US2136416A - Piston - Google Patents

Description

Patented Nov. 15, 1938 UNITED STATES PATENT OFFICE PISTON poration of Illinois Application March 17, 1937, Serial No. 131,295

3 Claims.

' in two cycle engines, or engines having a relatively large cylinder diameter, or any type wherein the amount of power generated is great as com- 16 pared to the surface area of the cylinder available for the transfer of heat from the piston. An overheated piston tends to cause improperly timed firing of the fuel charge. Furthermore, where pistons formed of aluminum alloy or other metals 20 having relatively high coefllcients of expansion are employed, adequate heat dissipation from the piston, or temperature control thereof is necessary in order to mainatin proper operating clearance between adjacent surfaces of the piston and 25 cylinder.

As conventionally constructed, the head. end of the piston, or that part in the vicinity of the pis- ,ton rings, does not make rubbing contact with the cylinder walls and therefore heat must travel from 30 the high temperature piston head to the relative cooler cylinder walls through-the piston rings and through the skirt end of the piston.

An object of the present invention resides in the provision of a piston for an internal com- 35 bustlon engine, embodying improved means for augmenting the flow of heat therefrom, and especially from the head end of the piston. In addition to the aforesaid function of the means which constitute in part the subjectmatter of the 40 present invention, such means also serve automatically to size the head end of the piston to the particular cylinder which receives the same, in fulfillment of another object of the invention.

In the following description setting forth a pre- 46 ferred piston construction whereby the foregoingobjects are attained, the lands adjacent the grooves for the pistonor packing-rings are provided with narrow circumferential ribswhich project outwardly a small distance beyond the side 50 surface of the piston. These narrow ribs contact the inner wall surface of the cylinder, tending to flow or wear when the engine is operated for the first time. The ribs are quickly sized by coaction with the cylinder wall, or reduced to 56 the most desirable operating diameter, and being in direct contact with the cylinder wall provide a short path through which an appreciable amount of heat from the piston head is dissipated.

Stated generally, the object of the invention is to provide a piston embodying improved means for dissipating heat, and constructional features which result in an operating fit between the cylinder and piston closely approaching the ideal.

Other objectsand advantages will appear from the following detailed description and accomlll panyingdrawing which shows a piston constructed in accordance with the present invention.

Fig. 1 is a sectional elevational view showing a fragmentary portion of a cylinder with the piston, devoid of packing rings, therein; Fig. 2 is a top plan view of the assembly shown in Fig. 1; Fig. 3 is a bottom plan view of the piston, and Fig. 4 is a transverse sectional view of the piston, the section being taken at line 44 of Fig. 1.

My improved piston, preferably initially formed as an integral casting of aluminum alloy, is characteriaed by a head structure which includes a top plate 5 and a tubular side-wall portion 6, depending from the margins of the top plate a sufficient distance to accommodate a plurality of piston rings (not shown). The wall portion 6 merges into a tubular extension or continuation thereof, preferably of reduced wall thickness, which constitutes the piston skirt I.

Projecting from diametrically opposite sides, internally of the piston, are bosses 8 which are provided with alined bores therethrough to accommodate the ends of a wrist pin (not shown). Ribs 9 extending between bosses 8 and top plate 5, aid in transmitting the thrust forces imparted to the piston head to the wrist pin and otherwise serve to reinforce the piston structure. One of the bosses 8 is provided with a transverse bore In which, when suitably threaded, is adapted to receive a set screw or the equivalent for preventing axial displacement of the wrist pin. Formed on the inner side-wall surface of the piston are a series of fins II which extend longitudinally of the piston and project radially inwardly from its side wall. The fins Ii aid materially. in conducting and radiating heat away from the relatively high temperature piston head, the heat being transferred through the skirt 1 to the cylinder walls and, particularly in the case of a two-cycle engine, to the incoming fuel vapor and lubricatin: oil in the engine crankcase.

