US1969470A - Piston - Google Patents

Description

Aug. 7, 1934.

w. c. MCCOY PISTON Filed May '15, 1950 2 Sheets-Sheet 1 INVENTOR Millzlaan 6. BY

ZVM I ma ATTORNEYS) W. C. M COY Aug. 7, 1934.

PISTON 2 Sheets-Sheet 2 Filed May 15, 1950 VIINVENTOR Will C.MQ 6(3) BY I am p .2 70

ATTORNEY Patented Aug. 7, 1934 PATENT OFFICE PISTON William C. McCoy, Shaker Heights, Ohio, assignor to The Cleveland Trust Company, Cleveland, Ohio, a corporation of Ohio I Application May 15, 1930, Serial No. 452,601

- 6 Claims. 01. 309-14) This invention relates to pistons for use particularly in internal combustion engines.

High degree of heat conductivity of the piston head and relatively close "fit of the piston skirt or guide portion in the engine cylinder are essential features that tend toward the most efl'icient operation of modern high compression internal combustion engines. Furthermore, the long lived wearing characteristics of cast iron piston skirts and the low coefficient of heat expansion of iron alloys are important factors in obtaining close operating fit of the pistons in engine cylinders with a minimum frictional resistance. 7

Numerous attempts have been made to cast aluminum alloy piston head portions on cast iron and sheet metal piston skirts but, so far as applicant is aware, all of these proposed pistons are so constructed that thermal expansion of the piston head carries portions-of the piston skirt outwardly with it during operation of the piston, so that the major benefits of the composite piston construction are not obtained.

One of the objects of the present invention is to provide a piston in which the head may expand independently of and without materially affecting the skirt thereof.

Another object is to produce an inexpensive and efficient piston of such construction as to provide a close working fit of the piston in the cylinder and to embody the'advantages of high thermal conductivity of the piston head.

Another object is to produce a simple, light weight, durable and eflicient piston peculiarly adapted to meet the conditions which exist within an internal combustion engine cylinder including means for compensating for the stresses and strains imposed upon the piston, principally during the explosion stroke and for effectively dissipating the heat transmitted to the piston head 0 at that time.

A further object is to provide a composite piston having a head and skirt of dissimilar metals having relatively different coefficients of heat expansion wherein a close fit may be maintained between the piston and cylinder wall under all operating conditions, without causing piston slap and oil pumping when the-engine is operating cold, or seizing with and scoring of the cylinder when the engine is operating hot, and wherein the head and skirt are free to expand and contract independently of each other.

With the above and other objects in view which, will be readily recognized from the following detailed description, the invention consists in certain novel features of construction which will be readily understood by those skilled in the art to which this invention appertains.

Purely for the purposes of disclosure herein, I have selected to illustrate and describe one construction of skirted piston and two modifica- 6o tions thereof embodying my improved features.

In the drawings, Figure 1 is a fragmentary side elevation of my improved piston, looking toward the explosion thrust face thereof; one of the wrist pin bosses and portions of the head and skirt being shown in section.

Fig. 2 is an axial section of the piston shown in Fig. 1 taken through the working faces thereof.

Fig. 3 is a partial top plan view of the piston shown in Fig. 1, a portion of the same being shown in section; which section is taken approximately on'the line 3-3 of Fig. 1.

Fig. 4 is an axial section similar to Fig. 1, of a modified type of piston in which the wrist pin bosses are formed in the piston skirt. 7

Fig. 5 is a partial side elevation and sectional view of a further modified type of piston.

Fig. 6 is an axial section taken approximately on the line 66 of Fig. 5; and

Fig. 7 is a transverse section taken on the 7-7 of Fig. 5.

My invention contemplates the simplification of the construction and manufacture of pistons embodying a head .and skirt of two different metals, and of considerably lightening the same as compared with the conventional cast iron structures heretofore used while keeping the advantageous features and eliminating the disadvantageous features thereof. 1

Referring to the accompanying drawings, in which like numerals refer to like parts throughout the several views, the skirt or guide portion 1 of the piston is preferably made of cast iron or other suitable wear-resisting material having a relatively low coefficient ofheat expansion, and is formed with diametrically opposed apertures 2 through its walls concentric with the axis of the wrist pin bosses, to permit the insertion and withdrawal of the wrist pin which connects the piston bosses to the engine connecting rod.

