US3396709A - Roto-piston engine - Google Patents

Description

3, 1968 w. J. RBICHEAUX 3,396,709

ROTO-PISTON ENGINE Filed May 9. 1966 6 Sheets-Sheet 1 13, 1968 w. J. ROBICHEAU* 3,396,709

ROTO-PISTON ENGINE Filed May 9, 1966 6 Sheets-Sheet 2 INVENTR. W4AENJ OBIC/'AUX Aug. 13, 1968 w. J. ROBICHEAUX ROTO-PISTON ENGINE 6 Sheets-Sheet 3 Filed May 9. 1966 Aug. 13, 1968 w. J. ROBICHEAUX ROTO-PISTON ENGINE 6 Sheets-She6t 4 Filed May 9, 1966 Aug. 13, 1968 w. J. ROBI'CHEAUX ROTO-PI STON ENGINE 6 Sheets-Sheet 5 Filed May 9. 1966 g- 1968 W!J. ROBICHEAUX 3,

ROTO-PISTON ENGINE Filed May 9. 1966 6 Sheets-Sheet 6 F.zg. 10

Unted States Patent O 3,396,709 ROT-PISTON ENGINE Warren J. Robicheaux, Port Arthur, Tex., assrgnor t o Gulf Oil Corporation, Pittsburgh, Pa., a corporatron of Pennsylvania Filed May 9, 1966, Ser. No. 548,570 9 Claims. (Cl. 123-45) ABSTRACT OF THE DISCLOSURE A number of dilerent engines, both four-cycle and two-cycle, which utilize a unitary double opposed pistons and cam wheel member are described. Means are provided to hold the edge of the cam wheel at two locations in the housing. The explosion of the fuel mixture against the face of one piston moves the associated member axially. The axial motion is simultaneously converted into rotation of the entire member by interaction of the rollers at the edges of the cam wheel.

This invention relates to a rote-piston cam engine, wherein the basic moving part is a piston-cam member comprising a geared cam wheel having a piston fixed to each of the opposing sides thereof, and which directly converts the reciprocatory translational motion of the member t0 rotational movement.

The piston-cam member allows more freedom in varying stroke t0 piston ratios, and produces engines with more horsepower per cubic inch displacement or pound of weight than conventional reciprocating piston engines. An overhead valve cam shaft is also provided for better valve action.

The engine can be operated as either a twocycle or a four-cycle engine, and when operated as a two-cycle engine, the piston opposite the power piston can act as a compresser supercharger.

In a conventional four-cycle reciprocating piston engine, each piston fires once for every two complete turns of the crank shaft. In the four-cycle engine of the present invention, each piston fires once for only one complete turn of the piston-cam member.

In an alternative embodiment of the invention, two additional piston-cam members are provided, making a total of four such members, and thereby providing an engine comparable to a conventional eight cylinder engine. This embodiment provides an even greater advantage in its horsepower or cubic displacement to weight ratio. Virtually any number of pistons, including one, could be provided. By changing the configuration of the geared cam wheel, more or less firings per revolution of the piston-cam member is possible.

In the accompanying drawings forming a part of this disclosure;

FIG. 1 is an end elevati0nal view of a first embodiment of an engine having four cylinders embodying the invention;

FIG. 2 is a top plane view thereof with the valves and valve lifting mechanisms omitted;

FIG. 3 is a crosssectional view taken on line IIIIII on FIG. 1;

FIG. 4 is a cross-sectional view taken on line IVIV of FIG. 3;

FIG. 5 is a prospective view of one piston;

FIG. 6 is a view similar to FIG. 1 illustrating a modified form of the invention;

FIG. 7 is a view similar to FIG. 1 illustrating another modified form of the invention;

FIG. 8 is a cross-sectional view through a drive shaft illustrating a modified form of the valve lifters, showing them set-up for four-cycle operation.

3,396,709 Patented Aug. 13, 1968 FIG. 9 is a partial-sectional view taken at right angles to FIG. 8, similar to one side of FIG. 3, and showing the modified cam lifter structure set-up for two-cycle operation; and

FIG. 10 is a view similar to FIG. 3 illustrating still another modified form of the invention.

Referring now in detail to the drawings, 10 designates a four cylinder four-cycle internal combustion engine embodying the invention. Engine 10 comprises a pair of end manifold plates 12 each carrying an intake manifold 14 and an exhaust manifold 16. The manifolds may be secured to manifold plates 12 by any suitable means. A valve lifter cover plate 18 is secured to the manifolds 14 and 16 by any suitable means.

