US1909633A - Steel strut aluminum piston - Google Patents

Description

May 16, 1933.

R. E. RASMUSSEN STEEL STRUT ALUMINUM PISTON 'Filed Feb. '7,- 19:51

Patented May 16, 1933 UNITED STATES I l p 1,909,633

RIGHABD E. RASMUSSEN, F DETROIT, MICHIGAN STEEL STRUT ALUMINUM PISTON -Applioation led February 7, 1981. Serial No. 514,193.

My invention relates to cast metal pistons for internal combustion engines of the type wherein two struts extending transverse to the axis of the piston pin are placed inthe mould and embedded in the metal of the' chosen so as to cause the diameter to increase at substantially the same rate as the diameter ofthe cylinder in which the piston operates increases as the engine becomes heated.

Such pistons are commonly made of aluminum or of an alloy of which aluminum forms the principal ingredient, and inasmuch as aluminum expands faster than castV iron, the material from which the cylinder of the engine is made, the piston if it fits properly when the engine iscold will tend to `score the cylinder wall and seize therein as the parts become heated; and on the other hand if such a piston is made small enough in diameter so as not to bind when the engine is hot it will be so loose in the cylinder as to be noisy, the phenomena of piston slap, when the engine is being started from a cold condition. The scoring or seizing being a fault particu 30 larly to be avoided the result is that aluminum pistons are commonly made smaller in diameter even than is necessary for proper running at high temperatures,

with the result that such pistons are ordinarily more noisy than cast iron pistons.

As herein first appears, such pistons have heretofore been provided with transverse struts which expand not at all, or at a rate much less'than that of aluminum, in order 40 to maintain, as nearlyv as possible, a constant diameter of piston as the engine becomes heated; or a diameter which increases at approximately the same rate that the diameterY lof the cast iron cylinder of the engine increases. In such pistons, however, no provision has commonly been made for controlling the diameter of the bearings for the piston pin and, inasmuch as it is highly desirable that the bearing surface for the pin shall be of the same aluminum or equivalent metal as that from which the piston is cast, the fit ofthe steel piston pin in the aluminum bearings therefor has Varied with the temperature; being tighter when the engine is cold and looser, because of the more rapid expansion of the aluminum bearings than the expansion of the steel pin, when the parts have become heated; the result'being that such looseness as is necessary to permit the assembling of the parts and operation without binding orscoring at low temperatures, will increase to an objectionable degree as the engine becomes hot.

The object of my invention therefore is to provide a piston wherein and in addition to the controlling of the external diameter thereof the diameter of the bearings for the piston pin will also be controlled, thus providing a piston wherein the clearance between the pin and its bearings as well as the clearance between the piston and the cylinder will be constant or substantially so at all temperatures. The preferred form of my invention is illustrated in the drawing `accompanying and forming a part of this specification; although the same may be embodied in other forms, and my invention includes such other A forms as come within the scope of the claims at the end of this description.

In the drawing: x

Figure 1 is a view showing a piston made in accordance with my invention, in elevatlon.

Figure 2 is a view partly in section upon a central vertical plane extending along the 85 axis of the piston pin bearings, as indicated by the line 2 2, Figure 1, and partly in elevation as seen from a position to the right of Figure 1.

Figure 3 is a view showing a section upon ,90

a plane at right angles to the axis of the piston and located at the axis of the piston pin bearings.

Figure 4y is a view showing the strut member of my improved piston in perspective, with its part separated.

Figure 5 is a view similar to Figure 1 but showing certain piston features not shown in Figures 1 to 3.

Figure 6 1s a vlew showing a section upon 10 l an inclined plane indicated-by the line 6-6,

liti:

Figure 5.

Referring now to the drawing and to the particular embodiment of my invention which it illustrates, the reference numeral 10 designates the head portion of the piston; and below the head and extending downwardly therefrom to form a guide or skirt portion are oppositely arranged slippers 11 which are ordinarily separated from the head by slots l2, so as to permit the head to expand without carrying the upper end of the skirt along with it. The lower ends of the slippers are ordinarily connected by arcuate connecting parts 13 to provide a complete ring at the lower end of the skirt or guiding part of the piston; although my invention, so far as it concerns the controlling of the expansion for the bearings for the piston pin, is equally useful in pistons not having the slots 12, and in which the slippers extend so as to form a complete cylindrical skirt portion for guiding the piston within the cylinder in which it operates.

