US2400503A - Piston for internal-combustion engines - Google Patents

Description

May 21, 1946; w. HARPER, JR 5 PISTON FOR INTERNALCOMBUSTION ENGINES Filed Nov. 16, 194 5 Sheebs-Sheet 1 Mnswrw? #44109; $19265; Jk.

mm kbinand W YTI'ORNEYS May 21, 1946. J w. HARPER, JR 2,400,503 PISTON FOR INTERNAL-COMBUSTION ENGINES Filed Nov.. 16. 1942 5 Sheets-Sheet 2 INVENTOR 14 41/14 625F539, Z9.

55 BY wzmw TI'ORNEYS May 21, 1946. w. HARPER, JR 0 I PISTON FOR INTERNAL-COMBUSTION ENGINES Filed Nov. 16, 1942' 5 Sheets-Sheet 3 INVENTOR [fizz/4M Aha/v5.17:

BY -W1- W- A ORNEY5 May21, 1946. w; HARPER, JR

PISTON FOR INTERNAL-COMBUSTION ENGINES 5 Shets-Sheet 4 Filed No v. 16, 1942 ATTORN EYS y 1946. w. HARPER, JR ,503

PISTON FOR INTERNAL-COMBUSTION ENGINES Filed Nov. 16, 1942 5 Sheets-Sheet s 'I/II/l/ll/I Ill/Ill lI/I/l/iLl ATTORN EYS Patented May 21, 1946 William Harper, In, Montreal, Quebec, Canada Application 13 Claims.

This invention relates to pistons for internal combustion engines and the method of fabricating the same, and aims to provide a rugged piston of reduced weight and which will conduct heat rapidly to a cylinder wall.

It is well known that pistons for internal combustion engines, particularly those which operate at high speed, should be as light as possible to provide the minimum inertia in rapid reciprocation. It is necessary also that such pistons conduct heat rapidly from the head to the cylinder walls. The pistons which have been providedfor high-speed internal combustion engines in the past have been cast as complete units from a light metal of high heat conductivity such as aluminum. However, an undesirably high percentage of those castings prove to be defective. Furthermore, aluminum, although lighter and a better heat conductor than steel or iron, is possessed of serious disadvantages, the principal of which are its high coeflicient of thermal expansion, as compared with that of the iron cylinders for which the piston is designed, its weakness, as compared with that of steel, and its scarcity. Furthermore, the pistons of the past have required a heavy boss to serve as a. bearing for the wrist pin.

I have discovered that the former disadvantages may be overcome by fabricating a piston of separate parts including a head formed from a piece of metal which is comparatively massive so that it will conduct heat readily to the cylinder walls, and a skirt which may be of a thin sheet metal such as steel; and that the heavy wrist pin November 16, 1942, Serial No. 465,774

boss used in Past pistons may be eliminated and a 0 light tension member may be utilized to provide a housing for, the wrist pin bearing and a tie between that bearing and the skirt of the piston. The piston embodying my invention has a head composed of a comparatively massive piece of metal to which is attached a separate cylindrical skirt whose wall is composed of sheet metal of high tensile strength. Such a piston may be fabricated by wrapping a flat sheetof thin metal of high tensile strength around a cylindrical mandrel and welding its meeting edges to each other to form the skirt and then attaching an end of the skirt to a comparatively massive head formed from a separate piece of metal.

Other features of my invention will appear from a detailed description of the preferred embodiment illustrated in the accompanying drawings in which:

Fig. 1 is an axial section on a plane perpendicular to the wrist pin; 1

F18. 2 is an axial section on the plane containing the axis of the wrist pin;

Fig. 3 is a section along the lines 33 of Fig. 1;

'Fig. 4 is a section along the lines 4-4 of Fig. 1;

Fig. 5 is an exploded fragmentary section showing the piston head and the upper part of the skirt;

Fig. 6 is a fragmentary plan view of the means for attaching the skirt to the head;

Fig. 7 is a plan view of the tension member housing the wrist pin bearing, including a transverse section of the piston skirt to which the tension member is attached;

Fig. 8 is a plan view of the sheet of metal used to form the tension member housing the wrist pin bearing;