Each manifold plate 12 is provided with a plurality of internal interconnected cavities 20 which are connected to a conventional cooling water system not shown. Manifold plate .12 is formed with intake ports 22 and exhaust ports 24 which communicate with the intake and exhaust manifolds 14 and 16, respectively. The innermost wall of each port 22, 24 is disposed at an angle to the direction of piston reciprocafion, as will appear more clearly below. Wall 22 is formed with a valve seat 23 and wall 24 is formed with a valve seat 25. Plate 12 is provided with walls 26, which each form substantially a right angle with each wall carrying a valve seat, to thereby form a combustion chamber in front of each piston, as is well known to those skilled in this art. Removably secured in a suitable opening in wall 26 is a conventional spark plug 28.

As is well understod in this art, an electrical system is provided, but is not shown for the sake of clarity. Similarly, carburetion, exhaust, and lubricating systems, and other auxiliaries are provided but are not shown.

Rotatably mounted in plate 12 are a pair of valve lifter shafts 30, each of which carries a pair of Valve lifter cams 32. Valves 34 each comprise a valve head 36 cooperable with valve seats 23 and 25 respectively, a valve stem 38 slidably mounted in a convenient portion of valve plate 12, a spring retainer plate 40 fixed to valve stem 38, and a valve stem tip 42 cooperable with the lifter cams 32. A spring 44 is mounted between plate 40 and manifold plate 12, and is arranged t0 normally urge each valve head 36 into seating engagement with its respective valve seat. Fixed to each Valve lifter shaft 30, between the cams 32, is a helical gear 46. Each pair of helical gears 46 are driven by a helical gear 48 mounted on main drive shaft 50.

Joined to the inside surface of each manifold plate 12 is a cylinder housing member 52. A suitable gasket 54 is interposed between member 52 and plate 12 which are joined together by conventional bolts 56 in the conventional manner to create a predetermined combustion chamber volume. Member 52 is formed with a plurality of interconnected cavities 58 which are also connected to cavities 20 and the cooling system for the engine. A main shaft bearing 59 is mounted in both plate 12 and member 52, and bridges the plane of their juncture. Each cylinder housing 52 is formed with a pair of cylinders 60.

Mounted on the inside surface of each member 52 is an inner cover member 62. Members 62 are in spaced relation to each other, but are interconnected by a continuous housing cover 64, and are. each secured thereto by means of bolts 66. Al] joints between inner cover members 62 and the members 52 and cover 64, as well as similar joints in the embodiments described below, are suitably gasketed by means not shown for the sake of clarity. Each member 62 is joined to its respective member 52 by a plurality of bolts 68. Member 62 is formed with an opening 70 in registry with cylinder 60. Each member 62 carries a main shaft bearing 72 in registry with the bearings 59. Shaft 52 carries a pair of iy-wheels 74, each of Which runs in a cavity 75 formed in each member 52 between the cylinders 60. Fly-wheels 74 may be omitted in certain size engines if desired, since the geared cam wheel may be heavy enough to also function as a fiy-wheel.

Mounted in each cover member 62, with one on each side of each cylinder 60, are four piston-cam plate supporting rollers 76. The rollers 76 of each cover member 62 are in facing relation to the rollers of the other cover member, thereby forming four pairs of rollers. Each two pairs of rollers 76 on each side of main shaft 50 are in equidistantly spaced relation to the center line of the facing pair of cylinders 60 in the two members 52 on that side of the main shaft.

Rotatably mounted by each such adjacent two pairs of rollers 76 is a rigid piston-cam member 78, each comprising a geared cam wheel 80. The plane of cam wheel 80 is disposed generally perpendicular to the axis of the two adjacent cylinders 60, but the wheel undulates peripherally in this axial direction, and is provided with a first pair of opposed high points offset by 90 from a second pair of opposed high points, each two adjacent high points being interconnected 'by a smooth fiowing curve. The pe- -ripheral edge of wheel 80 is provided with gear teeth 82. The side peripheral portions of cam wheel 80 is rotatably receved and held between the rollers 76, and the peripheral thickness of said cam wheel varies slightly around its circumference to achieve a smooth and uniform motion of the pistons, as will appear more clearly below. A piston shaft 84 extends through and is joined to the center of cam wheel 80. Thickened portions 86 are provided to rigidify and strengthen the joint between shaft 84 and wheel 80. Of course, these portions could be cast or forged or otherwise fabricated in one piece, if desired. A piston 88 is fixed to each end of shaft 86 and is slidably and rotatably received in cylinder 60.

