US2364140A - Magneto - Google Patents

Description

Dec. 5, 1944. K. A. HARMON MAGNETO Filed May 13, 1942 4 Sheets-Sheet l Dec. 5, 1944.

K. A. HARMON 2,364,140

MAGNETO Filed May 13, 1942 4 Sheets-Sheet 3 INVENTOR ffZ'JVJVEIHA .fihlswazv BY ATTO EYS Dec. 5, 1944. HARMON 2,364,140

MAGNETO Filed May 13, 1942 4 Sheets-Sheet 4 mam;

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' detailed description UNITED STATES, PATENT OFFICE r. MAGNETO Kenneth A. Harmon, Longmeadow, Masa, assignor to Wico Electric Company, West Springfield, v

Mass, a corporation of Massachusetts Application May 13, 1942, Serial No. 442,737

"This invention relates to improvements in magnetos and more particularly to improvements in the construction of the magnetic field elements and the armature flux-conducting elements of the magneto.

The invention, in one aspect, is an improvement in the magneto shown in my prior United States Patent No. 2,233,946, granted March 4, 1941. That is, the invention starts with the same general arrangement of magnets, fiux-conducting members, and coils shown in said patent and modifies these elements to make the magneto better suited for use with airplane engines having a large number of cylinders.

One object of the invention is to provide an improved armature structure for a magneto of the type described, characterized in that the outer leg of each of the U-shaped, laminated, fiux-conducting members is divided into a plurality of branches, each provided with pole faces for cooperation with the pole shoes of a magnetic rotor, such pole faces being angularly spaced in a circular series about the axis of rotation of said rotor.

Another object of the invention is to rigidly fix these fork-shaped outer legs in the marginal wall of the magneto casing, whereb they serve to rigidly support and firmly brace the inner legs of the flux-conducting members, which inner legs pass through the coil and conjointly form a core therefor.

Another object of the invention is to provide an improved magnetic field structure for a magneto of thegeneral type described, such structure being characterized by an arrangement of pole shoes of the magnets of the magnetic rotor for cooperation with the pole faces of the fluxconducting members of the armature structure to provide for breaking the magnetic circuit at alternately relatively long and relatively short intervals and to accomplish this purpose without sacrifice in the amount of flux change. The flux changes, although produced at irregular intervals in the cycle of rotation of the'rotor, are

nevertheless substantially equal, whereby the sparks produced during each cycle of rotation are substantially equal in intensity.

These objects will best be understood as the proceeds and they will --be pointed out in the appended claims. I

The invention will be disclosed with reference to the accompanying drawings in which:

1 is a side elevational view, partl in sectionalong the line ll of Fig. 2, of a magneto embodyin the invention;

5 Claims. (Cl. 171-209) Figs. 2 and 3 are cross-sectional views taken, respectively, on the lines 2-2 and 3-3 of Fig. 1;

Fig. 4 is a fragmentary sectional view taken on the line 4-4 of Fig. 2;

Fig. 5 is a perspective view of one of the laminated, film-conducting elements of the stator; and

Figs. 6 t0 9 are fragmentary sectional views taken similarly to Fig. 2 but showing the rotor in four successive flux-changing positions.

'Referring to Fig. 1, the magneto includes a casing C made of non-magnetic material. This casing includes a tubular section l0 containing the stator and rotor of the magneto, and an enlarged tubular portion it which houses suitable breaker mechanism and a suitable distributor.

The section it! is closed at oneend by an end screws ii and which is adapted to receivethe wires which extend from the distributor to the spark plugs of the engine.

The distributor and the breaker mechanism may, for example, be of the type disclosed in the copending application of Robert V. Atwood and Sidney K. Smart, Serial No. 442,842, filed May 13, 1942. These elements are not shown or described herein in detail because the invention is primarily concerned with th armature structure and the field-structure of the magneto. The. cam which actuates the breaker mechanism is shown at I8 and-the distributor rotor is shown, in part at H]. The rotor is fixed to the cam and t. e cam is fixed on the splined outer end of the magneto drive shaft 20, being held in axial position thereon by a nut 2| which forces it against the innerrace of a ball bearing 22 and the latter against a flange-23 on shaft 20.

