US2252276A - Air-cooled cylinder head - Google Patents

Description

I E. C. STEINER ETAL AIR-COOLED CYLINDER HEAD Aug; 12, 1941.

Filed June 10, 1939 3 Sheets-Sheet l INVENTORS ZIDWRD c. snwwk w E Y6. HILL Y E N R T T A 12, 1941- E. cvs TElNEl Q ETAL. 2,252,276

AIR- COOLED CYLINDER HEAD Filed June 10, 1939 3 Sheets-Shet 2 INVENTOR5 Emmy c: 11.1. BY H ATTORNEY- 12, 4 7 at. STElNER ETAL 2,252,276

' AIR-COOLED CYLINDER HEAD Filed June 10, 1939 3 Sheets-Sheet 3 Patented Aug. 12 1941 OFFICE Ant-cooLEn CYLINDER HEAD .Edward 0. Steiner, Hawthorne, and Henry 0. Hill, Montclair, N. 1., assiznorsto Wright Aeronautical Corporation, a corporation of New York Application June 10, 1939, Serial No. 278,416

8 Claims.

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

In the development of air-cooled, aircraft engines, 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 efiective pressure. With the increase in cooling fin 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 finned cylinder heads, and casting and pattern practice has been materially improved to, gainboth greater cooling fin area and greater strength. The limits of this practice are rapidly being approached and the present invention teaches a different mode of cylinder head construction in which either castings or forgings of stronger material are used and inwhicha great number of deep cooling fins may be machined thereon, the number and depth of the fins probably being greater than those capable'of being produced by any casting methods. In comiection with this problem, it is preferable to make'the cylinder head a unitary structure, incorporating therein valve seat openings, valveports, and rocker box housings, some of which form protuberances on the cylinder head which ordinarily cause great difiiculty if the complete machining of a cylinder head be attempted. This difficulty is attended, of course, by greatly increased cost or production.

An object of this invention is to provide amethod of machining deep cooling fins 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 fins 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 stresses set up when the cylinder head is attached to the cylinder barrel.

Further objects, and an amplification 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 cutters utilized in forming the cooling fins;

Fig. 3 is a section on the 3-3 of Fig. 2 showing diagrammatically the method of forming certain of the cooling fins;

Fig. 4 is a fragmentary side elevation of a part of the cylinder head showing the opposite side oi that indicated in Fig. 2, and

Figs. 5 and 6 are respectively sections on the lines 55 and 6-4 of Fig. 2 showingdiagrammatically steps in the process of machining the cooling fins.

In the several figures, the cylinder head indicated in the aggregate at It is initially formed posed at an angle to one another at opposite sides of the cylinder head the internal shape of which is substantially hemispherical as'shown at It in Fig. 5. The lower part of the interior of the head is threaded as at IQ for attachment to a cylinder barrel in the conventional manner.

The head is likewise provided with openings 2| .ior sparkplugs and it will .be apparent that the adapted for attachment to a cylinder barrel withvarious openings and parts thus far described may be readily formed by conventional machining processes.- The'head as shown is provided with a first plurality ofvertical cooling fins 23 which extend from the bottom of the head as at 24 in Fig. 6 upwardly and across the top of the head between the rocker boxes I! and IS. The width of the group of fins is as great as can be conveniently obtained in view of the rocker box and port opening locations, and certain of the central fins areinterrupted as at 25 in the region of the sparkplug openings 2| to permit of the insertion and withdrawal of sparkplugs. It will be seen that there are no fins whatever extending circumferentially all the wayaround the cylinder head, as indicated in the plan view of Fig. 1.

Thus, the lower wall of the head body is not unduly stifiened and, when the head is screwed upon a cylinder sleeve the bursting stress induced by the threaded joint would have the effect; of slightly stretching the bottom of the head wall without however transmitting stress into circumferential bands which would thus be likely to crack.

second and third pluralities 21 and 23 respectively of segmental cooling fins are disposed in planes normal to the cylinder axis around those parts of the bottom of the cylinder head not occupied by the vertical fins 23. The arcuate embracement of these fins is sufllciently small so that the above mentioned bursting stress due to the screw joint of 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 producing the cooling fins. It is contemplated that in practice, presuming for instance that a cylinder head may be made of bronze, the head will carry fins having an approximate depth of 2" to 2 having a thickness of about a; of an inch and having a space therebetween of about of an inch, whereby there will be substantially sixteen fins per inch. 'In forming these fins by conventional milling operations, wherein the cutter is started at one end of the fin and is traversed across the work, great difilculty is experienced due to the tendency of a thin milling cutter to drift from the true path which it is intended to follow and also the arrangement of direction of feed of the cutter is quite diflloult chines and fixtures of great rigidity.

