US3136306A

US3136306A - Piston for a high performance internal combustion engine

Info

Publication number: US3136306A
Application number: US104322A
Authority: US
Inventors: Wunibald I E Kamm
Original assignee: Stevens Institute of Technology
Current assignee: Stevens Institute of Technology
Priority date: 1961-04-20
Filing date: 1961-04-20
Publication date: 1964-06-09
Anticipated expiration: 1981-06-09

Description

W. l. E. KAMM June 9, 1964 PISTON FOR A HIGH PERFORMANCE INTERNAL COMBUSTION ENGINE Filed April 20, 1961 2 Sheets-Sheet 1 INVENTOR. WUIVIBALD LE. KAMM FIC .22; p z'ff m 14770 NEYS.

June 9, 1964 w. l. E. KAMM 3,136,306

PISTON FOR A HIGH PERFORMANCE INTERNAL COMBUSTION ENGINE Filed April 20, 1961 2 Sheets-Sheet 2 'WM- "J 44 I 40 INVENTOR.

WUN/BALD I. E. KAMM United States Patent This invention relates to improvements inpistons for internal combustion engines, and more particularly to an improved piston especially suited for high temperature, high pressure engines where torques of up to four times above those developed in ordinary engines are encountered.

Under such operating conditions, conventionally designed pistons are unable to withstand the increased pressures and temperatures of operation. As the torque is increased the mean effective pressure developed within the cylinder is proportionately increased and the heat developed within the firing chamber increases to such a point that conventional pistons would fail. The flow of such a large amount of heat through the piston top, the piston walls and over the piston rings to the cylinder walls would require such a large temperature gradient between the heat receiving surface of the piston and the cooled outside cylinder wall that the temperature level at the hotspotswould \exceed the limits that could be tolerated by the lubricating oil, the surface of the'piston, the rings and the cylinder walls. p

Pistons of conventional design, as regards the forces applied to the piston-pin which connects the piston to the connecting-rod, and the lateral pressure between the piston andcylinder walls, are already operated near their tolerable limits and cannot withstand pressure increases "up to four times above normal. 'One feature of my invention is a novel piston crown member secured to the upper end of the piston, which I have found will permit operation at such elevated temperature. and provide a wide margin of safety. The crown comprises a thin base plate which supportsa heat reflecting member contained in a thin hollow cylindrical cover. This construction, as will be described in detail fhereinafterfincludes an'oil' pumping arrangement which operateson each power stroke to deliver fresh oil to the outer surface of the piston for lubricating and cooling the sliding surfaces.

Another feature of my invention is the use' of a con-h meeting-rod having an integral cross-pin which provides 'a much greater bearing surface area than the conventional arrangement and thus gives rise to a better distribution of theseincreased drivingforcesr I 7' d A further featureis that I construct my piston body of two symmetrical half cylinders, which permits installation of the connecting-rod member and facilitates machining of the internal cavities of the piston member. .The two halvesof the piston body are connected together by a novel-tie-bolt arrangement passing [through the center ,of the connecting-rod pin.

These and other features of my invention'willnow be describedin reference to.the drawings illustrating a preferred. embodimentand in which: j FIG. '1 is a longitudinal sectional view of the piston andcrown assembly taken along a plane passing through theiaxis of the connecting-rod pin; 1

FIG. 2 is-aview -on=line:22 of FIG. 1, showing the .innerface of one of the two pistonsections with the crown member in position to illustrate the details ofthe oil circulation and lubrication system; and i Q t FIG.i3 is a horizontal cross-sectional view of the piston 3,136,306 Patented June 9, 1964 "ice In the drawings, the body 1 of the piston is of cast,

forged or pressed aluminum alloy or of cast or forged iron. The piston body 1 is constructed of two

symmetrical portions

34 and 35, each having a semi-circular crosssection. FIG. 2 shows the inner surface of one of these two portions 35 to illustrate the interior arrangement of oil ducts to be described later, FIG. 1 being a longitudi nal sectional view of the assembled halves taken on a plane passing through the axisof the connecting-rod pin. The piston body 1 is equipped with conventional piston rings 2 and, if desired, one or more oil rings 3 fitted into channels machined into the finished body.

