US2400157A - Brazed cylinder muff - Google Patents

Description

May 14, .1946; A. A. MERRY 2,400,157

BRAZED CYLINDER MUFF Filed Sept. 11, 1943 2 Sheets-Sheet 1 INVENTOR flriiaazrflj ferry May 14, 1946; A. A. MERRY BRAZED CYLINDER MUFF Filed Sept. 11, 1943 2 Sheets-Sheet 2 l "mini": I

Patented May 14, 1946 UNITED STATES PATENT OFFICE BRAZEDmERMUFF Arthur A. Merry, West Hartford, Conn., to United Aircraft Corporation, East aasignor Hartford,

Conn., a corporation of Delaware Application September 11, 1943, Serial No. 501,982 2 Claims. (Cl. 257-261) This invention relates to improvements in heat transferring structure and has particular reference to an improved heat radiating structure for internal combustion engine cylinders and to an improved method of making the same.

An object of the invention is the provision of an improved unitary heat radiating structure and more particularly such a structure especially adapted for use on the cylinders of aircooled engines of the type used in aircraft.

A further object of the invention is the provision of a cylindrical finned mufi of the character indicated having improved heat abstracting and radiating characteristics.

A further object of the invention is the provision of a brazed or welded aluminum cylinder mull. made from sheet metal stampings.

A still further object of the invention is the provision of such a muii' in which the fins are shaped to form the cylinder cowling for directing a cooling stream of air through the fins.

A yet further object of the invention is an improved method of making aluminum mulls for air-cooled engine cylinders.

Other objects and advantages will be more particularly pointed out hereinafter or will become apparent from the following description.

I In the accompanying drawings,in which like reference characters refer to similar parts throughout, several forms of the invention are shown for purposes or illustration.

In the drawings- Fig. 1 is a fragmentary sectional view of a cylinder muiI embodying the invention;

Fig. 2 is a somewhat similar view on an enlarged scale showing a modified iln construction;

Fig. 3 is a sectional view taken on line 8-3 of Fig. 4 illustrating a further modified construction.

- Fig. 4 is a sectional view taken on line 4-4 of Fi 3;

Fig. 5 is a view similar to Fig. 3 showing a further modified construction; and i Fig. 6 is a sectional view showing the mull of Fig. 1 associated with an engine cylinder.

Referring to the drawings in detail and particularly to Fig. 6, the heat transferring structure is illustrated as a cylinder muii, generally indicated at III, mounted on the barrel portion II of an engine cylinder between a lower annular shoulder It and the cylinder head portion II. The particular cylinder shown is adapted to, be mounted on the crankcase 2| oi a conventional radial type engine used in aircraft, the usual external flange II and the stud and nut con- The muff I0 comprises a plurality of generally similar centrally apertured thin discs, or fins,

24 spaced apart by somewhat thicker rings, or spacers, 26 which are similarly apertured and extend around the apertures in the discs. These discs and spacing rings are secured together to form a unitary structure as by welding or brazing. The discs 24' which comprise the heat radiating fins of the mufi are made of soft aluminum which has good heat conducting qualities, while the spacers 28 are made of a harder, stronger aluminum alloy. When welded or brazed together the rings and the contiguous parts of the discs provide a strong sleeve portion for the muff adjacent the barrel portion I2 01" the engine cylinder which, when the muff is shrunk onto the cylinder barrel, provides intimate contact between the sleeve of the mud and the barrel of the cylinder as is required to obtain rapid and uniform heat flow from the cylinder to the mull. The importance of such a firm and uniform connection between the mufi and the cylinder will be evident when it is noted that the barrel I2 '01 the engine cylinder is very thin, as is customary in aircraft engine practice.

The discs 24 comprising the fins and the rings 26 comprising the spacers may be bonded together in any suitable manner, as by welding or brazing. A preferred method of brazing the stack of fins and spacers together consists in rolling out sheet aluminum from the billet with a coating of brazing material adhering to the surfaces of the sheet from which the fins and rings are stamped.

The fins and spacers are stamped out with the apertures therethrough slightly smaller than the outside diameter of the barrel. The mun is then assembled with the apertures in the fins and spacers in vertical alignment, preferably about a mandrel. Pressure is then applied longitudinally to the sleeve of the mufi' while the mui! is heated to brazing temperature, at which the brazing material on the surface of the fins and spacers fuses. Pressure is maintained on theassembledfinsandspacersuntilthemufihal cooled below the bracing temperature. The inside of the sleeve is then finished to accurate dimension to enable it to be heat shrunk onto the cylinder barrel II in a usual manner.

As a result, a unitary structure is provided in which the fins It which are of soft aluminum conduct the heat very readily from the cylinder side walls with which their inner surfaces are constantly maintained in direct pressure contact. while the spacers It, being of stronger aluminum alloy, provide the necessary strength to enable the mill! to be shrunk onto the cylinder barrel with sumcient pressure to maintain this good heat conducting relationship between the mull and the cylinder.

