US2293412A - Air-cooled cylinder head - Google Patents

Description

l Aug. 18, i942- E. c. sTElNER ETAL 2,293,412

AIR-GOOLED CYLINDER HEAD Filed Feb. 14, 1941 3 Sheets-Sheet l I l I f5 l f 52 r l 28 NVENTOR IDM/HRD aSTL'IMKw BY Elma. [LL

Aug. 18, 1942.

E. C. STEINER EVAL lAIR-COLED CYLINDER HEAD Filed Feb. 14, 1941- s sheets-Sheet 2l ATTORNEY Aug .18, 1942- E. c. STEINER ETAL 2,293,412

AIR-COOLED' CYLINDER HEAD Filed VFeb. 14, 1941 3 Sheets-Sheet 5 f g a wie oa.

M i I 6.. 2 "m l L f/ "K uw l ' m/ Y nl W 'IIN 7 1a Ill||||| f6 ,24' 19 24' INVENTORS EDMZRD CWI/maw BY EENPYCHILL ATTORNEY vPatented Aug. 128, 1942 2,293,412 Am-cooLEn CYLINDER HEAD Edward C. Steiner, Paterson, and Henry C. Hill,

Montclair, N. J., assignors to Wright Aeronautical Corporation, a corporation of New York y `Application February 14, 1941, Serial No. 378,890

1 Claim.

This invention relates to cylinder heads for air-cooled internal combustion engines and is particularly concerned with a type of cylinder head construction in which the cooling ns thereon are formed by machining operations rather than by the more common process of casting.

In the development of air-cooled aircraft enfgines, power has steadily increased and even with cylinders of relatively the same bore, the horsepower per cylinder has been greatly increased by increasing the area of cooling fins on both-the cylinder and head, permitting of engine operation at high mean effective pressure. With the increase in cooling lin area however, and with the greater power, the stresses in the cylinder and head become greater requiring an improvement 'in strength characteristics of the assembly. Conventional practice in recent years has consisted in the casting, from suitable aluminum alloys, of nn'ed cylinder heads, and casting and pattern practice has been materially improved to gain both greater cooling n area and greater strength. The limitsbf this practice are rapidly being approached and the present invention teaches va dillerent mode of cylinder head construction in which either castings or forgings of stronger material are used and in which a great number of deep coolingfins may be machined thereon, the number and depth of the ns probably being greater than those capable of being produced by any casting methods. In connection with this problem, it is preferable to make the cylinder head a unitary structure, in corporating therein valve seat openings, valve ports, and rocker box housings, some of which form protuberances on thecylinder head which ordinarilycause great `diiliculty if the complete machining of a cylinder headbe attempted. This ldiiiculty is attended, of course, by greatly increased cost of production.

An object of this invention is to provide a method of machining deep cooling iins on a metal body. A further object is to provide a novel method of milling. Still another object is to provide an improved form of cylinder head adapted for fabrication from strong alloys and adapted for the machining of cooling ns thereon in such a manner as to produce a strong, yet light aggregate structure. Still another object is to provide a particular form of finned cylinder head having improved strength characteristics and being adapted for attachment to a cylinder barrel'without the possibility, as encountered in previous practice, of cracking the conventional bursting stresses set up when the cylinder head is attached to the cylinder barrel.

Further objects, and an amplication of those above indicated, will be appreciated in reading the annexed detailed description in connection with the drawings, in which:

Fig. 1 is a plan of a cylinder head according to the invention;

Fig. 2 is a side elevation of the head including, in dot-dash lines, a representation of the milling cated'in the aggregate at III is initially formed as` a solid metal blank, either as a forging or casting of suitable alloys such as aluminum or bronze. The head is provided with integral rocker boxes I2 and I3 for intake and exhaust valves respectively, the boxes having valve guides I4 extending into valve ports I5 which register with valve seatl openings IB, the two valve seats being disposed at an angle to one another yat opposite sides of the cylinder head the internal shape of which is substantially hemispherical as shown at I 8 in Fig. 5. The lower part of the interior of the head is threaded as at I9 for attachment to a vcylinder barrel in the conventional manner.

-The head is likewise provided with openings 2|v for sparkplugs and' it will be apparent that the various' openings and parts thus far described may be readily formed by conventional machining processes. The head as shown is provided with a first plurality of vertical cooling fins 23 which extend from the bottom of the head a's at ,-24 in Fig. 6 upwardly and across the top of the head between the rocker boxes I2 and I3. The width of the group of fins iswas great as can be conveniently obtained in view of the rocker box and port opening locations, and certain of the central ns are interrupted as at 25 in the region of the sparkplug openings 2l to permit of the insertion and withdrawal of sparkplugs. It will be seen that there lare no ns whatever extending circumferentially all the way around the circumferential cooling ns due in part to the cylinder head, as indicated in the plan view of Fig. 1. Thus, the lower wall of the head body is not unduly estiifened and, when the head is embracement of these ns is sufficiently small so that the above mentioned bursting stress due Y to the screw ioint oi the head upon the barrel is effectively taken care of without imposing undue strain in the fin segments.

