US2472288A - Piston - Google Patents

Description

June 7, 1949. ENDSLEY ETAL 2,472,288

PISTON F 'iled Jan. 26, 1948 2 Sheets-Shet J.

INVENTORS Lows E. ENDSLEY WESLEY W. SHETTLER JOHN HOWARD LENTELL ATTORNEY .Fum 7, 1949. L. E. ENDSLEY ETAL 2,472,288

rrswou I Filed Jan. 26, 1948 2 Sheets-Sheet 2 INVENTORS Lows E. .ENDSLEY WESLEY w SHETTLER 60 JOHN HQWARD LENTELL.

ATTORNEY Patented June 7, 1949 PISTON Louis E. Endsley, Pittsburgh, Pa., and Wesley W.

Schettler and John Howard Lentell, Beloit, Wis.,

assignors to Fairbanks, Morse & 00., Chicago,

111., a corporation of Illinois Application January 2c, 1948, Serial No. 4,244

This invention relates to pistons for internal combustion engines, and is particularly directed to the improvements in the construction of and provisions for cooling the piston.

The present invention has as a general object the provision of an improved piston construction and one that will better withstand heavy duty loads and high and changeable temperature conditions.

In its more specific aspects, the objects hereof are to provide an improved piston body which will posses structural characteristics enabling its greater resistance to mechanical loads and thermal expansion forces, and to provide'a piston insert unit which is constructed for cooperation in combination with the piston body to direct a cooling medium into the critical areas of the piston body or crown and to retain a quantity of such cooling medium in condition for forceable circulation onto the critical areas during piston operation by reason of the inertia forces incident to piston motion.

Another object of the invention resides in the construction of a piston body having an improved crown portion which will be substantially free of load and thermal stresses and which is provided with internal and depending strut elements arranged to distribute the forces incident to piston operation and provide an improved means where by the circulation of .a cooling medium may be more intimately directed over the critical area to carry ofi the heat imparted to the crown and adjacent portion of the piston.

Other objects of the present invention will appear from the following detailed description of a single preferred embodiment, reference being had to the accompanying drawing, wherein:

Fig. 1 is a top plan view of the piston showing in dotted outline the arrangement of depending struts;

Fig. 2 is a sectional elevation through the piston and insert assembly, as seen at line 2-2 of Fig. 1;

Fig. 3 is a further sectional elevation taken along line 33 in Fig. 1 and wherein portions of the insert and connection rod assembly are omitted to show additional details;

Fig. 4 is a sectional view taken at the top plane of thepiston insert member as indicated at line 4-4 in Fig. 2, and wherein further details of the assembly are shown to advantage.

The preferred embodiment of the invention includes a piston body I having a crown portion 1 I 3 Claims. (Cl. 309-16)v by a central area ll! of spherical and convex form and a peripheral area I4 of a concavo-convex form which rises above the spherically convex central area and is joined at its outer margin with the skirt portion, specifically with the cylindrical crown wall l5 thereof above the relatively thickened ring boss Hi. In the formation of the piston crown, a series of inner and outer strut members are integrally cast at the under surface to extend axially of the piston. The inner series of struts ll are arcuate in transverse section and are spaced to form slotted openings or ports 18 therebetween. In the present construction shown by Figs. 1 and 2, the inner struts I! are four in number and a similar number of slot-like ports l8 are provided therebetween. The outer series of struts l9, also arcuately formed in transverse section, are located substantially opposite and in symmetrical relation with the slot-like ports l8 and are spaced to form a second series of slot-like ports 20 therebetween. Thus the innerand outer series of struts and slot-like ports, there being four in each series, are relatively staggered or angularly off-set, each with the others, to define a plurality of tortuous passages between the central pocket or chamber 2! defined in the under surface of the spherically concave crown I3 by the struts ii and the outer or peripheral cavities 22 formed adjacent the under surface of the concavo-convex crown periphery I l.

