US2130923A - Piston land construction - Google Patents

Description

F. JARDINE PISTON LAND CONSTRUCTION Sept. 20, 1938.

Filed April 16, 1936 lhwentor F'EA/VK JARED/IVE fig r (Ittornegs Patented Sept. 20, 1938 PATENT OFFICE PISTON LAND CONSTRUCTION Jardine, Cleveland, Ohio, assignor, by mesne assignments, to Cleveland Trust Compuny, Cleveland, Ohio, a corporation'of Ohio,

trustee Application April 1a, 1936, Serial No. 74,736

18 Claims. (01. 309-10) This invention relates to pistons for internal combustion engines, and more particularly to an improved ring land construction for internal com- 7 cross head and includes a head havinga cylinthe cylinder without binding atall temperatures drical flange grooved on the outside to receive packing rings, bosses to support the wrist pin to join the piston tothe connectingrod, and a skirt which has surfaces arranged to slide upon the cylinder walls to guide the piston in its reciprocation. v

, Pistons composed of light metal such as aluminum alloys and the like for operation in cast iron cylinders have many recognized advantages in internal combustion engines. Aluminum and other light metal alloys, however, have a sub-- stantially higher coeflicient of expansion than cast iron. Accordingly, in order to obtain skirt bearing surfaces which will freely slide within encountered in operation, and which have a sumciently close lit at low operating temperatures to prevent the piston from slapping back and forth in the cylinder, it has been necessary to provide some means for compensating for the excess thermal expansion of the piston within the cylinder.

The most widely used constructions for compensating for the excess thermal expansion of a light metal piston skirt have been those in which the skirt is made yieldable so that when the piston is cold it may be fit fairly closely, at least at certain points, and will yield to avoid binding or excess friction when the piston is hot. One of these is the split skirt piston in which one or more substantially vertically extending slots are cut through the height of the skirt. The most successful yleldable skirt construction which has heretofore been used is the T-slot piston such as illustrated in the patent to Moore, No. 1,927,611.

The clearancesleft between the surfaces of the ring lands and the walls of the cylinder in the conventional piston constructions have been great enough so that at the maximum operating temperature the excess expansion of the piston head will not bring the lands into engagement with the cylinder wall, .and also great enough to prevent contact between the ring lands and the cylinder wall upon bodily movement of the piston within the cylinder resulting from yielding of the skirt under the lateral thrusts to which the piston is subjected during reciprocation.

As a result the piston is guided in the cylinder only by the skirt, the ring flange of the head serving to carry the piston packing rings and, in most constructions, to connect the head with the wrist pin bosses and the skirt. In the type of piston having a yieldable skirt to accommodate the excess expansion of the light metal alloy it will be apparent that the head is maintained centered within the cylinder by the skirt, which is a yieldable support. During the normal operation of a conventional Otto cycle internal combustion engine with connecting rods, or pitmen, connecting the piston to the crankshaft, there are six reversals of the direction of thrust of the piston against the cylinder walls during each complete cycle, or each two revolutions of the crankshaft. One reversal occurs at each end of each stroke and likewise reversals occur at the point in the intake and exhaust strokes where the acceleration of the piston changes to deceleration. At each reversal of the direction of thrust a tendency exists for the piston head, due to its inertia, to swing towards one side or the other of the cylinder aboutits yieldable support by the piston skirt. Similarly other forces exerted upon the pistontend to cause the piston head to tilt one way or another towards the walls of the cylinder.-

Illting of the piston head within the cylinder results in excessive oil consumption It is uncertain exactly why the tilting of the piston even an extremely slight amount causes excessive oil consumption, but according to one theory the edges of the piston packing rings which engage' the oil film upon the surface of the cylinder when the head and the rings are tilted act to break the continuity of the oil film which permits the oil to escape from the cylinder wall and be burned in the combustion chamber.