The drive shaft 20 is rotatablysupported in suitable bearings, such as the ball bearings 22 and 24. The bearing 24 is mounted as indicated in end plate [2. The bearing 22 is mounted in a hub 25 which is integrally connected to the casing section in by a series (fouras shown in Fig. 3) of arms 26. casing for any suitable driving connection with an internal combustion engine. connectionis shown in part by the gear 21 mounted on-shaft20 and the coupling 28 by means of which the gear may be .held on the shaft-in various positions 01' angular adjustment. A nut Shaft 20 extends outside the Such driving 23 clamps the gear and the coupling elements against the hub 30 and the latter against a flange 3| on the shaft. The casing C is adapted to be suitably secured to the crankcase of the engine with the gear 21 extending into such crankcase. A pilot flange 32 is provided on the end plate I! to enable the casing to be centered in the crankcase opening- The rotor of the magneto (Fig. 2) includes a circular'series of short bar magnets 33 of high coercive force and laminated iron pole shoes 34 and 35 therefor. These magnets and shoes are suitably clamped against a non-magnetic face plate 35 which is an integral part of the described hub 30, the latter being splined to shaft 20. As shown in Fig. 1, an annular ring 31 of nonmagnetic material is placed against the magnets and shoes on the side opposite from the face plate 38. Rivets 38, passing through the ring 31, the pole shoes, and the disc 36 clamp the parts in place.

Each pole shoe has an inner concave face located coaxially of shaft 20 and movable in close proximity to the outer convex face of each of a series (eight as shown) of inner pole faces 39, formed one on the outer end of each of a series of eight spokes 40 which radiate from a ring 4|, split at 42 to reduce flow of eddy currents. The spokes and ring are made up of laminations, suitably held together, as by rivets 43, each lamination having part of the pole face, spoke, and ring as integrally connected parts thereof. The pole faces 39 are of equal angular extent and equally spaced one from the next in said circular series. The ring 4| is mounted on one end of a composite core which surrounds shaft 20. The ring is held in proper angular position on this core by a key 44 (Fig. 2). One face of the ring abuts a washer 45' of rubber or the like and the washer abuts a shoulder 45 (Fig. 1) on such core. The other end of this ring is counterbored to receive a split spring ring 46 which snaps into a groove in the core, whereby thering is held in proper axial position thereon. Because the washer 45 is compressible, the ring 4i may be pushed back far enough to allow the split ring to be snapped into the groove in the shaft. Then the washer presses the ring back into the position shown. The pole shoes also have outer convex surfaces located coaxially of the shaft and movable in close proximity to each of an outer series (eight as shown) of pole faces 41 formed on laminated members 41. These pieces are of equal angular extent and equally spaced one from the next in said circular series.

The pole faces 39 and 41 are interconnected by a series of four laminated flux-conducting members. One of these members is shown separately from the magneto and in unmachined form in Fig. 5. Each such member is of substantially the shape of an inverted U, having inner and outer legs 48 and 49, respectively, located in spaced parallel relation and a cross bar portion 50 connecting these legs at one end. The outer leg 49 is bifurcated and formed into two branches These branches have parallel portions 41. Additional short laminations 52 are placed on each side of each branch 41 to secure the desired width of face for the pole face. The laminations are temporarily held together in any suitable way as by the rivets 53 indicated, and by brazing them together as at C is formed and are permanently held in the easing by being embedded in the metal of which 53. Four of the described members are arranged in the mold in which the casing the casing is formed. After the casing C is formed, the members 41 and 48 are machined I coils 55 and 56, respectively. These inner legs may be, and preferably are as shown, embedded in the nonmagnetic metal 51, or other material, of which case C is composed. The outer legs, which are fork-shaped, are embedded in the marginal wall In that encompasses the coils. The stem 49 of each fork-shaped outer leg, the plurality of branches 41 and the connecting parts 5| are all thus rigidly anchored in said marginal wall, thereby rigidly bracing and supporting the central composite core formed by the inner legs 48. The cross-connecting parts 50 of the fluxconducting members are preferably also fixed to the casing as by embedding them in the spokelike arms 26, thus assisting in the supporting and bracing of the core.

It will be noted that the pole shoes of the rotor are of two different kinds, namely, 34 and 35, which alternate in the circular series. The shoes 34 each have outer convex faces ofabout twice the arcuate extent of the inner concave face and larger in arcuate extent than the pole faces 41' or 39. The shoes 35 have concave and convex faces of nearly equal arcuate extent and of nearly the same arcuate extent as the pole faces 41 or 39. In the case of each shoe, whether 34 or 35, the convex and concave surfaces extend in opposite directions from a radial plane passing centrally through the body of the shoe. This arrange ment provides for alternate large and small angles between the convex working faces of successive shoes in the circular series and for alternate small and large angles between the concave working faces of these shoes. The arrangement is also such that, where there is a small angle between the adjacent ends of the convex surfaces of two successive shoes in the series, this is opposed by a larger angle between the adjacent ends of the concave surfaces of the same two shoes and vice versa. The arrangement is such that when the convex face of a shoe 34 or 35 covers a pole face 41, the concave face of the same shoe is out of covering relation with that pole face 39 which opposes said face 41. The pole shoes, constructed as described, provide for the making and breaking of the magnetic circuit at alternately long and short intervals of the rotation of the rotor. The particular example herein disclosed for illustrative purposes provides for the breaking of the magnetic circuit sixteen times per revolution of the rotor and these breaks occur alternately at 15 degree and 30 degree intervals.