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 fins 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 to 'the cutters, being substantially normal to a tangent to the blank at the poin of entry of the cutter gang. In Fig. 2 cutter angs are indicated at 30 and 32 respectively for forming portions of the fin groups 23 and 28. For forming the fin groups 23 reference may be made to Figs. 5 and 6 in which are shown by letters a to m inclusive the several different stations and directions of cutter feed to effect a proper profiling of the fin roots. In Fig. 6 a portion of the head profile over a valve port housing is shown while Fig. 5 shows the head profile 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 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 fin 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 spindle upon which a group of cutters such as 30 will be assembled, the cutters having a variety of diameters on each spindle in accordance with the lateral profile to be formed at that particular station on the cylinder head, a typical profile being shown as the envelope of the milling cutters 30 shown in Fig. 2. For certain of the fins, some of the cutting stations may be omitted; for instance, in Fig. 5 cutters would be omitted on stations 0, d, e, i, j and k in forming the center fin, while over the rocker box, a full complement of cutters would be utilized at each station.

The result of the aggregate plunge milling operation produces a profile at the roots of the cooling fins 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 ahead profile in which the envelope of the fin root shape comprises a smooth curve. However, after the initial plunge milling opera- :tions in which the bulk of material has been removed in the formation of the fins, a further step of profiling the fin roots may be used if desired to smooth oil the cusps remaining from the plunge milling.

The milling of all fins at one time requires ma- In experimental tool setups, alternate cutters may be omitted and two passes made at each station to form all the fins, 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 fins 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 milling operations. By a separation of the ends of the horizontal fins 21 and 28. from the surface of the end fins 23, as at 38, clearance is afforded for the cutter gang 32 so that only a small cusp 40 is left at the end of each fin segment. Such a cusp may be reduced in size by the use of a milling cutter of smaller diameter than that shown.

As indicated in Figs. 1, 2 and 4, the exhaust and 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 cylinder to allow of increasing the member of pompadour fins 23. The top of each rocker box 12 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 or other heavy alloy, a weight reduction is permitted by this construction since the covers 48 and 46 may be made from light alloys.

While we have described our invention in detail in its present preferred embodiment, it will be obvious to those skilled in the art, after underblank, the successive cuts of the cutter gangs being alined with one another to form fins continuous between one cut and the next, the roots of said fins being characterized by a scalloped profile due to successive cutter plunges.

2. The method of forming a narrow deep slot across an exteriorly curved metal blank which consists in laying out a plurality of spaced paths radiating from the proximate center of the blank, securing the blank for linear feed along respective lines, and in successively plunging and with- I drawing the blank along respective feed lines against a rotating slotting cutter, the bottom of of the blank, and in sequentially similarly plunging the cutter into the blank at spaced intervals therealong, the bottom of said slot having a scalloped profile due to successive spaced cutter cuts.

6. The method according to claim 5 with the further step of traversing a slotting cutter along the slot to remove the material forming the scalloped profile at the slot bottom.

7. The method of fabricating a plurality of parallel fins of substantially equal height extending along a solid metal blank of compound curved surface, which consists in arranging pluralities of individual cutters of different diameter on single spindles so that the envelopes of the cutter edges define curves substantially similar to the curves along successive zones of the blank surface, and in then successively plunging said slot having a scalloped profile due to successive cutter plunges into the blank.

3. The method according to claim 2 in which ganged slotting cutters are used to form spaced slots defining fins therebetween.

4. A method according to claim 2'in which ganged slotting cutters are used to form spaced slots defining fins therebetween, and in which the cutters of the cutter gang are of difierent .diameters to form slots of different depths.

5. The method of fabricating a relatively long and deep slot in a metal blank which comprises respective cutter gangs into the blank each in a direction substantially normal to the blank surface at respective zones.

8. The method of fabricating a plurality of parallelfinsof substantially equal height extending along a solid metal blank of compound face at respective zones, the individual cutters of the gangs being held in coplanar relation to corresponding cutters of other gangs to provide continuous inter-fin slots upon completion of the several plunges.

EDW. C. STEINER. HENRY C. HILL.

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