According to anoth'er'theory the tilting of the packing rings creates wedge shaped spaces between the bearing surfaces of the rings and the cylinder wall which squirt oil upwardly into the combustion chamber. It has also been suggested that when the rings are tilted their edges serve to scrape oil on the upward strokes and that during the explosion the spacing of the upper edge of the ring from the cylinder wall on one side may permit combustion between-the ring and the cylinder wall resulting in burning of small quantities of oil. In addition when the oil film is broken excessive friction is developed between the piston and the cylinder wall resulting in localized high temperature which burns oil upon the bearing surfaces. Some or all of these phenomena may occur when the piston head tilts or rocks within the cylinder, resulting in oil waste. It will be observed that if as much as one eighteen-millionth of a gallon of oil is wasted or consumed by each piston in each cycle in an average six cylinder automobile engine, a gallon of oil will be consumed or wasted during each thousand miles that the automobile travels. It is therefore difficult to determine exactly why tilting or cooking of a piston causes excessive oil consumption, or the exact operation by which the present invention cures such excessive consumption.

According to the present invention the piston head is so constructed as to bear upon the cylinder walls and prevent the head from tilting or rocking with respect to the skirt or cylinder to thereby prevent any head slap and likewise maintain the cylindrical bearing surfaces of the packing rings inaccurate alignmentwith the cylinder walls. More specifically the present invention provides an arrangement whereby sufflcient bearing is obtained between the piston head and thecylinder wall to prevent tilting of the piston while at the same time provision is made for the excess thermal expansion of light metal piston alloys so that the piston may reciprocate freely within the cylinder at all operating temperatures without danger of binding, scoring or excessive friction.

In addition the present invention includes a light metal alloy piston having a yieldable skirt of any type designed for operation in an engine cylinder composed of cast iron or the like and a ring flange upon apiston head having portions arranged to bear upon the cylinder walls to prevent tilting or rocking of the piston.

A piston according to this invention is preferably constructed with ring lands ground oval in cross section with the major axis of the oval perpendicular to the wrist pin axis and with a clearance at the ends of the major axis such that when the skirt yields under a lateral thrust and the piston thereby moves laterally within the cylinder, one end of the major axis of the,ring lands comes into engagement with the cylinder wall, thereby preventing further movement of the piston head and consequent tilting within the cylinder. ring lands the circumferential length which may move into engagement with the cylinder wall islimited and the friction is thereby limited. The ring lands may also be constructed to engage the cylinderwall through only a part of their height to further limit the area in engagement and the friction. When the piston reaches its maximum operating temperature the portions of the ring lands at the ends of the major axis are By reason of the oval contour of the of the light metal piston alloys. Oil consumption is reduced to aminimum without the use of special packing rings and without excessive friction within the cylinder. Likewise all danger of head slap from rocking or swaying of the head with respect to the skirt is eliminated.

Further advantages relating to simplicity of construction and economies in manufacture will appear from thefollowing description and the attached'drawing wherein:

Figure 1 is an elevation with parts in section of a piston constructed according to my invention;

Figure 2 is a plan view looking down on'the piston and cylinder assembly of Figure 1;

Figure .3 is an elevation on an enlarged scale of one formof ring land construction;

Figure 4 is a view similar to Figure 3 illustrating a modified land construction;

Figure 5 is a view similar to Figures 3 and 4 and illustrates a furthermodification; and

Figure 6 is a view corresponding to Figure 2 illustrating a modified land contour.

Generally speaking, I have attained certain objects and avoided many disadvantages in piston lan'd construction above referred'to by increasing the diameter of the piston head or land portion across the thrust face axis, and by maintaining the normal clearance across the piston pin axis, or in some instances, actually increas-' ing the clearance between the piston head and the cylinder wall across the wrist pin axis. Preferably the contour of the head portion of the piston is obtained by machining the piston head I to provide the same with an oval cross sectional contour, wherein the major axis of the oval as at B (Figure 2) coincides with the thrust face axis of the piston and the minor axis of. the oval as at C coincides with the wrist pin axis ofthe piston. The primary result of decreasing the clearance between the piston head and the cylinder Wall across the thrust face axis is to permit the ring lands in that portion of the piston to bear against the cylinder wall and serve as a guide to prevent tilting of the piston and thereby restrict the piston to a truly vertical reciprocation within the cylinder.