The outer end of the piston body iscapped by a heat resistant hollow cylindrical crown member 4 which is made of heat resistant material such as chromium alloy steel, and it is attached-by screw threads 17 to an upwardly extending portion of plate 5. The parts 4 and 5 may be tightly interconnected by applying a spanner wrench to crown lugs 13 formed integral with the crown 4, which lugs are later removed by machining, or recesses 14 may be machined into the crown to receive lugs of a pronged spanner wrench. Plate 5 is a dual purpose member in loaded by a biasing element in the form of a spiral spring.

washer 22 to permit' slight axial movement of the members arising from thermal expansion, or from the explosive impact during firingv v The outer surface of the crown 4 is fitted with solid,

not split,

piston rings

7 and 8 which prevent the cornbustion gases of excessive pressure and tempertaure from reaching the piston body. A spacer ring 10 separates the two rings -7 and 8. The small clearanceprovided between the

crown rings

7 and 8 and the crown itself is such that there is little heat conduction directly from the crown to the ring. The gas pressure passing the upper land of the crown to the inner side of ring'7 acts radially outward, expanding to a predetermined degree this elastic ring, while pressing downwardly on the rings upper shoulder. This prevents the gases from passing down between ring 7 and the cylinder'wall and between ring 8 and the insert ltl.

Rings

7 and 8 are normally in running contact with the cylinder wall but, when expanded by the gas pressure, the contact pressure of'these rings against the cylinder wall is increased. By virtue of this contact with the cylinder wall, radiant heat from the crown 4 is conducted'directly to the cylindrical wall which, in turn, is

cooled externally byany of the well-known means of liquid or forced air cooling. The sealing action of ring 7 creates a large gas pressure drop in the running clearthe alloys are selected with proper consideration for. the

mean temperature differences of the two parts during the cooling process. f In high performance engines of'this general type, that reduces the available bearing surface.

mentjon the other hand, the upper bearing'surface of the a 3 portion of the head of the piston directly in line with the combustion flame is subjected to momentary periodic temperatures above 4000 F. This spot is generally located at the geometric center of the piston head. To protect the piston crown member from these destructive temperatures, I have provided the top surface of the crown with an insert 12 of heat-resistant material having a low heat conductivity factor. Suitable material for the insert 12 is ceramic material such as aluminum oxide. An annular member 11, also of the .same low heat conductivity material, is positioned beneath the insert 12 and rests in an annular recess in the upper surface of a heat radiation shield91. The latter is supported by an annular upwardly extending flange of they plate 5, this flange surrounding a recess for nut 6a. The insert element 12 restricts heat transfer by conduction between the crown 4 and the heat reflector 9, which is of highly polished low heat conductivity material. The ceramic inserts 11 and 12 and the heat reflector 9 arernaintained in position by the compressive relationship between the crown 4 and the plate 5. I

During operation of the engine, only a small portion of the heat developed at the top of the piston crown may reach the piston body l by direct conduction. This is because the conductive path from the head .of the crown is through the thin skirt 16, which inserts a high thermal resistance in the transfer path, to the lower plate 5 via the screw threads 17 (whichalso present a transition resistance) and from plate 5 to the piston 1 via the outer annular fiange of plate 5 where the parts meet, and also via the central portions 1% and 20 of plate Sand bolt 6 where they come into contact with the body of the piston. If desired, bolt 6 can be made hollow to reduce heat conduction through it. Heat transfer from the head 23 of the crown 4 by radiation to the lower inside skirt portion 16 of the crown, to the plate 5 and to the end of the bolt 6 and its respective nut, are greatly reduced by the inserted heat reflector 9. The heat reflector 9 may be a single body as shown, or it may comprise two or more axially space plates to improve its reflection efficiency.

The arrangement shown is highly efiicient and it has been proven byexperiment that not more than 1% of the heat, released in the cylinder by fuel burned in the com bastion chamber above the crown, reaches the body 1 of the piston, and also it has been'determinedthat plate 5 assumes an equilibrium temperature quite close to that of the body 1. 1

The piston body 1 is of unique design in that it is constructed in two

halves

34 and 35 which are united into one unit by a bolt 38 passing through the center of the piston-pinportion of connecting-rod 32. In high performance engines of the type operating at about four times the normal mean effective pressure, the conventional connecting-rod and piston-pin arrangement does not present sutiicient bearing surface towithstand the increased loading force's. Y

In FIG. 1 the novel arrangement of theconnecting-rod This configuration results in a bearing arrangement well able to withstand driving forces greatly in excess of conventional systems. The lower bearing surface of the cross-pin 31 does not carry the increased load and therefore need not exceed, in area, the conventional design.

