in both directions from the center of the slotted face more rapidly than from the center of the opposite face so as to provide a relatively wide bearing on the unslotted face when the piston is cold to prevent lateral movement of the piston along the wrist pin axis. Other objects of the invention are to avoid fatigue of the slotted portions of the piston by initially yieldably pressinglthe slotted portions outwardly; to apply the yieldable pressure to the slotted portion of the skirt through a relatively wide vertical range in the zone of the applica tion of the lateral thrust; to mount an expander element in a piston in such a manner that thermal expansion of the head will reduce the amount the skirt is held expanded; and to provide a simple and cheap expander element which may be easily constructed and assembled in the piston.

Other objects and advantages of this inven tion relating to details of construction and economies of manufacture will appear hereinafter.

In the accompanying drawing which illustrates a preferred embodiment of the invention:

Figure 1 is an elevational view of a piston constructed in accordance with this invention;

Figure 2 is an elevational view taken from a point at right angles to Figure 1;

Figure 3 is a cross section taken on the line 3--3 of Figure 1;

Figure 4 is a view corresponding to Figure 3 of a modified embodiment of the invention.

Referring to the drawing the numeral l0 designates the head of the piston which is preferably constructed of aluminum alloy or similar light metal. The head is formed with 'a depending ring flange H which may be provided in the usualmanner with a series of ring grooves l2. The piston is preferably initially cast in the form of a full trunk type piston including a cylindrical skirt l3 integral with the lower edge of the ring flange and having opposed wrist pin bosses l4 formed therein. Preferably the piston is also cast with relieved areas l5 in the region of the wrist pin bosses. After casting the piston is completed by machining operations.

The skirt of the piston is partially separated from the head by a horizontal arcuate slot l6 which is preferably cut through the lower-most ring groove as shown and extends on one side of the piston through less than 180 degrees with its ends spaced from the vertical plane through the wrist pin axis. Preferably the slot terminates in holes I! drilled through the piston wall. The portion of the wall of the piston separated from the head by the horizontal slot l6 constitutes one thrust face and is designated by the numeral l8. The opposite side of the piston, forming the thrust face l9 preferably remains integrally attached to the head.

The thrust face I8 is rendered yieldable by means of a substantially vertical slot 20 cut through this thrust face at about its center intersecting the horizontal slot l6 and preferably extending completely through the height of the skirt as illustrated in Figure 2. This arrangement of slots with the horizontal slot l6 separating the upper edge of the thrust face l8 from the head and the substantially vertical slot 20 dividing the thrust face 18 provides a pair of relatively yieldable leaves which may be flexed inwardly toward each other to reduce the diameter of the skirt at all points through the vertical height and prevent binding of the piston in the cylinder.

The ring flange H of the piston is preferably ground to a sufllciently small diameter so that it does not contact the cylinder walls at any temperature in accordance with the usual practice.

' The skirt of the piston is preferably ground to a cylindrical contour so that all portions of the skirt are circular in horizontal section except for the relieved areas II in the region of the wrist pin bosses. The skirt is preferably ground to a diameter small enough to leave a large clearance from the wall of the cylinder in which the piston is designed to operate; that is, a clearance corresponding to about the clearance that would be necessary for a full trunk type piston having no slotted or yieldable portions.

A spring expander 2| which may be constructed of any suitable metal having the'necessary resilience and fatigue resistance such as spring steel is assembled within the piston after the completion of the grinding and slotting. The expander is preferably of ferrous metal so as to expand but slightly when heated. The expander 2| is of substantial vertical height as illustrated in Figure 1 and is curved to provide a central portion 22 to engage the interior of the wall of the thrust face l8 at about its center and curved ends 23 to seat against the wrist pin bosses H. Preferably the wrist pir. bosses H are formed with seats 24 curved to fit the'ends 23 of the expander throughout its length. Integral lugs or bosses 25 may also be formed at the top and bottom edges of the seats 24 to embrace the ends 23 of the expander and retain the same against vertical movement or dislocation.