It will be further noted that as a result of this construction the fins can be spaced more closely together than has been possible with the solid forged type of muif previously used in which the fins were formed by machining grooves in the form. Moreover, the present construction by utilising soft aluminum material for the fins enablea faster heat conduction from the cylinder wall while permitting as good or even better heat conductivity as the result of the stronger pressure provided by the shrinkage strength of the aluminum alloy spacers between the fins. It will also be noted that considerable saving in material, lncuttingtoolcostsandinlabcrisefiectedby the above described method of uniting the stamped aluminum fins and spacers into an intesral muff.

In Fig. 2 the fins 24 are provided with indentations, or dimples, 2| located adjacent the outer periphery of the fins. Preferably these dimples are staggered so that the dimple in one plate is ofiset relative to the dimple in the next adjacent plate. As shown in Fig. 2 the dimples 2| are provided in alternate fins at diiferent distances from the vertical axis of the mufi to provide a radially staggered arrangement, although it will be obvious that all of the fins could be stamped with the same die and the staggering could be accomplished by assembling the fins in difi'erent angular relation to provide circumferential staggerlng of the dimples. The dimples have a slightly flattened bottom surface It and are of the same depth as the interfin spacing so that each fin vdll be engaged by the dimple of an adjacent fin. This is especially important where very thin Ind soft aluminum sheet is used for the fins. serving not only to prevent vibration of the fins but also to support the same adjacent their free outer periphery and prevent sagging.

The provision of the dimples It has a further advantage in that it increases the cooling area The cooling efiect of these dimples is considerable since they project into a part of the air stream which otherwise does not contact the fin area.

In Figs. 3 and 4 a modified fin construction is own in which the heat abstracting eifect of II is made even more efiective. in construction the fins a are made of very thin sheet stock and the spacers "a are also made thinner so as to provide very close spacing betweenthefins. Hereitwillbenotedthatthe spacers "a have their radial thickness increased so as to provide the same strong holding pressure flanges 80 which depend therefrom a sufiicient distance to engage the top surface of the next lower fin and provide a peripheral support for the latter while also closing the interfin space between adjacent fins. Portions of these fianges II are cut away at diametrically opposite sides of the cylinder to provide inlet and outlet areas "and It for the airstream passing across the engine cylinder, the portions of the flanges III which are not removed constituting in conjunction with the sleeve of the muff, semi-circular air passage means between the fins. In this modified construction dimples Ila and "b are provided in the fins in two annular rows arranged in staggered relation as indicated in Fig. 3. Also it will be noted that the dimples of adjacent fins are staggered so that the dimples provide vertical support for the thin fins as well as projecting into the semi-circular air streams passing between the fins in such manner as to cause the air to follow a tortuous path as it passes therebetween.

In Fig. 5 a still further variation of fin con struction is shown. In this form of the invention the fins are stamped out with opposed peripheral extensions it which are provided with a series of V-shaped notches it at spaced points along their periphery to'provide a series of cars 40. These ears are then bent at right angles to the plane of the fin to provide fin cowling similar to that described in'connection with Figs. 3 and 4, it being noted that in bending the ears til the notches II become closed and permit the ears to form the smooth peripheral flanges shown in full lines in Fig. 5.

As a result of these improvements it will be evident that a cylinder mail has been provided which is light in weight, utilizes a minimum of material and enables softer, better heat conducting thin material to be used than has hereto been possible with the forged type mull. It will also be evident that this improved construction enables greater heat transier and better distribution of the cooling .air stream due to the provision of dimples in the fins while also enabling the cylinder cowling to be formed integral with the fins and thus also to assist in dissipating the heat. It will also be evident that as a result of the builtup muif construction from sheet metal stampings any desired spacing of the fins is possible, all limitations as regards machining grooves being eliminated. Further, the improved brazed sheet metal construction and the method of forming the fins and spacers into an integral unit by brazing results in a considerable saving in labor and material.

While there are shown in the accompanying drawings several embodiments which the invention may assume in practice, it will be understood that these are shown for purposes of illustration only and that numerous changes may be made in the construction and arrangement of the parts without departing from the scope of the invention as defined in the following claims.

Having now described the invention so that others skilled in the art may clearly understand the same, what it is desired to secure by Letters Patent is as follows:

1. In an air-cooled cylinder for an internalcombustion engine, a cylinder barrel and a. heat dissipating muff shrunk thereon, said mufi' comprising a stack of alternately arranged fins and spacers having aligned apertures therein for receiving said cylinder barrel, the fins of said mufi being formed of soft aluminum having a high ooefilcient of thermal conductivity and the spacers being formed of harder aluminum alloy, said said cylinder barrel, the tins of said muff comprising preformed sheets of thin soft aluminum having a high coemcient of thermal conductivity and said spacers comprising preformed rings of thicker sheets of harder aluminum alloy, said fins and spacers being integrally united at their contacting surfaces with the apertures in alignment to iorm a sleeve having the inner peripheral edges of both said tins and spacers in pressure engagement with said barrel throughout the range of engine operating temperature.

ARTHUR A. MERRY.

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