The diameter across the thrust face axis in the head portion of a piston constructed according to my invention is less than the diameter across the same axis in the skirt portion, and referring to the drawing in Figure 1 I have shown a piston arranged within a cylinder with the piston head 5 and the land portions 6, I, 8 and 9 bearing against the cylinder wall at one side of the piston. Since the diameter across the thrust face axis B in the skirt portion I0 is greater than across the same diameter in the head portion, this position of the piston requires that the thrust face H be fiexed somewhat, and I have indicated this fiexing on an exaggerated scale by the dotted line i la. In other words, in the absence of anyfiexingor yielding in the skirt portion, the skirt H would bepositioned as at Ma, and thus prevent the lands 6 to 9 from hearing on the cylinder wall. The condition illustrated in Figure 1 therefore assumes that a force is acting laterally of the piston in the direction of the arrow A.

With normal or conventional clearances in the skirt andhead portions, flexing of the skirt or tilting of the piston to bring the ring lands into engagement with the cylinder as shown in Figure 1 would produce a noise or slap. According to my invention, however, the diameter of the head portion across the thrust face axis B with respect to the skirt portion across the same axis is such that the permitted amount of movement of the piston head is less than the movement necessary to produce an audible slap. Since both the head and skirt engage the cylinder wall no tilting of the piston can take place. The movements of the piston throughout its cycle of operation, therefore, are substantially straight vertical reciprocations.

As an illustration of the relative dimensions that may be used in practicing my invention I have found that in constructing what is known as a three inch piston", the skirt may be machined to have a diameter across the thrust faces of 2.998 inches, and that the head portion or piston land constructed according to my invention may be machined to, have a diameter of 2.994 inches. Those skilled in the art. will readily appreciate that with a conventional or round cross section piston land, such clearances would be impossible, and that such standard or conventional round head would score and seize. I have found by test that a piston constructed according to my invention and having the clearances as above pointed out operated successfully withoutout any drag or scoring or seizing.

Inpistons constructed in accordance with the present invention, as in the conventional pistons of the prior art, the temperature of the piston head, and therefore the necessary amount of clearance, varies considerably with the conditions of service of the piston such as the average heat of combustion developed in the combustion chamber and the facility with which the piston conducts away the heat imparted to it. The rate at which the piston head transmits to the oil and the cylinder walls the heat which is imparted to it by the combustion chamber depends in turn on a, number of factors of the piston design including the number and extent of horizontal slots separating or partially separating the head from the skirt, the 'amount of metal in the ring flange and. in the connecters between the head and the skirt, the number and size of the piston rings, etc. In the example given above the radial clearance of the uppermost ring land at the ends of the major axis perpendicular to the wrist pin axis would be .001 of an inch per inch of piston diameter. Where the vertical width or extent of the ring lands is reduced by any of the arrangements shown in Figures 3, 4

tial minimum radial clearance varied from .002 l to .0035 of an inch per inch of piston diameter. The lower ring lands both in the present invention and in the prior art may, be given aprogr essively decreasing clearance, the amount of decrease also depending upon the conditions of operation of the piston in the engine. It will be understood, of course, that the present invention is not limited to all of the ring lands being provided with hearing faces as described.

Among the reasons for freedom from drag or scoring in a piston having such small clearances in the head portion is the reduction in contact area between the head and the cylinder wall. By reference to Figure 2 it will be observed that the bearing contact between the piston head and the cylinder wall is restricted to narrow vertical sections D and D' at the ends of the thrust face axis indicated at B. The head portion is thus free of cylinder wall bearing contact throughout the major portion of its periphery;-

When the piston heats up in operation both the skirt and the head increase in size and tend to reduce the clearance from the cylinder wall. The increase in size of the piston skirt in the type of piston having a yieldable skirt is absorbed by yielding'or flexing of the skirt. reduces the difference between the length of the major axis of the ring lands and the diameter through the centers of the thrust faces of the skirt until at full operating temperature these two diameters become substantially equal. That is to say, the skirt reaches full bearing engagement with the cylinder wall. Should the piston head be heated to apoint that it will tend to expand beyond this point the excess expansion is absorbed either by yielding of the ring flange as a whole so that the lower lands tend to be pressed to a more nearly circular form, or by actual deformation of the metal of the lands. Such deformation of the lands without binding or scoring in the cylinder is permitted because of the limited circumferential length of the portions of the lands which engage the cylinder wall. The lands at and near the top of the piston head cannot yield from their oval form whereas the lower portion of the ring flange may yield slightly. Accordingly, the lower ring lands may be pro- .vided with less clearance at the ends of their major axis than the upper lands or the length of the major axes of the ring flanges may increase or taper slightly from the uppermost to the lowermost land.