The expander 2| is arranged to press against the inner surface of the wall of the thrust face |8 with sufiicient force to initially spread the separated leaves of the thrust face l8 outwardly as illustrated in Figure 3. The piston may then be assembled within a cylinder, indicated in cross section at C in Figures 3 and 4, with the centers of the two thrust faces l8 and I9 in close clearance relation to the wall of the cylinder. The thrust face I9 is curved with a slightly greater degree of curvature than the wall of the cylinder, since this thrust face has been ground to a circular contour about the center 26 as indicated in Figure 3 which is spaced slightly toward the thrust face |9 from the center line or axis of the cylinder 21. Accordingly, the clearance of the thrust face Hi from the cylinder wall increases slightly in both directions from the center of the thrust face as shown in Figure 3. The thrust face I8 is pressed out of its circular contour by the expander 2| so that this thrust face has an ovate sectional contour. The clearance of the thrust face l8 increases in both directions from its vertical center relatively rapidly so that a relatively large clearance exists between the cylinder wall and the thrust face I8 at the adjacent ends of the relieved areas IS.

The piston is fitted to the cylinder in this manner while the parts are cold. Piston slap in the direction perpendicular to the wrist pin axis is avoided by the relatively close clearance at the ends of this axis. Lateral movement of the piston along the wrist pin axis is prevented by the relatively small clearance between the thrust face I9 and the cylinder wall which is sufl'iciently small at the adjacent ends of the relieved areas I5 to prevent an audible slap in the event the piston moves along the wrist pin axis within the cylinder. As the piston heats up to working temperature the head and ring flange expand and while retaining their circularcontour become larger in diameter. Exactly the same action takes place in the portion of the skirt integrally connected to the head which includes the thrust face I9 and the portions of the skirt carrying the wrist pin bosses ll. The entire piston is thereby caused to move to the right in the cylinder as seen in Figure 3 until the center 2! coincides with the axis of the cylinder 21. This ,movement and expansion of the parts is permitted by the yieldable leaves of. the thrust face II which are pressed inwardly toward each other against the resilience of the spring 2|, partially closing the slot 20 from its expanded position.

The curved ends 23 of the expander 2| are alto which it was initially ground so that the piston fits the cylinder throughout its circumference in substantially the same manner as a full trunk piston. Thesubstantially vertical slot 20 may be made extremely narrow initially so that it is opened when the piston is cold by the expander 2| and is substantially closed when the piston reaches full operating temperature.

The expander 2| is preferably made relatively stiff so that it yields but slightly under the lateral thrusts of the piston against the cylinder wall due to the angularity of the connecting rod so as to avoid excessive flexing and consequent fatigue of the separated portions of the thrust face It and the expander 2|. When the piston expands the bosses l4 are moved apart slightly due to the increase in diameter of the piston in the direction of the wrist pin axis. This separation of the bosses correspondingly separates the ends 23 of the expander 2| which are seated in the opposite bosses and thereby permits the separated portions of the thrust face |8 to move inwardly through a greater distance than is permitted when the piston is cold. Thus the necessary flexibility is provided at all temperatures, although the stiffness of the expander 2| prevents the separated portions of the thrust face i8 from being pressed completely back to their initial truly circular contour until the bosses |4 have been separated slightly by the thermal expansion. In other words the stiffness of the expander 2| is such that the distance through which the separated portions of the thrust face l8 may yield under the lateral thrusts to which the piston is subjected issubstantially less at any given position of the Wrist pin bosses than the total distance through which the separated portions move during the heating up of the piston to full operating temperature. Normally the piston is assembled within the cylinder so that the maximum thrust, or in other words, the lateral thrusts of the power stroke, are taken by the thrust face I9 while the substantially smaller thrusts of the compression stroke and the inertia of the piston are taken by the thrust face l8.

A slightly modified embodiment is illustrated in Figure 4 in which the skirt of the piston instead of being ground to a circular sectional contour initially is cam ground to an ovate sectional contour with the major axis perpendicular to the wrist pin bosses and a greater increase in clearance in both directions from the center of the minimum thrust face i8 than at corresponding points on the maximum thrust face i8, as disclosed in the copending application of Frank Jardine, Serial No. 619,947, filed June 29, 1932. The Operation of this form of the piston is substantially the same as that previously described except that the expander 2| instead of initially forcing the leaves of the thrust face outwardly through a sufficient distance to provide the desired close clearance at the centers of the thrust faces acts primarily to restrain these leaves of the thrust face i8 and thereby does not initially stress the metal of the thrust face to such a great extent. The expander 2! serves to prevent excessive flexing of the leaves of the thrust face 18 under lateral thrust which would'otherwise be permitted with the slot out completely through the height of the skirt as illustrated.