Fig. 9 is a plan view of the sheet of metal illustrated in Fig. 8 after it has been wrapped over a conical form;

Fig. 10 is a side view of the member illustrated in F18. 9;

Fig. 11 is an axial section on a plane perpendicular to the wrist pin of a modified piston;

Fig. 12 is an axial section on the plane containing the axis of the wrist pin of the piston illustrated in Fig. 11;

Fig. 13 is a section along the line l3--I3 of Fig. 11;

Fig. 14 is an end view of the wrist pin for the piston illustrated in Figs. 11 and 12;

Fig. 15 is a fragmentary section illustrating a mode of attaching the wrist pin bearing to its housing; and

Fig. 16 is a plan view of a, locking plate for the wrist pin bearing.

The piston illustrated in the drawings is particularly designed for use in an internal combustion engine of the type shown in my Patents No. 2,151,698 dated March 28, 1939, andNo. 2,272,171 datedFebruary 10, 1942, in which air is admitted to the cylinder from the crank case through ports in the piston skirt which are adapted to register with ports in the cylinder. It includes a comparatively massive head which is preferably formed from a metal such as aluminum which is a'good conductor of heat; a skirt whose wall consists of a cylinder whose outer circumference at normal temperatures is greater than that of the head, and which is composed of thin sheet metal, preferably sheet steel; and atension member, preferably of sheet steel also, which provides the housing for a wrist pin bearing and a tie between that bearing and the skirt.

In the piston illustrated in Figs. 1 to 10 of usual piston ring grooves 2!, below which the portion 22 is undercut to provide flange 23 and to receive the oval heads 24 of bolts 25 whose ends project through slots 26. Projecting from the inner surface of head it are fins 21. Y

The skirt is is formed by wrapping a thin sheet of metal of high tensile strength such as molybdenum alloy steel around a cylindrical mandrel and then welding the meeting edges at 29 to form cylindrical wall l6. In a piston whose diameter is approximately nine inches and which is subjected to pressures as high as 600 lbs. 'per square inch, the sheet of steel utilized for wall it may be in the neighborhood of one-eighth of an inch in thickness. It will be appreciated that the thickness of the sheet steel wall it may be decreased for smaller pistons or lower compression. An annular channel member 30 provided with bolt holes 3| is welded to the inner surface of wall It along its outer end.

The piston skirt I is also provided with ports 32 and longitudinal reinforcing struts 34 as follows: Longitudinal strips 35 are welded to inner wall It and slits are made in that wall so that the portions 36, 31 and 38 may be pushed inwardly to provide the openings constituting ports 32, and to cause the edges of portions 33 to meet the edges of portions 31, and the edges of portions 38 to meet the edge of strip 35, when the respective edges are welded at 39. The skirt II is also provided with annular trusses II and 42 located, respectively, at the inner ends of struts 34 and the inner end of skirt It.

The truss II is constructed of an annular sheet metal member 44 welded at I! and 43 to the annular sheet metal member 41 which in turn is welded to the inner surface of wall It. so that its outer surface abuts the inner ends of struts 34. The truss I2 is constructed in part from the cylindrical base 50 of tension member l1 which is welded to the inner surface of wall I i at its inner end. The balance of truss 42 consists of annular sheet metal member 5| welded to tension member l1 and to wall It.

The tension member i1 is formed from a sheet of malleable metal of high tensile strength such as a .30 to .40 carbon'steel alloy containing 2% to 3% nickel and some molybdenum which, forthe particular piston previously referred to, is of the order of three-sixteenths of an inch in thickness. in Fig. 8, is wrapped upon a cone-shaped form as illustrated in Figs. 9 and and the meeting edges 53, 54 are welded at 55, 53 respectively.

It will be noted that the apex of the form, illustrated by dotted lines in Fig. 10, has been removed to provide the rounded end which forms the housing 18 for the wrist pin bearing and which consists of a continuous sheet of metal containing no weld so that it is better able to withstand the very high stresses to which that apical end portion is subjected.

