US 2272691 A
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R. CHILTON BARREL ENGINE Feb. 10, 1942.
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BARREL ENGINE Filed July 21, 1938 4 Sheets-Sheet 2 R. CHILTON BARREL ENGINE Feb. 10, 1942.
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Filed July 21, 1958 4 Sheets-Sheet 4 INVENTOR 1 @LH/VD CIJ/2701i ,v @J fa ATTORNEY\/ Patented Feb. 1Q, 1942 UNITED STATES BARREL ENGDVE Roland Chilton, Ridgewood, N.
J., assignor to Wright Aeronautical Corporation, a corporation of New York Application July 21, 1938, Serial No. 220,453
This invention relates in general to so-called "barrel engines, wherein cylinders are arranged around and axially parallel to a power shaft, and specifically to cam type engines wherein the driving connections between the pistons and the power shaft consists of rollers in the pistons and a cam rigid with the shaft.
'Ihe limit on size of aircraft is increasing at an accelerating rate as the art develops, so that the demand for power plant units of greater power than any available is becoming more insistent. Two main lines of development to satisfy this demand are:
(l) The development of cylinder units of much larger displacement than in current practice, for assembly on engines of conventional forms, in which 18 cylinders is the maximum that has yet been successfully used in the air-cooled radial types;
(2) Developing a form of piston-to-poWer-shaft mechanism which will permit the economical use of a much greater number of cylinders than 18 on a single power shaft.
Accordingly, a prime object of the invention is to develop a cam and roller type piston mechanism suitable for very large horsepower outputs, involving large cam diameter and a great multiplicity of cylinders.
The conventional construction comprises a power shaft carrying a face cam comprising a laterally waved rim having a diameter equal to the pitch circle on which the cylindersare disposed. Such a cam and shaft assembly is subject to end thrust from explosion loads which thrusts in the prior art have been taken on conventional thrust bearing means on the shaft. This involves bending moments acting at an arm equal to the radius of the cam. When a small number of cylinders is employed, the "arm and, accordingly, the bending moment, is small, with but a great number of cylinders, anda large cam, the bending moment becomes excessive involving very -great weight in the cam and its supporting structure. Accordingly, one of the important provisions of the present invention re sides in means whereby the axial cam reactions are transmitted to the main structure near the outside of the cam close to the point Whereat the pistons apply their working loads to this member. In this way, the bending or twisting moments on the cam and on the main engine structure are reduced to very small proportions.
The'present invention also includes novel cowling means for providing adequate cooling air flow for an engine having cylinders on both sides of 55 (Cl. 'I4-56) the cam i. e., a double .ended engine having front and rear assemblages of cylinders. The invention also includes improved piston and piston roller structure. Novel forms of manifolding, of supercharger disposition, of accessory drives, and many other objectives and advantages will be obvious from, or will be pointed out, in the following description with reference to the drawings in which:
Fig. l comprises longitudinal sections (on the line l-I of Fig. 2) whereof the upper half comprises a sectional plan on a plane passing between adjacent cylinders and the lower half a sectional elevation on a plane passing through the axis of a pair of opposed cylinders.
Fig. 2 is an end view with an upper segment C-C and lower segments E-E, F-F and D-D in section on the corresponding lines of Fig. 1;
Fig. 3 is an enlarged fragmentary section through the left hand lower quarter of Fig. 1;
Fig. 4 is a detailed section of a piston member;
Fig. 5 is a reduced scale view showing the cowling and air ow, and
Fig. 6 is a diagram further illustrating the novel cam supporting means.
Referring first to Fig. 1, I@ and l2 designates power shafts comprising two similar parts clamped together by flange joints It, at the center of the engine, which flanges secure a cam disc i6. The cam illustrated is of multi-lobe form, the lobes comprising a rim I8 integral with the disc I6 and having a sinusoidal form (as illustrated in development in the diagram, lg. 6) which form gives true harmonic motion to the pistons and accurate dynamic balance therebetween without recourse to counterweights such as are required with single lobe cams and in the slant or wobbler-crank types of mechanism.
The main cylinder carrying structure consists of housings 20 provided with power shaft bearings 22 and with circumferentially disposed cylinder decks 24 to which a large plurality of axially parallel cylinders 26 are secured as by ring nuts 28 (seen in the enlarged section of Fig. 3). The two main end housings 20, 2l) are secured into an intermediate drum member 30 by suitable circumferential screws 32 and, intermediate each pair of cylinders, by through bolts 35, seen in the upper intercylinder section of Fig. 1 and also in end view in Fig. 2.