Referring to FIG. 5, piston 88 comprises a plurality of sealing rings 90. The face 89 of the piston slopes outwardly and rearwardly and is provided with a plurality of forwardly extending fins 92. The front surfaces 93 of fins 92 are in a plane perpendicular to the axis of the piston. Since the pistons 88 rotate Within as vvell as slide Within cylinders 60, fins 92 create a greater turbulence Within the cylinder space during both intake of a charge and scavenging after firing. As is we known in this art, increased turbulence Within the combustion chamber is a greatly desirable advantage since such turbulence aids fuel distribution Within the chamber, lowers fuel consumption, increases efliciency and increases engine power.

Fixed to main shaft 50, between bushings 72, is a gear 94 which meshes with the gear teeth 82 on the two cam wheels 80.

The engine of the present invention can be made in a large range of sizes to almost any power requirements. The dimensional relationships Within the drive train can also be varied as required. However, for the sake of example, in the engine shown, the diameter of each cam wheel 80 is about twice that of gear 94. Cam wheel 80 will move each piston 88 through one stroke in a quarter revolution since it will move from the high point of one pair of high points to the high point of the adjacent pair of high points in 90. Therefore one complete four-cycle stroke, that is, intake-compression-power exhaust, of each piston will require one revolution of each cam wheel 80, and since each cam wheel carries two pistons, there will be a firing every 180 of rotation of the cam wheel. Because of the dimensional relationship mentioned above, each complete four-cycle stroke will therefore cause one complete revolution of :gear 94 and hence main drive shaft 50. Since each cylinder 60 has both an intake valve and an exhaust valve associated with it, and each valve must open and close once per complete four-cycle stroke of each piston, helical gears 48 and 46 are in a 1 to 2 diametric relationship.

The four-cycle internal combustion cycle is well known, but for the sake of illustration will be briefly explained as follows.

Referring to FIG. 3, the four cylinders are labeled A, B, C, and D for the sake of discussion. Starting from the position shown in FIG. 3 and assuming the engine is in continuons operation, cylinder A is about to begin exhausting a spent charge, cylinder B has just been fired, cylinder C has just completed an intake stroke and cylinder D has just completed an exhaust stroke. 90 of rotation of cam wheels later, in the direction of the arrows in FIG. 3, cylinder A will be completing an exhaust stroke, cylinder B will be completing its power stroke, cylinder C has finished a compression stroke and will be firing, and cylinder D will be completing its intake stroke. Another et rotation et the cam wheels 80 later, in the direction of the arrows in FIG. 3, cylinder A will be completing an intake stroke, cylinder B will be completing an exhaust stroke, cylinder C will be completing a power stroke, and cylinder D will be firing.

Thus, each power stroke causes 90 of rotation of the associated cam wheel 80 and therefore 180 of rotation of the drive shaft 50. T he power is transmitted to the gear 94 since the power of the exploding charge against the pis ton pushes the geared cam wheel against the two roller bearings on the side of the cam wheel opposite that piston. Since the cam wheel is smoothly sloped all along its periphery, it will roll against said pair of rollers 76, rotate about its axis, and thereby turn gear 94 180 for each power stroke. Thus, the reciprocatory translationl motion of the piston-cam member is converted directly into rotational motion, and the power is transmitted via the rotational motion to the drive shaft 50.

Referring to FIG. 6 there is shown an engine 10a which is similar to engine 10 of FIGS. 1 to 5, but modified for two-cycle operation. In the four-cycle engine described above each piston fires once for each complete turn of its associated cam wheel. The basic change in the embodiment of FIG. 6 is that one piston of each pair is converted to a supercharger or compresser for the other piston of that pair, and therefore the power piston of each pair fires twice for each revolution of its associated geared cam wheel since the suction stroke is eliminated. Of course, the timing of the valves is appropriately adjusted.