The outer cavities 22 in the crown portion of the piston body In are defined in partby adjacent strut members l9, the outer cylindrical wall i5 adjacent the crown, and by radially directed boss formations or webs 23 which are integrally formed with and connect the struts l9 and the thickened zone of the ring boss Hi. These webs 23 are free of any connection with the piston crown wall portion it (see Fig. 3) so that the flexibility in this wall portion is insured. Since each of the webs 23 is free of contact or connection with the crown wall portion it, it will appear that each of the cavities 22 is in communication with the two adjacent cavities to form a complete passage about the upper margin of the crown between the cylindrical wall l5 and the crown wall Id of concavo-convex configiiration.

The lower end of each of the strut members All in the inner series and of the strut members it in the outer series are machined off to a common planar relation. At the time of this machining the lower zone of the ring boss I6 is internally machined to provide a cylindrical surface 28 which is concentric with the axis of the piston amazes body I 8. and an annular shoulder or abutment 21 is also formed with its axially directed face located in the common plane of the struts l1 and [8. The cylindrical surface 28 and annular shoulder 21 provide a seat for the upper end of the piston insert or connecting rod bearing carrier later to be described.

The piston skirt i2 is characterized by its substantially symmetrical and relatively thin wall construction which extends below the ring boss 18 and terminates in a thickened end portion 28 adapted to carry oiling rings in suitable ring grooves 30. The inner surface of this thickened end 28 of the piston skirt is machined to provide a cylindrical surface 3i having a .diameter substantially equal to that of the upper cylindrical seat 26. The ring boss I 8 adjacent the upper end of the piston body is also machined to provide external grooves 32 for suitable compression rings.

Referring to Figs. 2; 3 and 4, the present improvements in piston construction may be seen to include-an insert member 35 comprising a unitary cast body of generally cylindrical shape (Fig. 4) in plan. The upper portion of this insert body 35 is provided with inwardly and upwardly curved wall portions 38 separated at four equally spaced zones by boss projections 31, the latter projections extending into an upper, planar top surface 38 having the symmetrical marginal contour clearly indicated inFig. 4. Each of the.projections 31 is formed with a cylindrical outer surface 39 which is made accurately to flt in the piston body seat defined by the cylindrical "wall 28 and annular abutment 21 (Fig. 3). In theforming of the insert body 35, a longitudinal boss or column element 40 is provided below each projection 31, and these column elements are axially drilled to form stud-receiving openings 4| which open through the top surface 38 of the insert, The lower end of the insert body 35 is formed with an annular and radially directed flange 42 having its outer face 43 machined to a true cylindrical form suitable for effecting a close sliding fit with the adiacent surface 3! on the piston skirt end portion 28 (Figs. 2 and 3).

Additionally, the insert body 35 is provided at diametrically opposite sides with an enlarged boss 45 (one being shown in Fig. 3) which is suitably bored out at 48 to form a bearing surface for the hollow gudgeon pin 41. This pin works in a bushing 48 fitted to the bore 48 in the insert boss 45. The space between these insert bearing bosses 45 'forms the slot to receive the upper end bearing 50 of the usual connecting rod The connecting rod bearing 50, through'suitable bushings, has a working fit with the central portion of the gudgeon pin 41, and the upper end of this connecting rod bearing projects into a recess 52 formed at the under side of the central area of the insert body 35. In Figs. 2 and 3, the central area of the insert top face 38 is apertured at 53 to afford communication between the cavity 2| in the under side of the piston crown l I and the recess 52 in the insert body 35. Means for sealing the recess 52 from the rest of the insert area therebelow is providedin the form of a sealing ring element 55 having a spherically formed lower face which seats against the adjacent face of the connecting rod, as shown in Figs. 2 and 3. This sealing ring is held in position in a shouldered recess 58, and by the force of a compression spring 51, the spring bearing on the ring and against a flange adjacent the aperture 53 in the upper wall 38 of the insert.