Just beneath the cam rim I8, the cam disc I6 is provided with plane tracks 36 engaged by rollers 38 journalled in suitable bearings 40 rigid with the main housings as shown. The cam rim I8 is engaged on either side by piston rollers 42 supported on slipper bearings 44 carried in a piston connecting member or backbone" 46, secured at each end to pistons 48 by bolts 80 as best illustrated in the detailed view of Fig. 4. As seen in Fig. 4 and in the section E-E of Fig. 2 the rollers 44 are disposed in pockets at the ends of the member 46, which is cut away intermediate said pockets to clear the cam I8, as seen in the section F--F of Fig. 2. The surfaces 52 of the piston connecting member 46 are cylindrically finished to comprise extensions of the piston surfaces whereby they form piston guiding slippers sliding on the walls of the associated cylinders.
The novel cam support is illustrated diagrammatically also in Fig. 6 where in the piston rollers 42 will be seen straddling, and contacting respective faces of, the wave cam I8 whereas the supporting rollers 88, which are rigidly journailed in the main engine structure, engage the plane tracks 26 formed just beneath the cam. In this specific embodiment the width "W" of the cam element is less than one-half the stroke of the pistons wherefore some portions of the plane tracks 36 for the stationary rollers appear as full lines in this diagram.
It will now be seen that the main explosion forces from any one cylinder are transferred to the cam by the associated piston rollers and that the equal and opposing reactions are transferred by the adjacent stationary rollers 68 directly to the main cylinder deck elements 20 which are rigidlyy and directly secured against these loads by the through bolts 84. heavy sections required to transmit these loads are indicated by the cross hatching to |26 in Fig. l which will be seen to apply to only a local element of the main engine housing members 20 because the loads involved cancel out through the rollers 88. However, in conventional constructions where these thrusts are taken down to power shaft bearings as at 22, the loads are transferred from the cylinder decks radially inwards to the center of the member 20 and then radially outwards by the cam disc I6 whereby these members would become excessive in weight and in lateral bulk and, in fact, it is doubted if adequate rigidity could be provided with the radial dimensions involved in an engine having the number of cylinders here contemplated.
To each of the main housings 20 there is secured an accessory gear housing 54. Secured in turn to the accessory gear housings 54, are extension bearing members comprising tubular extensions 56 springing integrally from a flange member 68 which extends radially outwards to effect said securement as by screws 60. 'I'he flange element 58 includes mounting pads for the various engine accessories such as a starter 82, a generator 64, air pump 66 and magnetos 86 etc. (See Fig. 2.)
The power shafts I0 and I2 are illustrated in the preferred double ended disposition wherein the power take-oil extensions extend from respective `ends of the engine, permitting the use of tandem propellers by suitable extension shafts. It will be seen that the entire design is symmetrical about the mid-plane, so that any unit may be turned end-for-end at installation giving reverse rotating propellers as is often desired in multi-engine installations, and thus avoiding the complication of building right and left-hand rotation engines for this purpose.
While any form of cylinders and valve gear may be used with this type of engine, the preferred embodiment is one wherein the cylinder assemblages have opposite lateral sides free of projections beyond the normal cylinder barrel fins. This is because the engine diameter for a given number of cylinders is controlled by the closeness of 'the circumferential cylinder spacing which can be obtained. The rotary valve cylinders of my copending application, Serial No. 182,456 filed December 30, 1937, have this desired characteristic and, accordingly, are illustrated. This cylinder disposition is such that inlet port elbows 10 and exhaust elbows 12 may be disposed on the inner and outer sides of the cylinders respectively, as shown, to connect to annular intake manifolds 14 and annular exhaust collectors 16 respectively. This disposition affords a free air flow to the cylinder fins which flow is induced and guided by novel cowling now to be described.
Referring to Fig. 5 the engine is provided with a front cowl 16 enveloping the front exhaust manifold 16 and the forward row of cylinders, and with a rear cowl 60 enclosing the rear exhaust collector. Between these two cowls is an intermediate cowl 62 which is overlapped by the trailing edge of the front cowl 18, to define a front exit 64, and which overlaps the rear cowl to define the rear exit slot 66. It will be seen that the air flow to the front cylinders enters the forward open end of the front cowl 18, passing within the inlet manifold 14 whereby the only path of exit is by way of the cylinder fins. As will be clear from the end view of Fig. 2, the fins of adjacent cylinders are practically touching so that pressure cooling is obtained with a minimum of bathing. However, the cowlings 16 and 80 have inturned extensions 8i!` close to the fins of the cylinder heads and a space is left between the Cowling and inlet manifold 14 whereby air also impinges directly upon the cylinder heads and flows radially outward through the cylinder head fins. Air for the rear cylinders is obtained from suitable forwardly facing scoops. In the case of a conventional nacelle arrangement shown in Fig. 5 these entrances are indicated at as being formed in the leading edge 92 of the airplane wing into which the cowl 80 merges as shown.V The wing will have a suitable partition 94 enclosing a space 96 to comprise an air pressure compartment from which the air can only escape past the fins of the rear cylinders into the rear exit slot 86, as previously described.