The conical tension member l1 so formed is then perforated to form ports 58 and the metal surrounding those perforations is forced inward to provide reinforcing flanges 53, and perforations are made at either side of the housing It to receive bolts 8|. The wrist pin bearing includes a threaded sleeve 02 for bolts ll and bronze bushings 33, 84 between which the bearing 85 of connecting rod 68 is mounted. The bronze bushing 33 is prevented from turning with the wrist pin bearing SI by means of flange member 83 which abuts against that bushing and is attached to the split plate 33. Fixed to ten- Such a sheet, of the shape illustrated sion member II are threaded tubes 1| for .bolts 12 which hold the plate 63 in place. Oil passages 13 are provided for the admission of lubricating oil to the bearing and the bushings 33,34.

The formed piston skir't, its reinforcements and the formed tension member are assembled; channel member 30, trusses ll, 42 and tension member I1 are spot welded in their proper positions in skirt l5. Those parts are then securely fixed in place, preferably by copper braising in a con-- trolled atmosphere at a temperature which is above the temperature for the heat treatment of the steel used in the assemblage. Stresses in the assemblage are relieved by heat treatment and the outside diameter of skirt I5 is then centrally ground. The skirt l5 may also, if desired, be cam ground in known manner to compensate for side thrusts during operation of the piston. I

The skirt I5 is preferably provided with an antifriction surface as follows: The outer surface is sandblasted to provide a mat finish and is then given a bonding surface of copper or spelter matrix. The bonding surface is then provided with a coating which is a few thousandths of an inch in thickness of an anti-friction metal such as babbitt by spraying such metal in a porous condition over the outer surface of the skirt. This coating not only has a lower coefficient of friction than the steel utilized in the skirt l5 but 'also, by virtue of its porosity. provides an oil The head M is then attached to skirt l5 by- 'means of bolts 25, which are prevented from falling out of slots .26 by snap ring 15 before they are inserted through holes-3| and nuts 16 held in proper position on bolts 25 by cotter pins 11. The nuts 13 should not be seated too tightly against channel member 30 but should be sufficiently loose to permit slippage between the contacting surfaces of head portion 22 and channel member 30 to permit independent radial expansion .by head I and skirt It.

In the modified form of piston which is illustrated in Figs. 11 to 16 inclusive, the wall It of the skirt I5 is formed from a hollow cylinder of sheet steel which is provided with ports 32' and wrench holes 19. The longitudinal reinforcing struts 34' are separately formed from sheet metal and are then mounted in a Jig and welded to annular sheet metal member 44' and to the member 30 which is provided with bolt holes 3| and with an upturned lip which is adapted to fit against the inner surface of the portion 22' of piston head H. After these parts are assembled, they are fitted within the cylindrical skirt It so that longitudinal struts 34 register with the metal between ports 32- and this assemblage is bonded together'as by means of copper braising.

The tension member I1 is similar to the tension member l1 except that it is provided with a peripheral flange which fits into the annular groove II at the inner end of skirt. l5 and to which it is bonded. If desired, compression membets '2 formed of sheet metal may,connect the inturned lip of annular member 30' with the ten sion member l1 to which they may be bonded.

The piston head It, as illustrated in Fig. 13, is provided with internal fins 21' which are curved in the direction of the flow of air through the ports 32' to decrease the resistance oil'ered to the flow of such air and permit a greater volume of air to flow past them and to relieve thermal stresses in those fins. The assembled skirt I is fastened to the piston head ll by means of bolts 25 which are screwed in threaded holes in the portion 22. It is to be noted that the heads of the bolts 25' are located within the hollow longitudinal struts 34' providing a rigid structure and preventing those heads from obstructing the fiow of air through the piston. The ends of the bolts 25 are provided with slots 84 to receive pins 85 inserted therein through holes 86 in the portion 22 ofthe piston head after the bolts have been seated in place. After pins 85 are inserted, they are held in place by the piston ring (not shown).

