US2159989A - Welded two-piece light alloy piston - Google Patents

Description

May 30, 1939. v R. M. HAZEN ET AL 2,159,939

WELDED TWO-PIECE LIGHT ALLOY PISTON Filed April 19, 1937 s Sheets-Sheet 1 wwwa 1939- R. M. HAZEN ET AL 2.159,989

I I WELDED TWO-PIECE LIGHT ALLOY PISTON Filed April 19, 19.37 3 Sheets-Sheet 2 ELD 27 HIIIIIII WELD 4.

. 21 fiolla/a'fizgfazeiz & 773071145 5. WZaeft Patented May 30, 1939 2,159,989 WELDED TWO-PIECE LIGHT ALLOY PISTON Ronald M. Hazen and Thomas S. McCrae, Jr.,

Indianapolis, Ind., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application April 19, 1937, Serial No. 137,656

5 Claims.

This invention relates to pistons and especially to light alloy pistons for high speed engines.

It relates particularly to such pistons for use in internal combustion engines.

In modern high speed two-cycle engines, the conditions under which the pistons have to operate are particularly severe. Other things being equal, the specific output of a two-cycle engine tant to provide pistons which are light, but of adequate strength, while capable-of dissipating effectively the heat to which they are subjected.

The object of the invention is a strong, light Weight piston, capable of quickly dissipating the heat to which it is subjected.

Another object of the invention is a piston in which the heat fiow to the ring belt is limited.

Another object of the invention is a piston which can be oil cooled.

It is-a further object of the invention to achieve the foregoing objects in a piston which can be simply and cheaply produced.

The above and other objects of the invention will be apparent as the description proceeds.

According to the invention, the crown of the piston is supported from the piston pin bosses mainly by a circular strut forming an inner wall, spaced from and of greater section than the outer wall of thepiston and-providing an annular insulating air space between the two walls. The piston is made in two pieces subsequently fastened together by screwedand/or welded joints, or the like. One piece forms one part of the wall of the annular insulating air space and includes the crown and the other piece forms the remaining part of the wall of the annular insulating air space and includes the skirt.

The two piece construction permits of greater control and freedom in the choice of section and in the provision of suitable cooling fins and insulating air spaces.

The drawings show several modifications of a piston according to the invention.

r" In the drawings:

I is a view, partly in elevation and partly in section, of a preferred piston structure according to the invention.

Fig 2 is a view in elevation of a part of Fig. 1..

Figs. 3 to 8 are views, partly in elevation and partly in section, of modifications according to the invention.

Referring now to Figs. 1 and 2.

I is the piston crown and 2 is the piston skirt provided with diametrically opposite bosses such as 3, having bearings 4 for a piston pin (not shown).

Between the underside of each boss 3 and the piston skirt is a strengthening rib 5, and the uppermost surface of each of the bosses is a fiat shoulder 6 forming a seating for the circular strut I of the crown I of the piston.

Immediately above the shoulders 6, the bore of the piston skirt is screw threaded at I to engage with threads 8 at the lower end of the circular strut I.

The piston crown I is somewhat mushroom shaped and in the example illustrated has a spherical top with a rim 9 which fits closely within the bore at the top end I of the piston skirt but with part of the rim 9 extending therefrom when the crown with its strut is screwed on to the seatings 6.

The outer diameter of the circular strut of the piston crown between the rim and the threads 8, and the bore of the piston skirt between the top I0 and the threads I, are such as to leave an annular space I I between the strut and the skirt when these two parts are assembled.

The annular space extends closer to the outer cylindrical surface of the piston at points above and below a ring belt area I2 in which grooves I3 are provided for conventional packing rings (not shown).

Grooves I 4 with drain holes I5 therefrom to the inside of the piston are provided at the lower end of the skirt, for scraper'rings (not shown).

Cooling fins I6 are provided within the bore of the skirt 2, at a point in the annular air space I I above the ring belt area I2.

The inside of the crown I is provided with cir-- cumferential fins II giving ample cooling area therein.

The two parts-the piston crown and the piston skirtcan be made of any suitable light alloy (either forged or cast), and it will be seen that a structure has been provided in which all critical points as well as the cooling fins may be completely machined to any desired tolerance limits ebefore assembly.

manner, after which the joint between the rim, 9

, of the piston crown and the; top end "lot the piston skirt is sealed by welding as indicated in the drawings.

Provision is made for efiective oil cooling of the piston by fitting a sheet metal oil retainer H8 in the piston, as shown. It is held in position by screws I9 in each rib 5 of the piston skirt.

The oil retainer is open at its upper end but forms an annular oil well 20 which traps a part of the cooling oil which may be projected in known manner from the engine lubricating oil pump up the connecting rod and against the underside of the piston crown.

Oil from the well 20 is thrown up against the underside of the piston crown and over the cooling fins l1 therein, as the piston decelerates in approaching its top dead center. Some of the oil projected or thrown against the crown is forced through radial holes 2| therein into the annular space H and on to the cooling fins l6 oi. the skirt 2 just above the ring belt area l2.