As was previouslystated, the piston body is made from two

portions

34 and 35, each having a semi-circular cross-section; A view ofthe inner surface of one of these portions is shown in FIG. 2. One of the piston halves is fitted with locating pins 39 while the mating half, not illustrated, is fitted with corresponding recesses to prevent lengthwise separation of the portions during assemblyor operation. Each piston section is machined, in accordance with FIG. 2, to have a cavity 27 for receiving the head of the bolt 6 and to function as an oil circulation cavity for cooling and lubricating the piston body. There is an oil duct 42 leading upward from cavity 27 to the head of the body 1 which includes an enlarged cavity 26 enclosing a check valve disc 43. The body 1 also includes duct 24 slopping downward from the head of the body and having horizontal .branches 25 leading to the outer surface of the body directly beneath the respective piston rings 2.

Oil is introduced into the piston, under pressure, through duct 28 in the connecting-rod 32 and thence into the space 44 within the cross-pin 31. The oil then travels out through the duct 29 in the cross-pin (FIG. 2) to the cavity 27 via duct 30. The oil travels from cavity 27 through duct 42, check valve 43 and cavity 26 to the.

space 21 between the head of the piston body and the bottom of the crown base plateS. Thesurplus oil is then conducted from space 21 through the sloping duct 24 to the horizontal ducts 25 just below each of the piston rings 2.

' During operation of the engine, the inner part 20 of crown base plate 5, being of thin metal, forming a'resilient diaphragm, is deflected downwardly, in oil-can fashion, upon each explosion in the cylinder at the start of the'power stroke. At this instant the oil duct 29 in the cross-pin 31 is out of alignment with oil duct 30 in piston body 1 (FIG. 2), thereby sealing off the oil reservoir cavity 27, and the check valve 43 is seated to prevent passage of.oil back. to the cavity 27 from the space 21 between the crown and piston head., Thus, the downward deflection of plate 5, acting on the surplus oil in the space 21, forces oil from the ducts 25 onto the cylinder wall directly ahead of the piston rings 2 of the piston to provide an oil cushion between the moving parts. When the explosive force on the crown subsides, the base plate 5 returns to its normal or uncleflected position due to its own internal elastic spring action. During the restoration of plate 5 to its original shape and posi tion, it reduce the pressure in space 21 and acts to draw 32 is shown having an integral wrist pin 31 formed thereon, which pin extends transversely of the rod and is slightly shorter in length than the diameter of the piston. In

generally formed with an enlarged transverse ring por-' tion, or eye, through which a separate pin is passed. In the conventional design the upper bearing surfac'eof the piston must be cut away at the center to allow'for movement of the enlarged end of the connecting rod which In my arrangepiston body 1 is continuous and unbroken savefor a small oil duct 30, to be discussed later. I have also shaped the outerends of the cross-pin or wrist pin 31 to conform to the surface. contour of the piston 11, as shown at 36 of oil into this space from reservoir 27 by way of check .valve 43. V I The two sections 34--35 of the piston body 1 are secured together at the top by the compressive action of the downwardly-extending internally-beveled flange 18 of the lower crown plate 5 on the upper'externally-beV- .eled edge of the piston body 1, as caused by the securing means 6'6a. To insure that the piston body is held securely in one piece, a double-headed bolt 38 is passed through the hollow center 44,01? the piston-pin'31. As

'shownin FIG. 1, both ends of the bolt 38 are threaded,

outer surfaces to conform-to the cylindrical surface of FIG. 1 and by the dotted line 37 of FIG. 3, to increase i the piston, as may be seen in FIG. 3. The enlarged end portions of the tie-bolt 38 have centrally located countersunk splined socket holes 41 to receive a splined wrench. These keyways or socket holes could equally well be in the form of Allen Head, Bristo-Head or other wellknown type of socket shape.

As stated above, the threads of the ends of the tiebolt 38 differ in pitch but have identical thread direction, that is, both right-hand or both left-hand threads. If the original machining is accurately performed and if the nuts 40 are held in the correct position for engaging the threads, bolt 38 will be in the correct axial position on each reassembly of the parts, and the nuts will be properly oriented in the surface of the piston. The nuts 40 could be countersunk slightly at the surface of the piston if it is so desired.

It will be apparent that the thin part 20 of crown plate is spring loaded by the' spring washer 22 surrounding the hollow extension 19, this spring washer being compressed between the head of the connecting means or bolt 6 and an overlying internal shoulder of piston body 1. Consequently, the crown 4-5 continues to be held securely in position on piston body 1 even when the thin part 20 is deflected downwardly under the explosion impact (through flange 15), as previously described.

