US2044074A

US2044074A - Piston

Info

Publication number: US2044074A
Application number: US682055A
Authority: US
Inventors: Jardine Frank
Original assignee: Cleveland Trust Co
Current assignee: Cleveland Trust Co
Priority date: 1933-07-25
Filing date: 1933-07-25
Publication date: 1936-06-16
Anticipated expiration: 1953-06-16

Description

F. JARDUNE June is, @936 PISTON Filed July 25,

Brmentor Patented June 1936 UNITED STATES PATENT OFFICE mesne assignments, to

The Cleveland Trust Company, Cleveland, Ohio, a corporation of Ohio, as trustee Application July 25, 193s, serial 10,682,055 1 claims. (on 30s-11)' This invention relates to pistons for internal combustion engines and the like, and particularly to pistons composed of aluminum alloy or other metal alloy having a higher co-efflcient of thermal expansion than the material of the cylinder in which the pistonis to operate.

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 sufficiently 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 operate in a cylinder at all temperatures without excessive friction and without premature fatigue failure from the lateral thrust loads.

The present invention consists primarily in a novel arrangement of slotting, grinding and relieving a piston skirt to permit the piston to fit closely to a cylinder wall at all temperatures without slapping when cold or binding when hot which may be readily produced from a simple and cheap casting. One object of this invention 'is to provide a piston in which the thermal expansion of the skirt is absorbed at the upper portion of the skirt by distortion from an ovate to a cylindrical form and in which the lower portion of the skirt is formed to closely guide the piston at all temperatures and to absorb thermal expansion by means of one or more slots. Another object of the invention is` to provide a piston skirt which is substantially oval in section at its upper portion and substantially circular in section at its lower portion. Another object is to provide a piston skirt having at its upper portion ovate thrust faces separated from the head and de- .'ormable to absorb thermal expansion and at its lower portion a substantially cylindrical band slotted in such a manner as to absorb thermal expansion and partially separated from the up- -er part of the skirt to retard the flow of heat nd prevent the deformationl of the upper part of the skirt from being transmitted to the lower part.

Other objects and advantages of this invention 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;

Fig. 2 is an elevational view taken from a point 'at right angles to Fig. 1;

Fig. 3 is a cross section taken on the line 3-3 of Fig. 1; and

Fig. 4 is a cross section taken on the line 4-4 of Fig. 1.

Referring to the drawing the numeral I desig- 5 nates the head of the piston which is preferably constructed of aluminum alloy or similar light metal alloy. The head is formed with a depending ring flange I I which may be formed in the usual manner with a series of ring grooves I2. The piston is preferably initially cast in the form of a full trunk type piston including a cylindrical skirt I3 integral with the lower edge of the ring flange and having opposed wrist pin bosses Il formed therein. Preferably the piston is also cast with reliefs I5 of substantial extent disposed about the ends of the wrist pin bosses and extending from the ring flange a short distance below 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 means of two substantially horizontal arcuate slots I6 and Il leaving integral connectors I8 between the ends of the slots disposed above the wrist pin bosses I4 and 25 connecting the skirt to the head.

The portion of the skirt between the wrist pin bosses and below the slot I6 designated at I9 is termed the maximum thrust face and is designed to be arranged in the cylinder to receive the `lateral thrust of the power stroke of the piston. The opposite side of the piston skirt below the slot Il is designated by the numeral 20 and is termed the minimum thrust face. The minimum thrust face is designed to receive the lateral thrust of the piston in the cylinder during th'e compression stroke, and the inertia thrusts.

The piston skirt is formed with a circumferential substantially horizontal groove 2I arranged about on a level with the lower edges of 40 the cast reliefs I5. Below each of the reliefs I5 a slot 22 is cut through the wall of the piston in the bottom of the groove 2 I, the middle of each slot 22 preferably being located about in vertical alignment with the axis of the wrist pin bosses Il. As illustrated in Figures 1 and 2 the slots 22 are preferably arranged at the bottom edge of the cast reliefs I5. A substantially vertical slot 23 is cut in the thrust face 20 of the piston and extends from the open end of the piston upwardly into the skirt and terminates as illustrated in Figure 2 a short distance above the horizontal plane of the wrist pin axis. Preferably a hole 24 is drilled through the wall of the piston and forms the terminus of the slot 23. 'Ihe 55 upper end of the slot 23 is located a substantial distance below the horizontal slot Il, leaving a. circumferentially continuous band of metal below the level of the slots I6 and I l and above the upper end of the slot 23.

The relieved areas I5 may, if desired, extend a greater distance into the thrust face 20 from the wrist pin axis than into the thrust face I9, as illustrated in Figure 1.