From the annular space H the oil returns through radial holes 22 back into the oil well 20.

The construction according to Fig. 3 is essentially similar to the construction according to Figs. 1 and 2, except that the ring belt area 23 is formed as a part of the piston crown 24, and the joint between the crown 2d and the piston skirt 25 to be sealed by welding is below the ring belt area 23, as indicated in the drawings.

The construction according to Fig. 4 is essentially similar to the construction according to Fig. 3, except that the strut, (i. e., the internal wall 26 of the annular air space 21 and the means for transmitting the loads on the crown of the piston to the piston pin) is formed as part of the piston skirt 28, the screw threaded connection between the piston crown 29 and the piston skirt 28 being towards the uppermost end of the piston, with the piston skirt 28 male threaded and the piston crown female threaded.

The construction according to Fig. 5 is essentially similar to the construction according to Fig. 4, except that the ring belt area 30 is formed as a part of the piston skirt 3|, and the joint between the piston crown 32 and the piston skirt 3! to be sealed by welding, is above the ring belt area 30, as indicated in the drawings.

The construction according to Fig. 6 is essentially similar to the construction according to Fig. 4, except that the piston skirt is female threaded and the piston crown is male threaded.

The construction according to Fig. '7 is essentially similar to the construction according to Fig. 5 except that the piston. skirt is female threaded and the piston crown is male threaded.

In "the modification according to Fig. 8, the piston pin bosses 33 are integral with the piston crown 35. The ring belt area 35 is also integral with the piston crown 34. The piston skirt 36 is a push fit over the bosses 33 and is welded to the piston crown 34 below the ring belt area 35, as shown.

While special provision for oil cooling has only been shown in conjunction with the preferred form of the invention shown in Figs. '1 and 2 by providing this with an oil retainer I8, and radial holes 2| and 22 through'the inner wall of the insulating annular space, it will be appreciated that such means might equally well be applied to the construction according to Figs. 3 to 8,

In all the examples illustrated, the heat-flow from the head of the piston to the ring belt area is restricted by the narrow section of metal between these two parts. The circular strut forming the inner wall of the insulating annular air space is sufiiciently large to carry the main gas pressure loads and the heat flow directly on to the piston pin bosses--only a small part of the load and the heat flow being transmitted through the outer section of the piston.

Because of the lower temperature of the ring belt area, due to the lessened heat flow to this part, the possibility of piston rings sticking, consequent on carbonization of the lubricating oil at the temperature which would otherwise exist, is avoided.

Complete machining of ample fin area of minimum section is permitted by the two piece construction.

Internal oil cooling is desirable in order efiectively to dissipate the greater heat flow to the inside of the piston, where the heat flow through the ring belt area and the piston rings tothe cylinder wall has been reduced to a safe limit in the manner set forth.

We claim:

1. In a piston having a crown, a skirt, piston pin bosses, and a ring belt area in the outer wall of the piston between the crown and the piston pin bosses, a strut to support the crown from the piston pin bosses and forming an inner wall spaced from the outer wall of the piston to provide an enclosed annular insulating air space between the ring belt area and the strut forming the inner wall, said inner. wall having at all points a greater cross-sectional area than points above and below the ring belt area in the outer wall of the piston, whereby only small portions of the gas pressure loads and the heat to which the crown is exposed in an engine cylinder are transmitted to the ring belt area, and the main portions of the gas pressure loads and the heat flow are carried directly through the inner wall to the piston pin bosses, said piston being made in two pieces subsequently fastened together, and having a joint in the outer periphery of the piston above the piston pin bosses, one of said pieces forming a part of the wall of the annular insulating air space and including the crown, and the other piece forming the remaining part of the wall of the annular insuiating space and including the skirt.

2. The combination according to claim 1, in which the ring belt area is part of the piece including the skirt and the strut is part of the piece including the crown.

3. The combination according to claim 1, in which the ring belt area and the strut are part of the piece including the crown.

4. The combination according to claim 1, in which, the ring belt area is part of the piece including the crown, and the strut is part of the piece including the skirt.

5. The combination according to claim 1, in which the joint in the outer periphery of the piston above the piston pin bosses is a welded joint, and there is an additional screw threaded connection between the two pieces.

RONALD M. HAZEN. THOMAS s. MCCRAE, JR.

. v CERTIFICATE OF CORRECTION. Patent No. '2, 159,989. M y 3 959- i RONALDM.HAZEN,ETAL. -It is hereby certified that'error appeare in the printed specification of the above numbered patent requiring correction ae follows: Page 2', second column, line 51, claiml, before the word space'! insert air; and that the said Letters Patent should be read with this correction therein that the same may conform to the record .of the case in the Patent Office.

'Signed and sealed this'lst day of August, 1959. I

. H Henry van Aredale,

(Seal) 7 Acting Commissioner of Patents--

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