The duct or channel 28 in piston connecting-rod 32 may be supplied with oil from the usual high pressure lubricating system (not shown) of the engine, as through a passage at the inner end of rod 32 communicating with an oil supply under pressure in the crank housing. The outer passage 29 in the rod and the admission passage 30 to cavity 27 can be positioned so that the oscillating motion of the rod provides for oil admission during the upward stroke of the piston but seals channel 28 in the center-point (FIG. 2) and downward phase of the motion during which the check valve 43 is held seated by the pumping action of plate 5 incident to its downwarddefiection. However, a duplicate of the channeling 24-25 can also be arranged at the opposite side of the piston, either when the engine is reversible and high gas pressures act at the opposite angle of the connecting rod 32, or when the gas pressures during the compression stroke are so high that such extra lubrication of the piston is desirable or necessary. In this case, oil passages 29-30 may be arranged for oil admission at the greater rod angles of piston positions nearer the outer center-point where low gas pressures prevail.

I claim:

1. A heat butfer crown for a piston for high temperature internal combustion engines, which comprises a base member, said base member being adapted to physically contact the piston over only a minor portion of its surface to minimize heat transfer by conduction, means for interconnecting said base member and the piston, a heat reflecting element supported by said base member, a heat insulating element supported by said heat reflecting element, and a hollow cylindrical cover enclosing said elements and releasably connected to said base member.

2. A heat buffer crown as in claim 1, wherein the interconnecting means include a yieldable biasing element operable to urge the crown against the piston.

3. A heat buffer crown as in claim 1, wherein the cover has a cylindrical skirt portion having a peripheral recess therein, and an endless sealing ring disposed within said recess.

4. A heat buffer crown for a piston forhigh temperature internal combustion engines, which comprises a hollow cylindrical body having opposite deflectable end walls and a cylindrical side wall, one of said end walls having a flexible diaphragm portion and a peripheral spacing flange engagable with the piston to hold said diaphragm portion in spaced relation to the piston, means extending centrally from said diaphragm portion for securing said body to the piston, and displaceable'means disposed in said body and through which said diaphragm portion is deflectable by deflection of the opposite end wall.

5. A heat buffer crown according to claim 4, in which said. displaceable means include a heat reflecting element.

6. A heat butfer crown according to claim 4, in which said displaceable means include a heat insulating element. 7. A heat buffer crown according to claim 4, in which said displaceable means include heat reflecting and heat insulating elements.

8. A heat buffer crown according to claim 4, in which said cylindrical side wall has an external circumferential recess, the crown comprising also a sealing ring in said recess. a

9. A heat buffer crown according to claim 4, in which said opposite end wall has a skirt forming said side wall, the skirt having a threaded connection with saidone end wall at the region of said peripheral flange.

10. A heat buffer crown according to claim 4, in which said opposite end wall has a skirt forming said side wall, the skirt having a threaded connection with said one end wall at the region of said peripheral flange, saidskirt also having an external circumferential recess, the crown comprising also a sealing ring in said recess. p

11. A piston assembly for high compression internal combustion engines, which comprises a piston body, said piston body including two semi-cylindrical sections, a connecting rod at one end of said body pivotally connected thereto and having a hollow wrist pin rotatably disposed within cylindrical bearing cavities of both piston sections, a transverse tie-bolt having threaded end portions disposed to pass through said hollow wrist pin, and locking nuts on said threaded end portions holding said body sections together, the hollow of the wrist pin form ing an annular chamber around the bolt, the ends of said chamber being closed by the nuts, the piston body having an oil channel leading from the wrist pinfor delivering lubricating oil to the side wall of the assembly, the connecting rod having an oil supply passage leading to said chamber, and the wrist pin having a passage positioned to communicate with said channel in a predetermined angular position of the rod relative to the piston body.

12. A piston assembly for high temperature internal combustion engines which comprises a cylindrical piston body adapted for connection at one end to a connecting rod, a cylindrical heat buflfer crown at the other end of said body, said crown including a hollow cylindrical member, said crown and said body being in heat conducting contact with each other over only a minor portion of their contiguous surfaces, whereby heat conduction between said crown and body is minimized, connecting means securing said crown and body together and a highly polished low heat conductive heat reflecting shield mounted in said hollow cylindrical member and extending generally transversely of the piston body.

13. A piston assembly for high temperature internal combustion engines which comprises a cylindrical piston body adapted for connection at one end to a connecting rod, a cylindrical heat buffer crown at the other end of said body, said crown and body having interengaging peripheral surfaces and spaced opposing surfaces extending radially inward from said' peripheral surfaces to define a space, and connecting means disposed centrally of the piston assembly and surrounded by said space for securing the crown and piston body together at said peripheral surfaces, in which said connecting means include a yieldable biasing element urging said peripheral surfaces together to accommodate different thermal expansions of different parts of the assembly.