The piston head is preferably of aluminum or other light weight alloy and comprises an end wall 3 and an annular side wall 4 which is formed with a suitable number of ring grooves 5 for the reception of the piston rings 6. The interior 105 of the side wall 4 of the piston shown in Figs.

1 and 2 is provided with spaced depending wrist pin bosses '1 which lie within the sldrt, and with suitable ribs 8 extending upwardly from the wrist pin bosses '7. to the head end wall 3.

line 0 The principal function of the head is to assist in translating the heat of the burning gases in the engine cylinder into mechanical energy, dissipate a part of the heat, and to carry the piston rings in such manner that they will coact properly with the inner walls of the engine cylinder. The head obviously expands when subject to the hot gases, and inorder to prevent this expansion from materially affecting the skirt to produce a similar expansion thereof adjacent the head, the head is secured to the skirt 1 only at one side of the wrist pin bosses 7, it being free to expand from the points of attachment toward the opposite side of the skirt relative to the skirt. During this expansion the head is substantially guided by the skirt.

In the manufacture of the piston shown in Figs. 1, 2 and 3, the cast iron skirt 1 is provided with an inwardly and radially extending circumferential flange 9 at its upper open end, the upper side of this flange being flush with the skirt walls and disposed in a plane perpendicular to the skirt axis. The lower face of the flange 9, however, is formed at a slight angle so that it tapers from the walls of the skirt toward the upper face thereof. The flange 9 is also provided with a number of slots or openings at one side thereof which preferably lie within an angle not greater than ninety degrees. This angle of extent may be greater, if desired, as it depends somewhat on the piston diameter and the desired relative expansibility of the head and skirt.

The piston skirt 1 just described is heated and placed in a suitable 'mold cavity and molten aluminum alloy or other suitable allow is poured into the mold cavity to form the piston head previously described. The metal as cast lies at opposite sides of the skirt flange 9 and at the one side of the skirt extends through the openings 10 to provide connecting portions 11 which integrally connect the metal lying on opposite sides of the flange at that side, as shown in Figs. 2 and 3.

As the molten metal forming the head sets and cools, it contracts and in so doing withdraws from the skirt 1 and its flange 9 toward the connecting portions 11 so that, in final condition, the head is eccentrically positioned with respect to the skirt 1 as shown in Fig. 3. This leaves a space 12 of varying depth between the head and skirt. Upon subsequent expansion of the piston head when in operation in an engine, the clearances thus provided permit the head to expand independently of the skirt without objectionably distorting it.

The degree of taper of the lower face of the piston skirt flange 9 may be readily calculated for any particular size of piston by taking into account the degree of contraction of the piston head relative to the piston skirt during cooling of the casting. The metal of the piston head contracts both radially and longitudinally of the piston body, so that it would tend to bind on the flange 9 of the piston skirt if this flange were not provided with suflicient angularity to permit 'the head to withdraw somewhat from the skirt.

The angularity of the skirt flange 9 is preferably confined to the under face of the flange in order to permit true diametric contraction of the piston head'without distortion caused by relative longitudinalmovement of the piston head and also to provide a top flange surface that is disposed at right angles to the axis of the piston body for receiving explosion thrusts in directalignment with the piston axis.

The openings in the piston skirt are also outwardly flared to insure that the boss portions of the piston body will shrink away from the skirt without binding in the boss openings. If binding occurs at this point it tends to weakenthe head casting and distort the skirt. The skirt is heated prior to casting it with the head in order to prevent premature chilling of the head metal during the casting on of the piston head.

'After the casting operation, the head is machined to the correct size with the side wall 4 at one side substantially flush with the piston skirt at the explosion thrust side of the piston, which is the side of the piston at which the head and skirt are connected by the connectors 11. The regions 22 of the skirt are then relieved as indicated in the drawings.

The modified construction shown in Fig. 4 comprises a head 13 and skirt 14 which are formed in the same manner as just described. This construction differs from that of Fig. 1 only in that the wrist pin bosses 15 are formed integral with the cast iron piston skirt 14.