Each inlet manifold 14 is connected to a side type supercharger 98 by a suitable duct |00, Figs. 1 and 2. The exhaust'manifolds 16 are formed in two semi-circumferential portions starting from the cylinders on either side of the supercharger connection |00, in order to afford clearances therefor, and terminating in suitable tail pipes |02. The supercharger is driven by a radial shaft |04 enclosed in a suitable slender housing adapted to pass through an intercylinder space and furnished at its inner end with a bevel pinion |06 engaging a bevel gear |08 suitably driven from the power shaft. Similar radial intercylinder shafts may be used to drive other accessories. For instance, a radial shaft indicated by dotted lines at I|0 in Fig. 3 may be used to drive an oil pump unit H2 suitably connected to an oil sump H4 as indicated.
The rotary valve per se is not a part of the present invention which, however, provides a preferred form of valve driving mechanism comprising inclined shafts H6 each having a pinion ||8 at its upper end engaging a valve driving gear |20, arid splined at its lower end into a pinion |22 engaged with a master bevel gear |24 driven by the main shaft I0.
This disposition and the special conformation of the inlet elbows 10 and the disposition of the accessories affords ladequate area for free air flow into the pressure chamber embraced within the circle of cylinders at each end of the engine.
Attention is now called to an important and basic difference in the distribution of the inertia loading as between engines of the cam type here indicated and the conventional master rod arrangement as used in radial engines. Both these mechanisms are constructions whereby a multiplicity of cylinders may be eifective on a single crank throw or power shaft. In the case of radial engines, the largest number of cylinders in practice connected to a single crank is nine, giving the radial engine an important weight advantage over inline types, of which the V type is the best known having only two cylinders per crank throw.
` The cam engine carries this weight saving much further than in the radial type. In the example shown in the drawings, fourteen cylinders per end are indicated land the diameter over the cylinders is substantially less than would occur with nine cylinders of equal size in the conventional radial disposition. At the same time, with fourteen cylinders, it will be seen that room is afforded for disposing the various engine accessories around the power shaft at either end of the engine while still maintaining adequate area for cooling air fiow.
One of the basic considerations limiting the number of cylinders which may act on a single crank in the conventional radial disposition is that the inertia loads of all the pistons and their rods act cumulatively on the common master rod bearing so that the load thereon goes up with the number of cylinders. In the cam type engine, on the contrary, the loads of individual piston units devolve upon the individual piston -rollers and.
on the separate zones of the cam contacted thereby. It therefore follows that the contact loads on the'cam and piston rollers are quite independent of the number of cylinders used, thus the duty and pressure intensities on the cam tracks are determined by the explosion forces and the inertia forces of a single piston element and are not a function of the number of cylinders which, from this point of view, may be increased indefinitely.
The inertia forces subtract from the explosion loads so that it may be stated that the ideal combination is one in which the inertia forces acting on any one reciprocating element is one-half of the explosion force to which it is subject whereby the force actually reaching the cam is only onehalf of the gross piston pressure. With the double ended arrangement here shown, the reciprocating weights of the paired pistons, backbone and roller units are such that the inertia force reaches one-half of the main explosion force at a desirable engine operating speed.
As pointed out before, the multiple lobe cam disposition has the added advantage of comprising a reduction gear effect whereby the pistons may make four or six strokes per shaft revolution without recourse to reduction gears as needed in conventional engines to obtain the slow speed rotation necessary with large diameter propellers, as required for the high horsepower outputs here contemplated. A further advantage of multiple lobe harmonic cam disposition is that it affords an inherently balanced piston system free from the aberrations of conventional master rod systems while, at the same time, avoiding the necessity for the heavy counterweights characteristic of the radial types of engine. A further and important weight reduction results from the compactness of the design due to the cylinder disposition whereby a relatively large number of cylinders may be disposed within much smaller overall dimensions than in conventional types. For large engines, however, the most important weight reduction results from the extremely short stress path resulting from the novel disposition of this invention whereby cam reactions are taken back directly to the cylinder decks through thrust means disposed at the outer radius of the cam.
While I have described my invention in detail in its present preferred embodiment, it will be obvious to those skilled in the art, after understanding my invention, that various changes and modifications may be made therein without departing from the spirit or scope thereof. I aim in the appended claims to cover all such modications and changes.
I claim as my invention:
l. An engine including in combination, a power shaft, cylinders disposed around and parallel to said shaft, pistons arranged for reciprocation in said cylinders, a web member secured to said shaft having torsional rigidity, a rim on the member having a track undulating vaxially of said shaft to comprise a cam, rollers in said pistons straddling said cam track, an engine housing secured rigid with said cylinders, plane tracks on,
said rim disposed circumferentially close to said cam tracks and cam thrust means engaging said plane track and rigidly supported in said housing close to said cylinder securement.