14. A piston assembly for high temperature internal combustion engines which comprises a cylindrical piston body adapted for connection at one end to a connecting rod, a cylindrical heat buffer crown at the other end of said body, said crown and body having interengaging peripheral surfaces and spaced opposing surfaces extend-' ing radially-inward from said' peripheral surfaces to define a space, and connecting means disposed centrally of the piston assembly and surrounded by said spacefor securing the crown and piston body together at said peripheral surfaces, in which the piston body includes 7 two longitudinal sections, said interengaging peripheral surfaces including a bevelled internal surface of the crown and a bevelled external surface of the body surrounding said internal surface, whereby said sections are held together by the connecting means through said bevelled surfaces.

.15. A piston assembly for high temperature internal combustion engines which comprises a cylindrical piston body adapted for connection at one end to a connecting rod, a cylindrical heat buffer crown at the other end of said body, said crown and body having interengaging peripheral surfaces and spaced opposing surfaces extending radially inward from said peripheral surfaces to define a space, and connecting means disposed centrally of the piston assembly and surrounded by said space for securing the crown and piston body together at said peripheral surfaces, in which the crown includes a resilient plate diaphragm partly defining said space and adapted to flex toward said body under an explosion impact transmitted through the crown from the end thereof remote from said body, said body having an oil receiving cavity and a passage leading from said cavity to said space, the assembly comprising also a check valve in said passage to prevent flow from said space to the cavity, the assembly having an oil discharge passage leading from said space through the side wall of the piston assembly, whereby the diaphragm is operable by said flexing to force oil from the space through said discharge passage and to draw oil from the cavity into said space upon return movement of the diaphragm away from said body.

16. A piston assembly for high temperature internal combustion engines which comprises a cylindrical piston body adapted for connection at one end to a connecting rod, a cylindrical heat-bullet crown at the other end of said body, said crown and body havinginterengaging peripheral surfaces and spaced opposing surfaces extending radially inward from said peripheral surfaces to define a space, and connecting means disposed centrally of the piston assembly and surrounded by said space for securing the crown and piston body together at said peripheral surfaces, in which piston assembly the crown includes a resilient plate diaphragm partly defining said space andadapted to flex toward said body under an explosion impact transmitted through the crown from the end thereof remote from said body, said body having an oil-receiving cavity and a passage leading from said cavity to said space, the assembly comprising also a checkvalve in said passage to prevent flow from said space to the cavity, the assembly having an oil discharge passage leading from said space through the side wall of the piston assembly, whereby the diaphragm is operable by said flexing to force oil from the space through said discharge passage and to draw oil from the cavity into said space upon return movement of the diaphragm away from said body.

References Cited in the file of this patent UNITEDSTATES PATENTS 1,225,401 Blanchard May 8, 1917 1,547,687 Rohwer July 28, 1925 2,214,891 Schron Sept. 17, 1940 2,360,642 Berg Oct. 17, 1944 2,446,348 Webster Aug. 3, 1948 2,569,103 Huber et a1. Sept. 25, 1951 2,720,871 Morris Oct; 18, 1955 2,742,883 Smith Apr. 24, 1956 2,782,083 Hewson Feb. 19, 1957 2,807,247 Cramer Sept. 24, 1957 2,835,542 Holstein May 20, 1958 FOREIGN PATENTS 949,304 France d. Feb. 14, 1949

Claims

1. A HEAT BUFFER CROWN FOR A PISTON FOR HIGH TEMPERATURE INTERNAL COMBUSTION ENGINES, WHICH COMPRISES A BASE MEMBER, SAID BASE MEMBER BEING ADAPTED TO PHYSICALLY CONTACT THE PISTON OVER ONLY A MINOR PORTION OF ITS SURFACE TO MINIMIZE HEAT TRANSFER BY CONDUCTION, MEANS FOR INTERCONNECTING SAID BASE MEMBER AND THE PISTON, A HEAT REFLECTING ELEMENT SUPPORTED BY SAID BASE MEMBER, A HEAT INSULATING ELEMENT SUPPORTED BY SAID HEAT REFLECTING ELEMENT, AND A HOLLOW CYLINDRICAL COVER ENCLOSING SAID ELEMENTS AND RELEASABLY CONNECTED TO SAID BASE MEMBER.