In place of the intake and exhaust manifolds 14 and 16, the supercha1ging cylinder 96 is provided with an intake manifold 98 and an exhaust manifold 100. Exhaust manifold 100 empties into a reservoir or compression bottle 102. The outlet end of bottle 102 is connected to an intake manifold 104 for the power cylinder 106. Cylinder 106 is provided with an exhaust manifold 108. The intake and exhaust valves for cylinders 96 and 106 are not shown, but are similar to these shown in FIG. 3. It will also be understood that the pair of cylinders associated with the piston-cam member on the other side of the engine has a similar manifold and compression bottle arrangement.

Assuming the engine of FIG. 6 is running continuously and the power cylinder 106 has just fired, the next 90 et rotation of the associated cam wheel will cause compression of a charge in cylinder 96 during that power stroke in cylinder 106. At the end of this first 90 of rotation, intake manifold 98 will be closed, the compressed but unfired charge in cylinder 96 will be released into the compression bottle 102 and the exhaust valve leading to exhaust manifold 108 for cylinder 106 will be opened. During the next 90 of rotation of this cam wheel, a fresh charge will be drawn into cylinder 96, and cylinder 106 will simultaneously exhaust the spent charge and take in a fresh already compressed charge from bottle 102. At the end of this second 90 of rotation the power cylinder 106 will be ready to fire again and the cycle will repeat. Within the cycle, the exhaust valve closes at the beginning of the compression stroke. The intake valve is opened just prior to the closing of the exhaust valve. The intake valve stays open for about 15 degrees of turn of the cam-wheel, which is long enough to equalize the pressure in bottle 102 and cylinder 106. T he piston then continues forward and further compresses the fresh charge. This arrangement allows for more charge volume under higher pressure With a lower compression ratio.

The engine of the present invention is very versatile. The piston stroke can be lengthened or shortened by changing the amplitude, that is, the distance from high point to high point, in the axial direction, on the geared cam wheel. The number of power strokes per revolution of the geared cam wheel can be changed by changing the undulations or number of cycles of curvature, that is, the number of high points on the geared cam wheel. R.p.m. can be changed by adjusting the gear ratio between the geared cam wheels and the main shaft gear, with appropriate adjustments for the valve lifters. Any number of cylinders, including one, can be provided, within the practical limitations of locating the associated gearing.

In FIG. 7 is shown an eight cylinder angine 1% which comprises four piston-cam members 78b showing the manifolding for four-cycle operation. Said manifolding comprises an intake manifold l4b suitably branched to feed each of the four cylinders at the end of the engine shown, and an exhaust manifold 16b similarly branched. The geared cam wheels 80b drive a main shaft gear 9%. The engine of FIG. 7 will greatly increase the horsepower per cubic inch of displacement, and horsepower per pound of Weight ratios, and would not excessively increase the space required for the engine. Engine 1% could be set up for two-cycle operaton by making changes similar to those described above for converting engine to engine 10a. It will be understood that those portions of the engine 1017 not shown in full detail in FIG. 7 are the same as the analogous portions described above, With obvious changes in the housing members, auxiliary systems, and the like to accommodate the two additional piston-cam members and the four additional cylinders.

While engine 1017 can be considered the equivalent of a conventional eight cylinder angine in that both have eight cylinders, the two engines are not otherwse comparable, in that in engine 10b there will be eight power strokes per revolution of the :geared cam wheel whereas in the conventional eight cylinder engine there are only four power strokes par revolution of the crankshaft.

Referring to FIG. 8, there is shown a modified valve lifter assembly 108 which replaces helical gears 46 and 48, valve lifter shaft 30, and cams 32. This alternative form of valve lifter -mechanism is functionally the same as the valve lifter mechanism of FIG. 3. Assembly 108 comprises four rings, 110, 112, 114, and 116. Each ring comprises a raised cam portion 111, 113, 115, and 117 respectively. The rings are fixed to the main drive shaft 50c by keys 118, or by any other suitable means. The outer peripheral face of each ring slopes inwardly, and the largest diameter of any one ring is Substantially equal to or less than the smallest diameter of the next preceding ring, whereby the four rings in combination describe the shape of a truncated cone in cross-section. The valve stems 38c in FIG. 8, or 38d in FIG. 9, have their respective working tips riding on one of the four rings. The angle of disposition of the peripheral surface of each ring is such that the axis of the valve stem will be substantially perpendicular thereto, so that the cam portions will move the valve stem the full height of the cam portion. It will, of course, be understoodthat the valve stems are suitably supported and spring loaded to the closed position in the manner shown in FIG. 3, or in any other suitable manner. The valve lifter assembly 108d et FIG. 9 is suitable for use With the two-cycle engine shown in FIG. 6, and the valve lifter assembly 108 of FIG. 8 is suitable for use With the engine of FIGS. 1 to 5, the difference hein-g, as is obvious, in the number of valves required, the timing of the valves, and hence the disposition et the cam portions on the respective rings.