It will be clear that the arrangement of the expander element 2! may, if desired, be incorporated in any type of slotted piston in engagement with the slotted part to perform the functions described. Various other rearrangements of parts and modifications of structural detail of either the piston or expander may be resorted to without departing from the scope of the invention as defined in the following claims.

I claim:

1. An internal combustion engine piston including a head having a substantially cylindrical depending ring flange, and a skirt partially integral with the lower edge of said ring flange, and carrying aligned wrist pin bosses, said skirt being formed with opposed thrust faces between said bosses, one of said thrust faces being separated at its upper edge from said head and havinga substantially vertical slot formed there- -in, said skirt being initially ground to a substantially circular sectional contour with a diameter substantially less than the diameter of a circular cylinder in which the piston is to operate, and means pressing said slotted thrust face outwardly beyond its initial contour so that the piston when cold fits the cylinder with a relatively small clearance at the ends of the diameter perpendicular to the wrist pin' axis, said means being yieldable so that said piston may return to a substantially circular contour with a relatively small clearance from said cylinder throughout its circumference when said piston is heated to operating temperature.

2. An internal combustion engine piston composed of light metal alloy, including a head having a substantially cylindrical depending ring flange and a skirt partially integral with the lower edge of said ring flange and carrying aligned wrist pin bosses, said skirt being formed with opposed thrust faces between said bosses, one of said thrust faces being separated at its upper edge from said head and having a substantially vertical slot formed therein, said skirt being initially ground to a substantially circular sectional contour with a diameter substantiallyless than the diameter of a circular cylinder in which the pis-- ton isto operate, and means composed of ferrous metal pressing said slotted thrust face outwardly beyond its initial contour so that the piston when cold fits the cylinder with a relatively small clearance at the ends of the diameter perpendicular to the Wrist pin axis, said means being yieldable so that said piston may return to a substantially circular contour with a relatively small clearance from said cylinder throughout its circumference when said piston is heated to operating temperature.

3. An internal combustion engine piston for operation in a circular iron cylinder of an internal combustion engine, said piston being composed of aluminum alloy and including a head having a ring flange, a skirt partially integral at its upper edge with the lower edge of said ring flange having aligned wrist pin bosses formed therein and including opposed thrust faces intermediate said wrist pin bosses, one of said thrust faces being separated at its upper edge from said ring flange and being formed with a substantially vertical slot, said skirt being ground to a substantially circular sectional contour with a diameter excessively less, when the piston is cold, than the diameter of the engine cylinder in which the piston is to operate, when cold, and means pressing said slotted thrust face outwardly beyond its initial contour and into an oval sectional contour, said means being arranged to react against said wrist pin bosses so as not to distort the other of said thrust faces, said skirt when cold fitting the engine cylinder with a relatively close clearance at the ends of a. diameter perpendicular to the wrist pin axis and with said slotted thrust face having a minimum clearance at its center, small enough to prevent piston slap and a progressively increasing clearancewith respect to the cylinder at points spaced on each side of the center, and with the other thrust face having a minimum clearance at its center and a progressively increasing clearance from the cylinder wall at points spaced on each side of its center substantially less than the clearance of corresponding points on the slotted thrust face and insufiicient to permit piston slap from lateral play of the piston along the wrist pin axis, said means being yieldable to permit said slotted thrust face to return to its initial contour and said piston skirt fitting the engine cylinder with a relatively close clearance throughout its periphery when said piston is heated to full operating temperature.

4. The method of making a light metal piston for internal combustion engines which comprises machining the piston by grinding and cutting operations to form a skirt having cylinder engaging surfaces all of which have a circular sectional contour, and a slotted portion on one side between the wrist pin bosses, and resiliently securing said slotted side of the skirt pressed outwardly at its center with respect to the wrist pin bosses in such a manner as to change the sectional contour of the slotted side to a semi-elliptical sectional contour with its major axis perpendicular to the wrist pin axis.

GEORGE L. MOORE.

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