In some instances it may be desirable to further reduce the area of engagement of the ring lands with the cylinder wall by reducing the vertical height of the portions which engage. Three alternative ways in which this may be done are illustrated in Figures 3 to 5, inclusive In Figure 3 the lands 6a to 90. inclusive are each provided with a bevelled portion i3, which reduces the axial or vertical extent of the portion of the land which may bear against the cylin wall. In Figure 4 the lands 6b to 9b may :oved as at id to obtain a like reduction in the axiai extent oi the bearing surface. In Figure 5 the lands to; to 9d inclusive are illustrated as being -fstep-cut to leave annular ridges l5.

It is to be understood that the land structures illustrated in Figures 3 to 5 are to be employed in combination with an out-of-round head portion, for instance, such as illustrated in Figure 2 or 6. In such combination each of said land modifications will function somewhat differently and each is suited to a particular type or style of combustion engine or piston skirt construction. Since the modification of Figure 5 presents the least vertical extent of cylinder bearing con- This in a motor wherein the laterally acting forces,

such as indicated at 8 in Figure 1,required but slight resistive action in the lands of the head portion. The modification of Figure also has the advantage that the slight bearing contact surface will permit a rapid wearing-in of the land structure, and it also offers a factor of safety in the event of excessively high temperatures in the head portion.

The modification of Figure 4 is designed particularly to improve lubricating characteristics in the head portions, and the grooves it will, during the normal operation of the piston, contain a quantity of oil integral with the cylindrical film of oil about the piston, and will serve as a reservoir to maintain this film adjacent the head of the piston.

The modification illustrated in Figure 3 is designed to operate generally as in the embodiment of Figure l and the bevelled corners of the ring lands as at I3 will insure thatthe metal on the vertical face of the lands will not effect a peening action on the rings within the grooves. For instance, excessive expansion in the head portion due to high operating temperatures may cause aflow or Working of the metal vertically along'the land during piston reciprocation, and it is important that this Working of the metal be accommodated so as to prevent a binding of the piston ring within its groove.

- In the event that a piston is proportioned or designed so as to permit a tilting or movement in the direction .of the wrist pin axis the head portion may be contoured according to my invention as illustrated in exaggerated scale in Figure 6. In this form of piston ring land construction the head portion is shaped to provide a cross section wherein oval bearing portions; are presented on the wrist pin axis C as well as on the thrust face axis B. The piston head presents t a constantly increasing deviation from the circle defined by the cylinder to approach a maximum at points indicated at E intermediate the pin boss thrust face axes B and C. In this form ofJny invention I appreciate that-it may be necessary to reduce actual bearing contact 'area or provide a greater clearance between the head and the cylinder wall across the thrust face axis at B than in the preferred embodiment illustrated in Figure 2.

Although I have described certain embodiments of my invention in considerable detail, it will be understood that thoseskilled in the art may effect certain changes without departing from the scope of the invention and'that, therefore, I do not wish to be limited to the specific devices shown, but rather by the appended claims.

Iclaim:

1. A piston for internal combustion engines comprising a skirt having wrist pin bosses therein, and thrust faces on an axis normal to the wrist pin axis, a head 'having a depending ring flange integrally formed with said skirt, said ring flange having a non-circular cross sectional contour having bearing portions arranged immediately adjacent the wall of the cylinder in which the piston operates at the pin boss axis and at the thrust face axis, and portions intermediate each of said bearing portions having a greater clearance with respect to the walls of the cylinder than said bearing portions.

2. In an internal combustion engine, a cylinder having a circular cross-section, and a piston reciprocable in said cylinder provided with a skirt portion having opposed wrist pin bosses, an integrally formed head and ring flange provided with an oval cross sectional contour throughout its height, the major axis of said oval arranged normal to the pin boss axis, the diameter of the head and ring flange portion across said major axis being proportioned with respect to said skirt portion to bear against the wall of said cylinder to guide the piston during reciprocation.