In conjunction with the above described details, the connecting rod II is longitudinally drilled to provide an oil supply passage 83 leading from a suitable connection at the crankshaft (not shown) to the internal annular oil groove 8i formed in the bearing 88. This groove 8i extends completely around the gudgeon pin and communicates with the insert recess 53 through the axal port 82 in the upper end of the connecting ro When effecting assembly of the piston l3 and the insert body 35, after the insert and connecting rod are fully assembled as shown, the piston is positioned over the insert such that the cylindrical surface 39 at the upper end of the insert engages in the piston seat defined by surfaces 28 and 21, and the lower surface 43 at the insert flange 42 engages with the cylindrical surface 3| at the lower end 28 of the piston skirt. The piston and insert are relatively rotated until the stud receiving passages 4i of the insert line up with the threaded apertures 83 (Figs. 1 and 3) in the piston webs 23 adjacent the outer series of struts l8. When this is accomplished the holding studs 84, there being four such elements, may then be inserted and threaded up in the apertures 83, and the clamping nuts 85 threaded on the lower projecting end of the studs. The nuts 85 are turned up to secure the piston and insert in final assembly and to bring the top surface 38 of the insert into abutment with each of the struts l1 and i3 dependingly carried by the under surface of the piston crown Ii.

The piston skirt portion I2 and the adjacent walls 38 of the insert are relatively spaced and thereby coact to form an annular piston skirt chamber 81 which is closed at its bottom by the insert flange 42 and is in open communication with the outer cavities 22 in the piston head end or crown by way of the passages formed between the upper curved insert wall 38 and the cylindrical surface 28 of the piston between the insert projections 31. The resulting chamber 81 is provided with a plurality of outlet ports 88 (Fig. 2) located at a predetermined position above the closed bottom zone of the skirt chamber 81 and in the curved portion of the insert wall 38. These ports 88 (Figs. 3 and 4) are grouped in pairs at diametrically opposite zones of the insert and open from the chamber 81 to the interior 89 of the insert body 35.

When in service operation the interior of the piston, and particularly the internal surfaces of the crown I I, annular wall I4 and upper cylindrical wall l5 are bathed by a volume of oil supplied through the connecting rod passage 88 under pressure from the engine system. This cooling oil flows around the gudgeon pin 41 to the upper port 82 by way of the groove 8!, and is forceably directed into the crown recess 2i where it can impinge upon the central crown surface and then flow radially outwardly and about the inner series of struts l1 and outer struts 13 to the cavities 22. The oil then flows into the annular chamber 81 and a quantity thereof is always contained by this chamber, the excess passing through outlet ports 88 to the interior space 88 of the insert body 35 for return to the engine crankcase and recirculation in the usual manner.

As an incident to the rapid reciprocatory motion of the piston and insert assembly, the cooling oil in the skirt chamber 81 will be forceably projected into the cavities and wall areas of the piston crown portions during the outward movement of the piston and made to wash these surfaces and absorb the heat transmitted from the combustion side at an accelerated rate. Dur-,

ing opposite, inward piston movement, the heated oil will be dashed into the cooler portions of the piston chamber 51 where it may reject the heat to the adjacent walls. During this alternate process of cooling oil movement between the hot crown zone and cooler skirt zone of the piston,

' changing directions of piston movement and the rapid changes in the acceleration thereof cause the body of the cooling oil retained in the piston skirt chamber to slosh back and forth between the hot and cooler zones of the piston with a turbu- Jent and rapidly flowing action which greatly enhances the rate of heat transfer to this cooling medium. The volume of .cooling oil retained in the piston and that which has been found to produce the best cooling eflect is equal substantially to one-half of the total volume of the chambered area defined between the piston body and the insert. Therefore, the over fiow ports 68 are located at a zone such that this optimum volume of oil is trapped in the piston skirt chamber 61.

This assures the presence of some cooling medium during the engine starting periods when the supply from the engine is building up to its normal pressure. Thereafter, the rate of supply at port 62 will be compensated by the over flow at ports $8 to maintain the desired volume in the chambered areas of the piston.