In FIG. 10 there is shown a two-cycle valveless engine embodying the invention. Engine 120 includes four cylinder bodies A, B, C, and D. The cylinders are mounted on a pair of cylinder cover members 122, which are interconnected by a housing cover 124 and secured with bolts 126. Each cylinder cover 122 carries four cam wheel supporting rollers 128 arranged in facing relation across the space between the cover members, to provide four pairs of rollers, With two pairs on each side. of the main Shaft 130. Shaft 130 is supported centrally of members 122 by means of bearings 131. The two pairs of rollers 123 on each side of the main shaft are arranged in equidistantly spaced relation from the center line of the piston-cam member 132 for the two cylinders on that side. Similarly to the embodiments described above, each member 132 comprises a -geared cam wheel 134 provided With gear teeth 136 on its peripheral edge, which gear teeth mesh with a main gear 133 on shaft 130. A piston shaft 138 is fixed to and passes through the center of the cam wheel 134, and a piston 140 is fixed to each end of said shaf.t, and is slidably and rotatably received within the cylinders A and D in the one case, and cylinders B and C in the case of the second pistoncam member. The pistons 140 may be the same as pistons 88 of FIG. 5.

Each cylinder A, B, C and D comprises a cylinder body 142 having an enlarged inner cylinder portion 144 suitably flanged as at 146 for securing to the cover 122 by means of bolts 148. A sealing member 147, carrying sealing means 149 to permit passage of the main Shaft, protects the main shaft bearings 131 and may also seal this area for lubrication purposes. Member 147 is also held in place by bolts 148. The inner end of each cylinder is sealed by a suitable baflle 150 interposed between flange 146 and the cover, and also held by bolts 148. Sealing means 152 are provided in baflle 150 to rotatably and slidably receive piston shaft 138. Forwardly of inner cylinder portion 144 is an outer cylinder portion 154 provided with air cooling fins 156. The inside diameter of outer cylinder portion 154 is smaller than the inside diameter of inner cylinder portion 144 for a reason which will appear below. The outer end of each cylinder is closed off by a cylinder head or cover 158 which is held to the outer cylinder portion 154 by means of bolts 160. Cylinder cover 158 carries a spark plug 162, and the inner face of said cover is in a predetermined spaced relation to the working face of piston 140 when the piston is at the outer end of its travel to provide a combustion chamber therebetween, as is well known in the art.

Each cylinder is provided with an intake manifold 164 connected to an intake port 166 formed in inner cylinder portion 144. Outer cylinder portion 154 is formed with an exhaust port 168 mediately the ends thereof. An internal communicating port 170 joins the external end of inner cylinder portion 144 With outer cylinder portion 154. Port 170 is axially closely spaced to but axially rearwardly of exhaust port 168, for a reason which will appear below.

The cylinder firing sequence is A, B, D, C. In the position shown in FIG. 10, cylinder A is firing, and cylinder D is just completing scavenging a spent charge and is about to close port 170 to begin a compression stroke. Closing of port 170 creates a vacuum in the inner cylinder portion 144 of cylinder D, which vacuum will draw a fresh charge into said portion through its intake port 166. The piston in cylinder B is approaching the end of its compression stroke and will fire next. The piston in cylinder C is moving to the right in FIG. 10, and will first uncover its exhaust port 168 and shortly thereafrer uncover its communicating port 170 to admit a new charge which has been slightly compressed in the process in its inner cylinder portion. As is conventional in two-cycle engines, the inlet to inner cylinder portion 144 is provided with check valve or other suitable means to insure this slight compression et the new charge before it is admitted to outer cylinder portion 154. This 7 compressed charge entering the outer cylinder portion through the communicating port simultaneously charges the cylinder and aids in scavenging the spent charge.

Each cylinder fires once per half turn of its associated geared cam wheel.

As in the tour-cycle engine described above, efficiency over prior interna] combustion engines will be gained because of the reduction of friction, since there is basically only one moving part, the piston-cam member, which also reduces the work load per power stroke.