3. A piston for internal combustion engines having a skirt portion provided with opposed thrust faces, pin bosses arranged on an axis normal to the axis across said thrust faces, an

integrally formed head and ring flange, said skirt being yieldable to permit the same to flex in response to laterally. acting forces during piston operation, said head and ring flange proportioned to-present an oval cross sectional contour" throughout the height of the ring flange with the majoraxis of said oval coincident with said thrust face axis, the diameter across the thrust face axis in the head and ring flange proportioned with respect to the diameter of the skirt to bear against the wall of. the cylinder within which the piston operates whereby to guide the same in a truly straight line reciprocation.

4. A piston for internal combustion engines comprising a skirt portion having opposed wrist pin bosses, a head and ring flange integral with said skirt above said pin bosses andseparated froin said skirt on each side of said pin bosses by a horizontally extending slot, said head and ring flange provided with a non-circular cross section throughout the height of the ring flange having its maximum diameter normal to the axis along said pin bosses and proportioned to bear against the cylinder wall above said horizontal slot whereby to guide the piston vertically during its reciprocation.

5; A piston for an internal combustion engine comprising a skirt portion having opposed wrist pin bosses, opposed thrust faces arranged upon an axis normal to the axis along said wrist pin bosses, a head and depending ring flange integral with said skirt above said wrist pin bosses and separat: ed from said skirt by a horizontal slot above said thrust faces, said head and ring flange shaped to provide an oval cross section throughout the height of the ring flange with the major axis arranged normal to said pin boss axis, the diameter in the head and ring flange on said major axis being proportioned with respect to the axis across the thrust faces in the skirt portion of the piston to permit said head and ring flange portion to bear against the wall ofthe cylinder in which the piston operates immediately adjacent said major axis to prevent tilting of the piston in the direction ofsaid major axis in response to forces acting laterally upon the piston during operation.

6. In an internal combustion engine, a cylinder having a circular cross-section, and a piston reciprocable in said cylinder including a skirt portion having opposed wrist pin bosses, an integrally formed head having a depending ring flange, said head and ring flange provided with an oval cross sectional contour, ring lands formed on said depending ring flange and each provided with an oval contour corresponding to the head and ring flange, said ring lands being cut away on their edges to provide a space intermediate the outer periphery of the ring land and the rings between said lands.

7. In an internal combustion engine, a cylinder having a circular cross-section, and a piston reciprocable in said cylinder including a skirt portion provided .with opposed wrist pin bosses, an integrally formed head having a depending ring flange, said head and ring flange provided with an oval cross sectional contour throughout the height of the ring flange, the major axis of said oval arranged normal to the axis along said pin bosses, ring lands formed on said depending ring flange, said ring lands being cut away on their edges to provide a space intermediate the outer periphery of the ring land and the rings between said lands.

8. In an internal combustion engine, a cylinder having a circular cross-section, and a piston "reciprocable in said cylinder including a skirt portion provided with opposed wrist pin bosses, an integrally formed head having a depending ring flange, said head and ring flange provided with an oval cross sectional contour throughout the height of the ring flange, the major axis of said oval arranged normal to the axis along said pin bosses, the diameter in the head and flange across said major axis proportioned with respect to the corresponding diameter in the skirt portion and with respect to the diameter of the cylinder to permit said head and ring flange to bear from the upper edge of the head above each of said thrust faces, each of said bearing'faces presenting circumferentially a constantly increasing deviation from said circular cylinder, the area of least clearance on said bearing faces being coincident with the axis of the thrust faces normal to the wrist pin axis.

10. In an internal combustion engine, a cylinder having a circular cross-section, and a piston reciprocable in said cylinder comprising a skirt head having a depending ring flange provided with curved bearing faces extending downwardly from the upper edge of the head above each of said thrust faces, atleast one of said'bearing faces presenting circumferentially a constantly increasing deviation from said circular cylinder, the area of least clearance on said one bearing face being coincident with the axis of the thrust face normal to the wrist pin axis.