Considering, now, the structural features and advantages of the present improvements, it can be appreciated that the thrust loads on the piston crown ii will be absorbed by the strut members 51 and i 9 and passed into the upper face 38 of the insert for distribution throughout the latter and into the connecting rod with a minimum of highly stressed areas. The lateral thrust or side loads on the piston body are principally concentrated at the annular zones or bands defined by the thickened upper ring boss l6 and the similarly thickened lower ringboss 28 of the skirt. These loads are then transmitted to the insert body 35 over the large bearing areas of the spaced projections 31 seated against the surface 26, and at the flanged surface 43 fitting the skirt wall 3i. It is further to be noted, that in the axial assembly of the insert and piston, the axially directed securing studs 64 act only in tension and distribute such tension forces between the bottom of the insert body 35 and the thickened upper piston ring boss it and adjacent webs 23. Considered together the structural characteristics of the present piston and insert assembly relieve the piston crown portions of all but the necessary axial loads incident to the forces produced upon combustion of the fuel.

As a consequence of this preferred construction, the spherically convex crown i3 and the adjacent annular concavo-convex crown wall it are free to expand and flex with the rise of temperature on the combustion side, and are not restrained in any manner by the axial and side loads or forces created as an incident to normal piston reciprication and accompanying oscillatory movement of the connecting rod. With a plSton crown configuration having the gradually curved areas shown in Figs. 2 and 3, it will be possible to maintain the critically stressed zones so substantially below the rupture stress values as to preclude crown wall failure normally caused by fatigue and constriction thereof. The concave wall It and concavo-convex wall it of the piston crown are admirably suited to the necessary flexing during operation of the piston without concentrating stresses at any particular point or zone.

The above description given in connection with the accompanying drawing is characteristic of the presently preferred piston construction, but it is to be understood that certain changes and modifications may be made herein without materially departing from the spirit and intended scope of the annexed claims.

What is claimed is:

1. In a piston, a body having a crown and a ;kirt portion, said crown portion being formed with a central area of spherically convex form and an adjacent peripheral area of concavo-convex form integrally united at its outer margin with said skirt portion, an inner and outer series of strut members integrally formed with and depending from said crown portion, the strut members of the outer series being staggered relative to the inner series and being connected with said skirt portion at a zone below the concavo-convex area of said crown portion, whereby the said areas of the crown portion are unrestrainedly free to expand, contract and flex as a result of the thermal and mechanical forces incident to piston operation, and an insert member disposed in said body, to bear against said skirt portion at axially spaced zones and to contact said strut members,

L said insert member having a recess opening inwardly of said inner series of strut members and through which a cooling fluid may enter the crown portion of the body for flow across the said crown areas and between and around said inner and outer series of strut members to carry off the heat imparted thereto during piston operation.

2. In a piston, a body having a crown portion and a skirt portion, said crown portion being formed with a spherically convex central area and a concavo-convex peripheral area extending axially above the central area and integrally united with said skirt portion at its outer margin, a plurality of strut members, each of arcuate form in transverse section, formed on and depending from said crown portion, said strut members being arranged in an inner and outer series to provide slot-like ports therebetween, the ports of one series being angularly off-set relative to the ports of the other series, an insert member disposed in said body to bear at one end against said strut members, the opposite end of said insert having a sliding fit in the skirt portion whereby a skirt chamber is formed between the skirt and insert,

ports opening from the skirt chamber to the interior of said insert between the ends thereof, and

said insert having a recess opening toward the central area of said crown portion to direct a cooling fluid onto the convex area of said crown, said ofi-set strut ports directing the cooling fluid outwardly in radial and circumferential paths toward the concavo-convex area of said crown and into said skirt chamber, the cooling fluid retained in said skirt chamber in excess of that passing through said insert ports being dashed back and forth in said chamber and crown portion due to inertia forces incident to piston operation.

oi the volume of the skirt chamber and the space 3 in said body crown portion.

LOUIS E. ENDSLEY. WESLEY W. BCHE'I'ILER.

nnmnnncns orrm UNITED STATES PATENTS Number Name Date 2,046,196 Truxell, Jr., June 30, 1936 2,241,629 Brill May 13, 1941 JOHN HOWARD LENTELL. [a 2,879,359 Kettering June 26, 1945

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