The operation of the magneto will be described with reference to Fig. 2, supplemented by the fragmentary views, Figs. 6 to 9 inclusive. Assuming that the rotor is positioned as shown in Fig. 2 and is turning in a counterclockwise direction, flux from the north poles of the magnets passes from the concave faces of shoes 35 to the pole faces 39 and into the members 40 and ring 4|, thence through inner legs 48, across the crossconnecting portions 50 and back through the outbetween the pole faces 41 and 39. The magnets are then momentarily short-circuited. However, prior to movement of the rotor into this lastnamed position, the circuit of the primary coil will be closed and will remain closed during the interval when the bridging of the pole faces 4'! and 39 bythe shoes occurs. Thus, the flux in the first-described circuit is held without substantial change during the brief interval when the bridging occurs. Continued movement of the rotor will bring the parts into the position illustrated in Fig. 6, wherein the concave faces of shoes 35 have left the pole faces 39 and the convex faces of the shoes 3d have left the pole faces 4?, thereby breaking the"magnetic circuit, first above described, and establishing a circuit in an opposite direction. Flux then fiows from north poles of the magnets and shoes 35 to the pole faces 41',-

into the outer legs and across parts 50 into the inner legs 48 and thence to the members 40, pole faces 39 and the shoes and the south poles of the magnets. This position shown in Fig. 6 is a sparking position of the rotor and it will be understood that the primary circuit will then be opened. After the rotor has turned 15 degrees from the Fig. 6 position, it will be in another sparking position which is illustrated in Fig. 7. The convex faces of the shoes 35 of north polarity have left the pole faces 41' and the concave faces of these shoes have moved to connect with the pole faces 39. Theconcave faces of the shoes 34 of south polarity have left the pole faces 39 and the convex surfaces of these shoes have moved to connect with the pole faces 41'. The magnetic circuit through the coil is again reversed. It will be understood that the primary circuit will have been closed during the short interval in which the shoes 34 and 35 bridged acrossbetween pole faces 41' and 39 and that this circuit will be opened again when thero'tor is in the Fig. 7 position. After the rotor has turned 30 degrees from the Fig. 7 position, it arrives at another sparking position which is shown in Fig. 8. The shoes35 of north polarity then connect with the pole faces 47! and the shoes 36 of south polarity then connect with the pole faces 39. Thus, the magnetic circuit is again re-t versed. It will also be understood that the primary circuit was closed before the rotor moved into the Fig. 8 position and during the interval when the shoes bridged across between the pole faces ll" and 39. When the rotor is turned 15 degrees from the Fig. 8 position, it arrives at another sparking position which is shown in Fig. 9. The shoes 35 of north polarity then connect with the pole faces 39 and the shoes 34 of south polarity with the pole faces 41, whereby the magnetic circuit through the primary coil is again reversed. The primary circuit will have been closed prior to the time when the rotor reaches the Fig. 9 position and it will be opened at said position. A further 30 degree movement of the rotor will bring it into a sparking position similar to that shown in Fig. 6 and the described cycle of operations m'll be repeated. Thus, the magnetic circuit is broken at irregularly spaced intervals, herein shown as alternate 30 and 15 degree intervals and at each break a reversal of magnetic flux through the primary coil occurs.

The arrangement just described, whereby successivebreaks in the magnetic circuit are made at different angular intervals, is important and more particularly because sharp, clean, and effecpaced intervals, to be effected without any substantial sacrifice in the amount of the flux change. Each flux change is substantially equal and the sparks produced will equal.

The invention also provides an improvement in the armature structure of the magneto. The fiuxconducting members are so constructed as to provide the desired large number of pole faces in the outer circular series of the stator and they also provide a very effective bracing and rigid support for the inner legs of these members, which inner legs together form the core for the coils. The outer legs are more effectively anchored in the marginal wan of the casing than has been possible with any prior art structure of which I am aware, and because of this and because of the fork-shaped form of these legs, the core is firmly braced and rigidly held in position, even without the aid of the members 5i! which are preferably also embedded in the casing as shown.

Thus, I have provided improved magnetic field elements and improved flux-conducting members for the armature of a magneto, enabling the magneto to be used to advantage with airplane engines having a large number of cylinders.