11. Inan internal'combustion engine, a cylinder having a. circular cross-section, and a piston reciprocable in said cylinder comprising a head and skirt portion, said head portion comprising an integral casting solid throughout the perimeter and said skirt portion being flexible, said skirt portion provided with thrust faces on an axis'normal to the wrist pin boss axis, said head portion having a non-circular cross sectional contour extending downwardly from its upper edge with a maximum diameter coincident with the axis of said thrust faces, said maximum diin upon an axis normal to the axis of said wrist pin bosses, ahead and a depending ring flange secured to said skirt above said wrist pin bosses and separated from said skirt by a horizontal slot above'said thrust faces, the upper surface of said head and said ring flange shaped to provide an oval head section above one of said thrust faces, the major axis of said oval head section extending normal to said pin boss axis, the maximum diameter of said head and ring flange being across said major axis and the piston being proportioned to provide a maximum diameter across said thrust faces exceeding a maximum diameter of the head along said major axis thereof.

13. In an internal-combustion engine, a cylin- T.

cular.cross sectional contour providing spaced curved bearing surfaces and alternate spaced relieved areas having a greater clearance with reameter being less than the maximum diameter across said thrust face axis.

12. A piston for an internal combustion engine comprising a skirt portion having opposed wrist pin bosses, opposed thrust facesarranged therespect to said cylinder than said curved bearing surfaces, said bearing surfaces and relieved areas extending downwardly from the upper edge of the head, at least one of said curved bearing surfaces arranged on an axis normal to the wrist pin axis to prevent tilting of the piston within the cylinder about said wrist pin axis.

14. In an internal combustion engine, a cylinder having a circular cross-section, and a piston reciprocable in said cylinder comprising a head and skirt portion, said skirt having opposed wrist pin bosses therein, said head having a non-circular cross sectional contour providing spaced I curved bearing surfaces, each of said curved bearing surfaces presenting a constantly increasing deviation from said circular cylinder, and alternate spaced relieved areas having a greater clearance with respect to said cylinder than said curved bearing surfaces, said bearing surfaces and relieved areas extending downwardly from the upper edge of the head, at least one of said curved bearing surfaces arranged on an axis normal to the wrist pin axis to prevent tilting of the piston within the cylinder about said wrist pin axis.

15. In an internal combustion engine, a cylinder having a circular cross-section, and a piston reciprocable in said cylinder including a head and skirt portion, said skirt portion provided with opposed wrist pin bosses and thrust faces arranged on an axis normal to the axis of said wrist pin bosses, said thrust faces separated from the head of the piston by a horizontal slot above each of said faces and arranged to flex independently of said head in response-to lateral thrust, said head having a non-circular cross section with a maximum diameter coincident with the axis of said thrust facesand being relieved on each side of said axis, the diameter of said piston across said thrust faces exceeding the diameter of the head portion thereabove and flexing in response to lateral thrusts to bring said head into cylinder wall bearing contact and prevent tilting of the piston within the cylinder about the wrist pin 16. In an internal combustion engine, a cylinder circular in cross-section and a piston reciprocable therein comprising a head having a crown and 9. depending ring flange, and a skirt having aligned wrist pin bosses, said crown and ring flange being oval in cross section throughout their height, with the major axis of the oval perpendicular to the wrist pin axis.

17 In an internal combustion engine, a cylinder circular in cross-section and a piston reciprocable therein comprising a head, wrist pin bosses, and a skirt, said skirt having thrust faces on an axis normal to the wrist pin axis and bearing on said cylinder, saidhead having a depending flange grooved on the outside to receive packing rings and to provide circumferential lands on opposite sides of the grooves, at least one of said lands being in a plane above said wrist pin axis and having a non-circular sectional contour providing a bearing face above one of said thrust faces, the clearance between the cylinder wall and the bearing face of said last mentioned land being of such dimension as to permit the said bearing face to bear against the cylinder wall and serve as a guide to prevent-tilting of the piston and thereby restrict the piston to a truly vertical reciprocation within the cylinder and avoid audible slap.

18. In an internal combustion engine, a cylinder circular in cross section and a pistonreciprocable therein, comprising a head, wrist pin bosses, and a skirt, said skirt having thrust faces on an axis normal to the wrist pin axis and bearing on said cylinder, said head having 9. depending flange grooved on the outside to receive packing rings and to provide circumferential lands on opposite sides of the groove, at least one of said lands being in a plane above said

Images