The modified construction shown in Figs. 5 to '7 differs from the constructions of Figs. 1 and 4 in that the skirt 16 is formed with a partial flange .from the skirt, as previously described, flexing the spring member 19 as shown in Fig. 6. The flexible flat spring member 19 serves in the same way as the flange 9 of the piston shown in Fig. 2,

='to prevent relative axial movement of the skirt and head during the suction stroke of the piston.

Each of the pistons shown and described may be provided, if desired, with an area of relief 22 over the wrist pin bosses.

In operation, the several piston constructions embodying the present invention, shown and described, function in the same manner, and the skirts thereof may be fitted with a minimum of clearance with the cylinder walls since they are ,not materially affected by heat from the cyliner heads and further since the present invention makes it possible to employ a piston skirt material having substantially the same coeflicient of heat expansion as the cylinder walls.

By using a material for the piston skirt the same as the cylinder walls, the piston will operate when the engine is cold without any tendency to slap, which is the tendency of the present day aluminum skirts fitted in the cylinders with-a relatively large clearance.

The piston head as it becomes heated due to increased loads, long continuous operation, or

other well-known conditions, gradually expands outwardly from the points of attachment with the skirt, relative to the skirt, the space of varying dpth between the head and skirt permitting such expansion. In the case of the pistons shown in Figs. 2 and 4, the tapered face of the piston skirt.

flange 9 compensates for the axial expansion of the head and thereby prevents a loosening up of the abutting connection therebetween.

The present invention provides a piston construction of dissimilar metals having different coeflicients of heat expansion wherein a close flt may be maintained between the piston skirt and engine cylinder in order to obviate piston slap and oil pumping when the engine is operating cold and to prevent seizing with and scoring of the cylinder walls when the engine is operating hot.

In the pistons hereinbefore described, the portion thereof subjected to the greatest heat (the piston head) is free to expand independently of the portions subjected to the least heat (the piston skirt). The present invention thus provides relatively light weight pistons for internal combustion engines which can be economically manufactured, which embody the advantageous characteristics of the heretofore used iron and aluminum pistons, and which do not have the objectionable and disadvantageous features of either.

Furthermore, it is to be understood that the particular forms of piston shown and described, and the particular method of manufacture set forth, are presented for purposes of explanation and illustration and that various modifications of the piston construction and method of manufacturing it can be made without departing from the invention as defined in the appended claims.

What I claim is:

l. A piston comprising a skirt having an inwardly extending radial flange at one end thereof, a head of different metal cast about said flange, the metal of said head at opposite sides of said flange being integrally united through said flange at one side portion only of said skirt.

2. A piston comprising a skirt having an inwardly extending radial flange at one end provided with openings therein at one side of said piston, a head of a different metal cast about said flange, the metal of said head at opposite sides of said flange being integrally united through said openings, wherebysaid head may expand transversely to the axis of said piston independently of said skirt.

3. A piston comprising a cast iron skirt having an inwardly extending radial flange at one end thereof provided with openings therein at the explosion thrust side of said piston, an aluminum head cast about said flange, the metal thereof at opposite sides of said flange being integrally united through said openings, whereby the head may expand transversely to the axis of said piston independently of said skirt.

4. A piston comprising a cast iron skirt having an inwardly extending flange portion at one end thereof, said flange portion being arranged at a thrust face of said piston and having transverse openings therein, an aluminum head cast about said flange portion and within said skirt, the metal of said head at opposite sides of 'said flange portion being integrally united through said openings, and during the cooling thereof, being eccentrically drawn away from said skirt toward said integrally ,united portions to permit subsequent expansion of said head independently of said skirt.

5. A piston comprising a head and a skirt of dissimilar metals, and wrist pin bosses carried by one of said parts, said skirt-having a radially inwardly extending flange at one end thereof, said flange having apertures therein at the explosion thrust side only of said piston, the metal of said head being disposed continuously at both radial sides of said flange and also being disposed in said apertures at the one side of said skirt.

6. A piston comprising a head of one metal, a skirt of a difierent metal, said head and skirt being rigidly secured together at one side only of said piston, and a yieldable member secured to said head and to said skirt at the opposite side of said piston to permit relative transverse movement of said head and skirt at said last mentioned side during relative expansion and contraction of said head and skirt.

WILLIAM C. MCCOY.

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