To allow for lateral expansion of the side walls under operating conditions, resulting in large measure from expansion of the pin bosses I, the

outer surface of the skirt 1 is machined to provide appreciable relief at areas in the vicinity way betweenthe pin bosses, the lands l3 extendof the pin bosses, the relieved areas, indicated at l2, Fig. 4,- extending the full length of the piston skirt. This machining process, termed nated l3, located on the outer skirt surface miding longitudinally of the piston from the lower extremity thereof approximately to the locality where the skirt merges into the piston head. The diameter of the piston between the. land surfaces is such that small tolerance or clearance is allowed between the -coacting lands and cylinder walls, thus providing for closely fitting surfaces at those areas of the cylinder wall where lateralcomponents ofpiston thrust are directed. The

lands l3 further provide paths of substantial surfacev extent for conducting heat from the pis-' ton to the cylinder wall.

As in the case of pistonsof conventional con- Y struction, the diameter of the headend of the piston is slightly reduced, thereby providing for an appreciable clearance between the piston head and cylinder and avoiding rubbing contact between these parts in the vicinity of the packing rings. 'R'ubbing contact is, of course, present between the packing rings and cylinder, and in conventional piston assemblies, the packing rings provide the only direct'path for the flow of heat from the piston to the cylinder wall.

For the purpose of augmenting heat flow from Q the piston head and improving the operating fit between the piston head and cylinder,'in.carry ing out a stated object of the present invention, the lands l4 between and adjacent the ring grooves l5 v are provided with narrow bandsor ribs is which are preferably formed'integrally with, and project laterally outwardly from the surface of the said lands. The initial diametral-dimension of the ribs 16, prior to any change thereof resulting from wear, is such as to provide'f'or a snug fit with the cylinder bore. In the early stages of engine, operation the ribs l6 wear, flow, or otherwise quickly reduce themselves to an ideal working diameter. Tests have proven that these nar-- row ribs do not cause scoring of the cylinder surfaces or in any way produce harmful effects.

and accordingly is provided with a deflector, or

baiiie H for preventing the fuel vapors from passing from the inlet port, directly across the cylinder bore to the outlet port. As heretofore designed and constructed the opposite ends of deflector I! are spaced an appreciable distance from the cylinder wall, and under no circuming engine operationstances is contact effected between the deflector ends and the cylinder. Being disposed within the firing zone, the deflector isv subjected to exceedingly high temperatures and it is desirable cam grinding", results in a pair of lands, desigf to provide a direct path for heat flow, to the end of dissipatingheat therefrom. Accordingly, in my improved piston, the deflector is tapered at its opposite .ends and terminates inrelatively narrow prolongations I8 which are adapted to contact the cylinder wall. The prolongations l 8 are sized to the cylinder in the same manner as are the ribs l6, previously described.

The substance of my invention is set forth inthe following claims, but it is understood that various changes or modifications within the purview of my invention may be made in the construction illustrated in the accompanying drawing and description above.

I claim:

1. A piston for use in the cylinder of an internal combustion engine, having head and skirt portions, an integral baiile member extending across said head portion, said baille member having relatively thin prolongations of ductile metal adapted to contact the wall of the cylinder dur- 2. A piston for use in a cylinder of a two-cycle internal combustion engine, having head and skirt portions, the head portion of said piston having circumferential grooves for receiving packing rings, and an integral bailie member extending across the top thereof, thin circumferential ribs of ductile metal projecting laterally from the piston adjacent said ring grooves, and thin prolongations of ductile metal at opposite ends of said bafile member, said ribs and prolongations being adapted to contact the cylinder walls during engine operation.

3. 'An aluminum alloy piston for use in the cylinder of a two-cycle internal combustion engine} said piston comprising integral head and skirt portions of diameter appreciably less than the bore diameter of the cylinder with which the piston is to be used, abaiile member formed on 'the top surface of said head portion, the opposite ends of said baflle member being relatively narrow and adapted to contact the cylinder wall,

' grooves for packing rings formed in said head portion, circumferential ribs projecting laterally outwardly, adjacent said ring grooves, said ribs being adapted to contact the cylinder walls, pin bosses projecting inwardly from diametrically opposite side surfaces of the piston. lands extending longitudinally of the outer skirt surface, spaced between said pin bosses, said lands being adapted to contact the cylinder walls, and aseries of radial, inwardly projecting fins extending along the inner side surfaces of'said head and skirt portions.

, WILLIAM C. DEHN.

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