In addition to the particular arrangement of cylinder fins upon the head, one of the primary features of the invention is the method of Vproducing the coolingv iins. It is contemplated that in practice, presuming for instance that a cylinc'arry iins having an approximate depth of 2" to 2/2, having a thickness of about als of an inch and having a space therebetween of about als of an inch, whereby there will be substantially sixteen ns per inch. In forming these fins by conventional milling operations, wherein the cutter is started at one end of the iin and is traversed across the work, great dimculty is experi- `enced due to the tendency of a thin milling cutter to drift from the` true path which it isintended `to follow and also the arrangement of direction of feed of the cutter is quite dilcult due to the irregular profile of the roots of the fins where the body of the cylinder head includes valve housings and other protuberances. The novel milling method evolved for this problem comprises the .progressive formation of the cooling ilns by plunging ganged milling cutters in a straight line into the head blank. the direction of feed of the cutters relative to the head or the head relative and kin forming the center iin, while over the rocker box, a full complement of cutters would be utilized at each station.

The result of the aggregate plunge vmilling operation produces a profile at the roots of the cooling ilns which has a scalloped appearance indicated at 36 and 38 in Figs. 6 and 5. The number of scallops and the difference in thickness of the head material effected thereby is obviously controllable by the number of stations set up and the diameter of the milling cutters used. For a practical design, however, the arrangement shown is deemed to be satisfactory and the actual local increase. in section and the increase in weight caused thereby is very small as compared with a head prole in which the envelope of the iin root shape comprises a smooth curve. However, after the initial plunge milling operations inV which the b ulk of material has ybeen removed in the der head may be made of' bronze, the head will Y to the cutters, being substantially normal to a .theseveral different stations `and directions of cutter feed to effect a proper profiling of the `iin roots. In Fig. 6 a portion of the head profile over a valve port housing is shown, while Fig. 5 shows the head prole in the region of the center of the cylinder head between the rocker boxes. Each center adjacent respective letters a to m inclusive represents the center location of the milling cutter spindle,v axis at the bottom of its feed with respect to the cylinder head, while the arrows extending from each such center indicates the radii of the particular milling cutters used for respective stations for the n roots :at which the sections at Figs. 5 and 6 are taken, In practice, each letter a to m inclusive will represent a milling cutter lspindle upon which a group of cutters such as 30 will bel assembled, the cutters having a variety of diameters on each spindle in accordance with the lateral prole to be formed at that particular station on the cylinder head, a typical profile being shown as the envelope of themilling cutters 30 shown in Fig. 2.

' For' certain of the fins, some of the cutting staor other heavy alloy, a weight reduction is permilling operations.

formation of the'ns, a further step of proling the fin roots may" be used, if desired, to smooth oi the cusps remaining 4from the plunge milling.

The milling of all fins at one time requires machines and xtures of great rigidity. In experimental tool setups, alternate cutters may be omitted and two passes made at each station to form all the ins, the second pass being made after temporarily filling the slots of the first pass with soft solder or other semi-plastic material.

Referring to Fig. 3, we show four. positions of the cutter gang 32 used in forming the horizontal segmental fins around the bottom of the cylinder head. In this operation, the same cutter gang may be used for a succession of plunges into the head material since the vertical profile of the ns throughout their arcuate embracement is uniform. For this operation we contemplate plunging the cutter gang 32 possibly three or four times throughout the extent of the segment and in then rotating the cylinder head about its own axis to clean the cusps remaining from the plunge By aseparation of the ends of the horizontal ns 2l and 28 from the surface of the end ns 23, as at 38, clearance is afforded for the cutter gang 32 so that only a small cusp d0 is left at the end of each iin segment. Such a cusp may be reduced in size by the use of a milling cutter of smallerv diameter thanI that shown.

As indicated in Figs. 1, 2 and 4, the exhaust Iand inlet ports I5 are provided with mounting faces 43 at the sides thereof for the attachment of intake and exhaust pipes. These may be swung farther around the cylindery to allow of increasing the member of pompadour iins 23. The top of leach rocker box I2 and I3' is provided with a mounting face 45 to which rocker box covers 46 may be secured. The ends of the rocker'boxes opposite from the port faces 43 are provided with openings bordered by pads 41 to which a' cover such as 48 (Fig. 4) may be secured which normally forms a terminal for the push rod and push rod housing extending inwardly from the cylinder head to the engine crankcase. If the cylinder head proper be made from bronze mitted by this construction since the covers 48 and 46A may be made from light alloys.

While we have'described our invention in detail inf/itsv present preferred embodiment, it-will be obvious to those skilled in the art, after understanding our invention, that various changes and modications may bemade therein without departingfrom the spirit or scope thereof. We

aim in the appended claim to cover all such modifications and changes.

What we claim is:

A cylinder head for embracement of and attachment to a cylinder comprising a substantially hemispherical dome, divergent integral rocker and valve port boxes extending outwardly fromthe body of the head in acutely angled relation to y head below said boxes over the top of the head 10 ns of the first plurality.

and between said boxes, said n plurality, at the head base, subtending substantially a quadrant of the head -base circumference, and second pluralities of parallel spaced ns in planes` normal to the cylinder axis and normal to the rst fins, extending around those segments of the head base below the rocker boxes and between the end fins of the first ln plurality, the ends of said second ns being free from contact with the end EDWARD C. STEINER. HENRY C. HILL.

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