The ring flange I I is ground to a diameter suificiently small so that it does not engage the cylinder wall at any temperature. The skirt of :he piston between the groove 2I and its upper edge is ground with an oval sectional contour with its major axis perpendicular to the wrist pin axis as indicated by the diameter a in Figure 3. The minor axis of the oval is indicated by the diameter b in Figure 3. The portion of the skirt below the groove 2I is preferably ground to a circular sectional contour having a relatively close iit to the cylinder wall as shown in Figure 4. In Figures 3 and 4 the engine cylinder is indicated at C and is shown as being truly circular in section.

When the piston is cold and is assembled within a cylinder the upper portion, which is provided With the oval sectional contour, has a relatively close clearance to the cylinder wall at the ends of the diameter a as indicated in Figure 3. The clearance between each of the thrust faces and the cylinder wall increases in each direction from the diameter a until the edge of the adjacent cast relief I5 is reached. The relief I5 provides a relatively large clearance on each side of the piston at the ends of the wrist pin axis and the relieved areas do not at any time contact with the cylinder wall. Below the groove 2I the piston skirt is preferably ground with a circular sectional contour and has a relatively close fit to the cylinder wall as indicated in Figure 4.

When the piston is heated up to operating temperature the head II! and ring flange II expand uniformly in all directions. The expansion of the head at right angles to the wrist pin bosses has no eifect upon the skirt, since the skirt is separated from the head in this direction by the slots I6 and Il. 'I'he expansion of the head parallel to the wrist pin axis carries out with it the integral connectors I8 which connect the head to the skirt and consequently deforms the continuous band above the upper end of the slot 23, increasing the length of the minor axis of the oval formed by this band and consequently tending to decrease the length of the major axis perpendicular to the wrist pin axis. 'I'his connection of the head to the skirt prevents the full expansion of the head from being transmitted mechanically to the skirt of the piston along the diameter a in Figure 3, and the expansion of the piston along this diameter at the upper part of the skirt is therefore solely the expansion due to the temperature of t 's part. By reason of the slots I6 and I1. the ends of which are disposed a substantial distance past the edges of the relieved areas I5, the upper portion of the skirt is rendered flexible suiilciently to permit it to be deformed to prevent binding or scoring when the skirt bears upon the cylinder wall along the diameter a. In other words the relatively narrow bearing faces I9 and 20 at the upper edge of the skirt are prevented from being forced outwardly into tight engagement with the cylinder wall. the skirt being deformed to permit outward movement toward the cylinder wall at the relieved portions of the upper part of the skirt to compensate for the tendency of the skirt to expand diametrically.

The heat flowing from the head of the piston 5 into the skirt is transmitted to the bearing surfaces and dissipated by these surfaces to the cylinder wall. The width of the bearing areas on each side of the piston increases in a downward direction by reason of the wedge shape of the cast reliefs I5 as indicated in Figure l and consequently the amount of heat transferred to the cylinder wall increases toward the lower end of the piston. Transmission of heat to the lower portion of the skirt below the groove 2I is pre- 15 vented in the vertical zone of the relieved areas I5 by the slots 22. Accordingly, the lower portion of the piston is maintained normally at a substantially lower temperature than the upper portion. The thermal expansion of the lower portion of the piston is accommodated by the substantially vertical slot 23 which may partially close to absorb the expansion. The deformation of the upper portion of the piston skirt and the change of the oval contour to a more nearly circular contour is prevented from deforming or afiecting the lower portion of the piston by reason of the slots 22 which separate the upper and lower portions of the piston in the vertical zone of the connectors I8. As a consequence the expension of the skirt is absorbed at the upper part of the skirt primarily by means of deformation of this portion of the skirt from an oval contour to a substantially circular contour and the expansion of the piston at the lower portion is absorbed by the slot 23. The effect of the slot 23 also extends above the slots 22 and overlaps the deformin'g effect through a portion of the height of the skirt.

It will be seen from Figure 3 that the oval 40 contour of the upper portion of the skirt when the piston is cold leaves a relatively large clearance between the cylinder wall and all portions of the skirt except at the ends of the diameter a. Lateral sliding and slapping of the piston along the diameter b as a result of the large clearance at the ends of this diameter is prevented by the integral circular` portion at the lower end of the piston which has a close engagement with the cylinder wall throughout its 50 circumference. This close tting relationship of the portion of the piston below the horizontal slots 22 in combination with the effect of the wrist pin itself, which prevents lateral movement of the piston except bodily movement directly along the wrist piny axis prevents lateral movement of the piston.