What I claim is:

1. In a dynamo electric machine, a coil, a plurality of laminated flux-conducting members looped through said coil and having an inner and an outer circular series of pole faces angularly-spaced about the axis of said coil, and

a magnetic rotor having a circular series of angularly-spaced bar magnets coaxial with said inner and outer series and having pole shoes for said magnets, each said pole shoe having an outer face for cooperation with the pole faces of said outer series and an inner face for cooperation with the pole faces of said inner series, the outer faces of said shoes being angularlyspaced by alternately relatively long and relatively short distances and the inner faces of said shoes being angularly-spaced by alternately relatively long and short distances, each successive pair of shoes having their outer faces separated by a different distance thantheir inner faces.

2. In a dynamo electric machine, a coil, a plurality of laminated flux-conducting members looped through said coil and having an inner and an outer circular series of pole pieces angularly-spaced about the axis of said coil, and a, magnetic rotor having a circular series of angularly-spaced bar magnets coaxial with said inner and outer series of pole pieces and having pole shoes for said magnets, each said pole shoe having an outer face for cooperation with the I inner faces of the pole pieces of said outer setive breaks in the magnetic circult are obtained under such conditions. The arrangement enables ries and an inner face for cooperation with the outer pole faces of the pole pieces of said inner series, the shoes for each magnet having their outer faces separated by a different distance than their inner faces, one set of faces of the shoes of each magnet having their adjacent edges spaced apart by a distance less than the length of the magnet and the other set of faces having their adjacent edges spaced apart by a distance greater than the length of the magnet.

3. In a dynamo electric machine, a coil, a plurality of laminated flux-conducting members looped through said coil and having an inner and an outer circular series of pole pieces angularly-spaced by equal distances about the axis of said coil, and a magnetic rotor having a circular series of bar magnets coaxial with said be substantially being irregularly spaced by alternately relatively long and relatively short angles, a relatively short angle between the outer faces of two successive pole shoes being opposed by a relatively large angle between the inner faces of the same pair of shoes, and the long spacing between the corresponding faces of two successive pole shoes oeing' greater and the short spacing between the other faces of the same shoes being less than the angular spacing between a pair of,suc-' cessive pole pieces of the inner or the outer series, whereby when the outer :face of a shoe of one polarity connects with a pole piece or the outer s s the inner face of the same shoe and the outer face of the next shoe of opposite polarity will not connect with any pole piece of the inner or outer series while the inner face of shoe oi opposite polarity will connect with a pole piece of the inner series.

4. in dynamo electric machine, a coil, a plurality of laminated. flux-conducting members, each such member having an inner leg extending from one end face of said coil through the coil in a direction substantially parallel to the axis or the coil and beyond the other end face of the coil terminating at one end with a pole face, said legs and faces being angularly-spaced in an inner circular series about said axis, each member having a portion integrally connected to its other end and extending outwardly along and substantially parallel with and adjacent the first-named end face of the coil to and beyond the. periphery of the latter, and outer legs integrally connected to the outer ends of each said portion, the laminations of each outer leg being held together as a single group adjacent its connection with said portion and being divided at a point beyond said connection and spread apart into a pluralit of angularlyspaced groups forming branches, the constituent elements of each group being separately bound together, each branch being separated from the others by intervening non-magnetic material, each outer leg and its branches extending along and outside the periphery of the coil to and beyond the second-named face thereof and the branches terminating with pole faces, said branches and pole faces being angularly spaced in an outer circular series about the axis of said coil, and a housing or nonmagnetic material in which said outer legs are embedded with the material of the housing engaging both sides of each branch of each outer leg, and the inner legs being bound together into one core-forming unit, said unit being rigidly supported and ii-raced by the anchoring of the several branches or" each outer le the material of said housing.

In a dynamo electric machine, a coil, a plurality of flux-conducting members, each made up of a group of one-piece approximately U-shaped laminations, each member having an inner leg extending from one end face said coil through the latter in a direction parallel to the axis thereof and beyond the other end face thereof terrrdnating near one end with a pole face, said legs and faces being singularly-spaced in an inner circular series about said axis, each member having an outer leg formed by dividing its laminations at a point intermediate its ends and spreading the laminations apart into two separated groups forming al fork-shaped portion with a stern and two branches, each member having a cross-connecting portion extending outwardly adjacent and along the firstnamed end face of the coil and interconnecting the first-named end of its inner leg to the stem of its outer leg, said branches of each outer leg extending along and outside the periphery of the coil beyond the second-named end face of said coil and terminating with pole faces, said branches and pole faces being angularly-spaced in an outer circular series about the axis of said coil, a housing of non-magnetic material for said coil and members having an annular wall encompassing the coil and in which well all the branches of all the fork-shaped outer legs are embedded for the purpose of rigidly supporting and bracing the inner legs within said coil.

KENNETH A. HARMON.

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