In engine 120 as well as in the engines of a.ll the other embodiments, a power stroke has to overcome the friction of only one additional piston, whereas in more conventional internal combustion angines each power stroke has to overcome the friction of three, five or seven additional pistons and their crank mechanisms. In the present invention, such crank mechanisms have been eliminated, since the piston-cam member couverts the reciprocation of the pistons directly into rotation.

While the invention has been disclosed in detail above, it will be understood that the embodiments shown are for purposes of illustration only, and the protection granted is to be limited only .by the spirit of the invention and the scope of the following claims.

I claim:

1. A four-cycle engine comprising a housing formed wvith a pair of opposed, symmetrically disposed cylinders interconnected at their inner ends by a central housing portion, a unitary double piston and guiding plate member consisting of a pair of piston members and a guiding plate portion with one piston member in each of said cylinders and With said guiding plate portion in said central housing portion, said piston members defining a pair of combustion spaces between their outer ends and said housing, respectively, and a central unrestriced space 13etween their inner ends, said central unrestricted space being further defined by portions of said cylinders and said central housing portion, said housing cmprising means cooperable With the outer faces of said piston members to urge said unitary member into reciprocatory axial motion within said opposed cylinders, means to convert the forces imparted to said (faces of said piston members t0 forces which rotate said unitary member about the axis of said unitary member and which permit simultaneous axial mofi-on thereof; said conversion means consisting of a plurality et guide rollers in said central housing portion cooperable with a smooth, continuons, undulating, peripheral portion of said guiding plate portion on both sides of said guiding plate portion and on opposite sides of the axis of said unitary member; said guide rollers defining planes disposed substantially perpendicular to the axis of said unitary member, the regions of engagement :between said guide rollers and said gtfiding plate portion being contained in said perpendicular planes and said peripheral portion being embraced between pairs et guide rollers of said plurality of guide rollers, and said guiding late portion being substantially contained in planes parallel to said perpendicular planes.

2. The combination of claim 1, and power transmission means in said housing, said power transmission means being located in planes perpendicular to the axis of said unitary member, and said guiding plate portion comprising means cooperable with said power transmission means.

3. The combination of claim 2, said housing comprising a shaft rotatably mounted therein, said power transmission means comprising a gear fixed to said shaft, and said cooperable means in said guiding plate portion comprising gear teeth in mesh with said gear.

4. The combination of claim 1, the distance in the axial direction between each two adjacent undulations of said guiding plate portion being substantially equal to the stroke of each piston member in its cylinder.

5. The combination of claim 1, and fin means on the face of each piston member opposite said guiding plate portion, said fin means extending axially outwardly of said face.

6. The combination of claim 1, the axial length of said unitary member between the outer faces of the two piston members being less than the internal axial distance between the outer ends of said two cylinders by an amonnt substantiafly equal to the stroke of one of said piston members.

7. The combmation of claim 4, a second unitary member in said housing, means forming third and fourth cylinders in said housing, the two piston members of said second unitary member .being axially and rotaably movable in said third and fourth cylinders respectively; and the axes of said two unitary members and said shaft being parallel.

8. The com bination of claim 3, the axis of said unitary member and the axis of said shaft being disposed in parallel relation, intake valve means and exhaust valve means for each of said cylinders, each of said valve means comprising a valve stem, a valve lifter cam shaft in said housing disposed perpendicular to the axis of said unitary member and said first mentioned shaft, valve lifter oams on said cam shaft in operative engagement With the ends cf said valve stems, and transfer means on said cam shaft and said first mentioned shaft to drive said cam shaft.

9. The combinaton or claim 3, the axis of said unitary member and the axis of said shaft being disposed in parallel relation, intake valve means and exharu3t valve means for each of said cylinders, each of said valve means comprising a valve stem, a valve lifter cam ring on said shaft for each of said valve stems, the tip of each valve stem being in operative engagement with its respective cam ring, and the largest diameter of each ring being adjacent to and substantially equal to the smallest diameter of an adjacent ring.

References Cited UNITED STATES PATENTS 1,813,259 7/1931 Schick 7456 X 2,473,936 6/1949 Burf0ugh 12345 1,127,267 2/1915 McElwain 12358 2,083,510 6/1937 Stig6Is 123-58 2,269,281 1/ 1942 MicheIl 123-58 2,352,396 6/1944 Maltby 123-45 X 2,983,264 5/1961 Herr-mann 123-58 WENDELL E. BURNS, Primary Examiner.

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