2. In an engine in combination, a cam rim having circumferential tracks respectively plane and undulated, rollers engaging respective tracks, a
. piston member operated by said cam engaging rollers, a housing rigidly mounting the other said rollers, cylinders for said pistons rigidly secured to said housing, a central shaft, and a torsionally rigid web extending radially inward from said rim and secured to said shaft.
3. In an engine in combination, a power shaft, a web extending radially therefrom, a circumferential cam rim of substantially constant radius at the web edge and waved axially of said shaft and plane circumferential tracks close to said cam, rollers engaging said plane tracks, cylinders disposed about the shaft, pistons in the cylinders operated by said cam, bearing means for said rollers, securing means for said cylinders, and a housing rigidly uniting said bearing and securing means.
4. In an engine, a power shaft, cylinders spaced therearound on a given circumferential envelope,
la web member having a rim of corresponding circumference to the cylinder envelope comprising plane and axially waved tracks, a housing carrying said cylinders, and thrust means carried by said housing and engaging said plane tracks.
5. In an engine in combination, a housing, opposed cylinders circumferentially disposed therearound, pistons in each cylinder, a piston member rigidly uniting the opposed pistons to comprise unitary pairs, rollers in said piston members, a cam rim straddle by said rollers, plane tracks formed on and rigid with said rim circumferentially disposed, thrust means engaging said plane tracks, a housing carrying said thrust means and cylinders, a web extending inwardly from said rim, a central shaft secured to said web, and bearing means in said housing for said shaft, said bearing means being free of thrust loads imposed on said rim.
6. A drive member for a barrel engine comprising a. central shaft, a substantially plane torsionally rigid disc secured thereto, a rim at the edge of said disc comprising circumferential tracks respectively plane and axially waved, a housing carrying said drive member. thrust means on the housing engaging said plane track, cylinders secured to the housing adjacent said thrust means, and piston members reciprocable in the cylinders engaging said waved track.
7. A drive member for a barrel engine corn-I prising a straight shaft, a torsionally rigid but axially yieldable web disc thereon, and a rim at the disc periphery comprising plane and axially waved tracks concentric with the shaft.
8. A drive member for a barrel engine cornprising a straight shaft, a torsionally rigid but axially yieldable web disc thereon. and a rim at the disc periphery comprising plane and axially waved tracks concentric with the shaft, the engine comprising a housing having circumferentialiy disposed thrust means engaging the plane track and thrust producing means engaging the waved track.
9. A drive member for a barrel engine comprising a straight shaft, a torsionally rigid hut axially yieldable web disc thereon, and a rim at the disc periphery comprising plane and axially waved tracks concentric with the shaft, the engine comprising a housing having circumferentially disposed cylinders axially parallel tc the shaft, a piston member in each cylinder having driving engagement with said waved cam, and n plurality of thrust devices in the housing adjacent and between the several cylinders engaging said plane track.
l0. A drive member for a barrel engine comprising a straight shaft, a torsionally rigid but axially yieldable web disc thereon, and a rim at lil the disc periphery comprising plane and axially waved tracks concentric with the shaft, the engine comprising a. housing having circumferentially disposed cylinders axially parallel to the shaft; a piston member in each cylinder having driving engagement with said waved cam. and a plurality of thrust devices in the housing adjacent and between the several cylinders engaging said plane track, there being an equal plurality of relatively staggered cylinders and thrust devices whereby thrust force from each piston and cylinder reacts through the two thrust devices on each side thereof.
11. In an engine, a power shaft, a disc member thereon having a rim comprising plane and waved tracks, disc-like housings on each side of said disc, clrcumferentially spaced rollers on each housing engaging the plane track of said rim, cylinders axially parallel to the power shaft secured to the housings, and piston members reciprocable in said cylinders having rollers engaging the waved track of said rim.
12. In an engine, a power shaft. a disc member thereon having a rim comprising plane and waved tracks, means drivably connecting said rim and shaft, thrust producing means engaging said waved track and imparting driving torque to the rim. and reaction means engaging the plane track isolating certain of the thrust forces from transmission to the disc and shaft.
13. In an engine, a shaft, a cylinder axially parallel thereto and spaced therefrom, housing means securing the cylinder and comprising a hearing for the shaft, a rim concentric with the shalt comprising an annular plane track and an annular axially waved track, piston means reciprocable in the cylinder engaging said waved track for imparting thrust thereto on a line substantially coincident with the cylinder axis, reaction means engaging the plane track secured to the housing adjacent said cylinder, and a torsional driving element connecting said rim to said shaft.
A ROLAND CHILTON.