If desired, the cast reliefs I5 may be omitted and the necessary large clearance to make the upper portion of the piston sufliciently oval may be obtained solely by grinding. Similarly these reliefs may, if desired, be made symmetrical with respect to the wrist pin axis. The lower portion of the skirt may also be ground to other shapes than a true circular sectional contour, it being only necessary that the portion of the lower part of the skirt in line with the wrist pin axis have a close enough nt to the cylinder when cold to prevent lateral sliding of the piston along the Wrist pin axis. Various other modifications and I rearrangements of structural detalls may be resorted to without departing from the scope of the invention as defined by the following claims.

I claim:

1. An internal combustion engine piston formed .of light metal alloy and comprising a head having a substantially cylindrical depending ring flange, a skirt having aligned wrist pin bosses formed therein and having opposed thrust faces between said wrist pin bosses, said skirt being integrally connected with said Vring flange i in the vertical zone of said wrist pin bosses and being separated at its upper edge from said ring flange by horizontal slots above said thrust faces, the upper portion of said thrust faces having an ovate sectional contour with its greater diameter perpendicular to the wrist pin axis and including a circumferentially continuous band, and the lower portion of the skirt having a substantially circular sectional contour and being yieldable by means of a substantially vertical slot extending upwardly from the open end of the piston skirt.

2. An internal combustion engine piston formed of light metal alloy comprising a head having a substantially cylindrical depending ring flange and a skirt having aligned wrist pin bosses formed therein, said skirt being integrally connected to said head in the vertical zone of said wrist pin bosses and the remainder of said skirt being separated from said head by substantially horizontal slots,A a portion of said skirt above the level of-said wrist pin bosses being circumferentially integral and having cylinder bearing portions with an ovate sectional contour with its greatest diameter perpendicular to the wrist pin axis and a portion of said skirt below the level of said wrist pin bosses having a substantially circular sectional contour and being yieldable by means of a substantially vertical slot extending therethrough.

3. An internal combustion engine piston formed of light metal alloy and comprising a head having a substantially cylindrical depending ring flange, a skirt having aligned wrist pin bosses formed therein and having opposed thrust faces between said wrist pin bosses, said skirt being integrally connected with said ring flange in the vertical zone of saidwrist pin bosses and being separated at its upper edge from said ring flange by horizontal slots above said thrust faces, the upper portion ofsaid thrust faces having an ovate sectional contour with its greatest diameter perpendicular tothe wrist pin axis and including a circumferentially continuous band, and the lower portion of said skirt having a substantially circular sectional contour and being yieldable by means of a substantially vertical slotextending upwardly from the open end of the piston skirt, said lower portion of the skirt being partially separated from the remainder of the skirt by substantially horizontal slots below the wrist pin bosses.

4. An internal combustion engine piston formed of light mtal alloy comprising a head having a substantially cylindrical depending-ring flange and a skirt having aligned wrist pin bosses formed therein, said skirt being integrally connected to said head in the vertical sone of said wrist pin bosses and the'remainder of said skirt being separated i'rom said head by substantially 'der of the skirt by substantially horizontal slots below the wrist pin bosses.

5. An internal combustion engine piston composed of light metal alloy comprising a head having a substantially cylindrical depending ring flange, aligned wrist pin bosses below and integrally connected to said ring flange and a skirt including opposed thrust faces integrally connected to said wrist pin bosses and separated at their upper edges from said ring flange, a portion of said skirt above said wrist pin bosses being circumferentially continuous and integral with said ring flange and wrist pin bosses and having cylinder bearing portions with an ovate sectional contour with its major axis perpendicular to the wrist pinl axis, and another portion of id skirt having a substantially circular sect onal contour and being yieldable by means of asubstantially vertical slot extending therethrough.

, 6. 'An internal combustion engine piston composed of light metal alloy comprising a head havingA a substantially cylindrical depending ring ange, aligned wrist pin bosses belowand integrally connected to said ring ange and a skirt including opposed thrust faces integrally connected to said wrist pin bosses and separated at their upper edges from-said ring flange, a portion of said skirt above said wrist pin bosses being circumferentially continuous and integral with said ring flange and wrist pin bosses and having cylinder bearing portions with an ovate sectional contour with its major axis perpendicular to the wrist pin axis, and another portion of said skirt having a substantially circular sectional contour and being yieldable by means of a substantially vertical slot extending therethrough, said last mentioned portion of said skirt being partially separated from the remainderV of the skirt by opposed horizontal slots.

7. A piston comprising a head having a depending cylindrical ring flange, aligned wrist pin bosses integrally connected to said ring flange.. and a skirt including opposed thrust faces inte gral with said wrist pin bosses and separated at their upper edges from said ring ilange, a substantially vertical slotin oney of said thrust faces extending through only a portion of the height thereof leaving o portion of the vertical height ovate sectional contour with its greatest diameter perpendicular to the wrist pin axis.

' FRANK JARDINE.