Means are provided, as illustrated in Figs. 12, 14 and 15, for preventing the wrist pin and wrist pin bearings from becoming displaced. A square key 88 fits in registering keyways provided for it in the threaded sleeve 62 and in tension member engine cylinder, thus preventing slapping or pumping of oil by the piston when the engine is cold. The aluminum head l4 (or head I4),

whose index of thermal expansion is greater than that of skirt i5 (or 'skirt I5), is permitted to expand by providing a clearance between the periphery of portion 22 (or portion 22) of the head and channel member 30' (or the member 30), and by making the holes for bolts 25 (or bolts 25') larger radially than the shanks of those bolts. ,The circumference of the head l4 (or head it) is reduced so that it will not seize thecylinder wall when it becomes hot and expands. As the piston is operated, the very high heat to which the comparativel massive head M (or head I4) is subjected is conveyed through piston rings to the cylinder wall, thus preventing the head from becoming excessively hot. Transfer of heat from the head is augmented by air flowing from the crank case through ports,58 (or ports 58') past fins 21 (or fins 21') and thence through ports 32 (or ports 32).

It will be noted that the thin sheet metal wall 18 or wall I8) of the piston skirt is internally reinforced circumferentially at each end and at a point intermediate its-ends, and is also-internally reinforced longitudinally; Consequently, that thin sheet metal wall may be subjected to the extremely high compressive forces encountered inthe operation of the piston without buck-J ling or collapse. The member I1 or member I1) is under tension during operation of the piston and, since thrusts between the piston skirt and the wrist pin are, by virtue of the conical shape of that tension member, transmitted along straight lines. it may be formed of light thin sheet metal without danger of failure. As a result, the piston which I have invented provides a very rugged construction of reduced Weight which will bear extremely heavy loads.

It is to be understood that the practice of my invention is not limited to the particular piston described above which is designed for use in an internal combustion engine having inlet ports in to said head.

the engine cylinder. Various features of my invention may be practiced in connection with pistons designed for valve-in-head engines, in which event ports 32 and. 58 (or ports 32' and 58') and fins 21 (or fins 21') may be dispensed with. Likewise, metals other than aluminum may be used in the piston head, and metals other than the steel referred to above may be used in the skirt of the piston without departing from the spirit of my invention as defined in the appended claims.

What I claim is:

1. A piston consisting of a head, a cylindrical skirt whose wall is composed of thin metal of high tensile strength and whose outer surface is provided with a porous coating of an anti-friction metal, and means for attaching the-skirt to said head.

2. A piston consisting of ahead composed of a comparatively massive piece of metal, a cylindrical skirt whose wall is composed of thin sheet metal, longitudinal struts fixed to said wall along its inner surface, and means for attaching the skirt to saidhead.

3. A piston consisting of a head composed of a comparatively massive piece of metal, a cylindrical skirt whose wall is composed of thin sheet metal and is provided with ports, longitudinal struts fixed to the inner surface of said wall along the edges of the ports, and means for attaching the skirt to said head.

4. A piston consisting of a head, a cylindrical skirt composed of thin sheet metal, an annular reinforcing member fixed to the inner wall of said skirt, longitudinal struts fixed to said skirt along its inner wall, and means for attaching the skirt 5. In a piston, the combination with a skirt and a wrist pin bearing, of a member fixed to the inner wall of the skirt along the major portion of a circumference of said skirt and providing a tie combination of a conical tension member whose base is fixed to the inner wall of the skirt, and a wrist pin bearing housed in the apex of said conical member.

8. In a piston having a head and a skirt, the combination of a conical tension member whose base is fixed to the inner wall of the skirt, a wrist pin bearing housed'in the apical end of said tension member, and a compression member connecting said conical member with said skirt.

9. In api'ston having a head, a skirt, and a ing ports therein, and fixed to the inner wallof the skirt, providing a tie between the skirtand said wrist pin bearing.

11. In a piston, the combination with a skirt and a wrist pin bearing, of a conical member having ports therein, and fixed to the inner wall of the skirt, providing a tie between the s irt and said wrist pin bearing, and reinforcing flanges surrounding said ports. a

12. A piston consisting of a head of aluminum, a cylindrical skirt whose wall is composed of sheet steel and whose circumference is greater than the circumference of said head at normal tempera tures, means for attaching one end of the skirt to said head to permit radial expansion bythe head and the skirt independently of each other,

a wrist pin bearing, and a conical tension mem- I ber composed of sheet steel whose apex houses the wrist pin bearing and whose base is fixed to the inner wall along the other end of said skirt.

13. A piston consisting of a head of aluminum,

' venting collapse of said skirt under compressive forces.-

WILLIAM HARPER, JR.

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