Arranged below the head are piston pin bosses 14 for the two ends of a piston pin, not shown. rllhese bosses are shown as supported from the head by depending supports or piers 15. ln the form of my invention illustrated in Figures l'to 3 there is no connection formed by the cast-metal of the piston between the pin bosses and the skirt portion made up of the slippers 11 and lower connections 13, while in the form illustrated in Figures 5 and 6 there are connections 16 of cast metal between the pin bosses and the slippers which connect the head and bosses y, vand the skirt together and form an integral structure as the piston is cast.

rllhe parts thus far described are made from cast metal, commonly aluminum or aluminum alloy as explained, by the use of a suitable mould. As a matter of course the' periphery of the casting thus produced is .properly finished to provide a cylindrical tend from above the pin bosses downward and below the pin bosses.v These struts are placed in the mould and when the moulten metal is poured thereinto their central parts become embedded in the pin bosses, and their extremities in the slippers, in substantially the way shown in Figures 2 and 3.

Lacasse rlllhe metal of the struts must obviously be one which will not be melted by the fluid metal which forms the piston as it enters the mould and flows into contact with them. Steel is a good material for the struts, and

a steel may be chosen having a composition such that it expands very little with change in temperature; so that as the piston becomes heated in use its diameter will increase but slightly and at a rate not greater than the rate of expansion of the cast iron cylinder in which the piston operates. llnvar is also a suitable materia-l, although more expensive, and when an invar strut` is used a substantially constant diameter of piston at all temperatures is maintained because invar expands to but a negligible extent when it is heated.v rIhe struts therefore control the diameter of -the skirt as it can increase in diameter only to the extent that the struts expand and increase in length. This is so in the Figure 5 form no less than in the Figure 1 form because in the former the ties 16 in contracting place the struts under compression which is not relieved when the piston becomes hot in use, as it never attains a temperature even remotely approaching that of the piston metal when itl solidiies and commences to compress the struts and to set up contractile stresses in the ties 16.

Associated with the struts 17 and embedded in the piston pin bosses 14 are rings the purpose of which is to control the diameter of the bearings in the bosses for the ends of the piston pin. These rings may be variously provided, and variously arranged except that they must be larger in internal diameter than the diameter of the piston pin bearings, so that the bearing surfaces for the pin are always of the same metal as that from which the piston is cast. The rings are preferably integral with or fastened to the struts in order to provide a plan for conveniently and effectively supporting them inside the mould in such positions that they will be embedded in the bosses, as explained, although insofar as their function of controlling the diameter of the piston pin bearings is concerned theyneed not be fastened to the struts.

lln the form of my invention illustrated each struct has two rings,"although the two forme-in eect but a single ring. That is each strut has a Hange or ring 18 formed by Hanging the material of the strut, as shown, and which Harige extends substantially parallel with the piston pin bearing; and is provided with holes 19 through which the fluid metal runs during the casting of the pis ton. lln addition each strut is preferably provided with a second ring 20 having a base 21 fastened to the strut asby welding, and which second ring i-sV provided with holes 22 like and for the same purpose as the holes 19. The two rings are larger `)than the piston pin bearing to an extent suiiicient to provide a bearing surface inside the rings of the same metal as the metal from which the piston is cast, as appears in Figures 2 and 3.

The metal of the rings is of the same character as that of the struts, from which it follows that the diameter of the bearings for the two ends of the piston pin is controlled by the rings; and said rings, in addition to controlling the diameter of said bearings, provides a more secure anchoring of the struts in the piston pin bosses, as will be appreciated.

Having'thus described and explained my invention I claim and desire to secure by Letters Patent:

1. In a cast metal piston of the class described, a rectangular strut embedded in the piston during the casting thereof and extending transverse to the axis of a piston pin bearing between parts of the piston which are spaced apart from one another, and which strut has a ring upon each side thereof, which rings extend substantially parallel with said bearing and the diameters of which are materially greater than the diameter of said bearing; so that metal from which the piston is made will embed said rings during the casting of the piston and form a bearing of said metal inside the rings for the piston pin and whereby expansion of the bearing as the piston becomes heated will be controlled by said rings; said rings together being of a length corresponding, approximately, with the length of the bearing in which they are embedded.

2. In a cast metal piston of the class described, a rectangular strut embedded in the piston during the casting thereof and extending transverse to the axis of a piston pin bearing between parts of the piston which are spaced apart from one another, and which strut has two oppositely disposed rings one formed integrally therewith and the other formed separately and secured thereto, and which rings are substantially parallel with the axis of saidbearing and materially larger than said bearing, and have holes in their walls; so that metal from which the piston is formed will embed said ring during the cast ing of the piston and form a bearing for the piston pin of said metal inside the ring, and whereby expansion of the bearing as the piston becomes heated will be controlled by said rings; said rings together being of a length corresponding, approximately, with the length of the bearing in which they are embedded.

In testimony whereof I aix my signature.

RICHARD E. RASMUSSEN.

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