US2354302A - Magneto unit - Google Patents

Description

Patented July 25, 1944 MAGNE'ro UNIT Wilbur L. Carlspn, Rochester, N. Y., assigner to General Motors Corporation, Detroit. Mich.. a

corporation of Delaware Application August '7, 1941, Serial No 405,143

13 Claims.

This invention relates generally to the construction of magneto units and more* particularly to certain featuresof construction which are of general use butespecially desirable for use in units for airplane engine ignition.

Considerable trouble has been encountered since the advent of relatively high altitude flying with magneto units which may operate satisfactorily at low altitudes but which either fail or operate erratically at high altitudes.

It has been found that Qne of the principal reasons for magneto failures and improper operation at high altitudes is due to the fact that as the density of the atmosphere decreases as an airplane ascends the dielectric strength of the rareiied atmosphere decreases to such an extent that the ignition spark in the distributor of the magneto unit which should jump successively from the rotary distributor arm to the spaced distributor points or electrodes will ilash or arc over the gaps between several of the distributor points simultaneously and thus cause improper firing of the engine cylinders.

One of the objects of this invention is to overcome this defect in prior units by providing a unit construction in which the distributor is located within a separate chamber which is entirely sealed against the entrance of external air so that theproper spark distribution to the cylinders is not affected by changes in atmospheric conditions on changes in altitude.

- A further object is to provide in such a con- A further object of the present invention is to provide a construction affording. a more completely insulated path for the high tension current with a proper spacing of those parts of the magneto unit that are' of widely varyingl potential.

struction a sealing means for the rotary drive connection to the distributor arm in which the efllciency of the seal increases with decrease in density of the atmosphere at higher altitudes to prevent leakage and thereby maintain the distributor chamber substantially at the atmospheric pressure of lower altitudes or ground level.

As will be described more fully hereinafter it is also contemplated that the sealed distributor chamber may, if desired, be maintained above the atmospheric pressure at ground level and charged with some medium other than air such as an inert gas to reduce the extent of corrosion of the distributor points and increase the breakdown voltage.

In addition to improper cylinder firing at relatively high altitudes there have been instances where the ignition has failed completely because of electrical breakdown and undesired grounding of the current conducting means extending from the high tension coil terminal to the distributor arm.

Other objects andy advantages of the present invention will be apparent from the following description of the embodiment illustrated in the accompanying drawing, in which:

Fig. 1 is a side elevationof the complete magneto unit with parts broken away and parts in vertical section.

Fig. 2 is a fragmentary front elevation of unit of Fig'. 1 on a slightly reduced scale.

the

Fig. 3 is a fragmentary' vertical section of the sealing means on a slightly enlarged scale.

Referring first to the showing in Fig. l, only those parts essential to an understanding of the features of construction of the present invention have been illustrated in detail and those parts not so illustrated may be of any desired conventional construction.

It will be understood, for instance, that the portion of the casing `indicated at 4 isadapted to house a generator with the usual stator and a rotor having a shaft 6 with one end thereof projecting outside the casing and adapted to be connected to and driven by the engine. The stator includes vertically extending spaced poles 8 which engage the opposite ends of the core of the induction coil I0 having primary and secondary windings. The primary windings are periodically opened by an interrupter mechanism which may be located within the portion of the casing indicated at I2 and operated by an extensionof the rotor shaft and the secondary windings furnish the high tension ignition current which is supplied to the engine through the distributor mechanism to be hereinafter described.

In accordance with the present invention the distributor per se is located within a completely sealed and insulated chamber indicated generally at Il which is formed primarily by the parts I6 and i8 of molded insulation material such as Bakelite. The spaced distributor points or electrodes 20 may consist of metal inserts in the molded part i6 with such points arranged, if desired, as shown in two parallel arcuate rows in the upper half of the distributor chamber with bores 22 to receive the separate conductors leading to the respective spark plugs of the engine. The other molded part I8 is adapted to close one end of part, IB and is shown as having molded therein a metal insert 24 with a bore 26 to receive a conductor providing for the use of a booster magneto or other external current source, if desired, as auxiliary ignition for starting puroses.

p Considering now the rotating parts of the distributor mechanism, a rotor 28 has been shown with a distributor arm 30 cooperating with one row of distributor points 28 and a distributor arm 32 cooperating with the other row of distributor points 20. As will'be more fully described hereinafter, arm 30 is connected to the high tension Winding or coil to furnish the primary ignition current and arm 32 may be connected to the booster magneto or external current source for starting.

It should be understood that in accordance with known practice wherein the distributor points are arranged in parallel arcuate rows, arms similar to 38 and 32 but cooperating with adjacent rows oiv distributor points are located on the distributor rotor 28 diametrically opposite the arms shown in Fig. 1 and the respective pairs of arms 30 and 32 may be slightly angularly spaced to provide a retarded spark for starting. Since this known arrangement constitutes no part of the present invention it is not considered necessary to provide any further disclosure thereof but it should be noted that the showing in Fig. 1 is not a true vertical section through the distributor rotor 28 insofar as the relative angular location of arms 3U and 32 is concerned.

The distributor rotor 28 is shown as being formed of molded insulation material with the distributor arm 32 consisting of a metal insert therein, and with the distributor arm 30 riveted to a metal bearing housing 34 and also constituting metal inserts in the rotor. The arm 32 is connected by means such as bolt 88 to ametal strap 38 on the molded insulating member 48 which is secured to the rotor 28 by such bolt. The strap 38 extends to the axis of rotation of the distributor rotor and is located at this point suiiciently close to the metal insert 24 to provide for the transmission of the booster ignition current to the distributor arm.32.

The bearing housing 34 is secured to the inner end of a drive shaft 42 which extends from this connection to the distributor rotor through a sleeve 44 which is preferably molded as an insert in the part i8 and extends on both sides of the wall of this part opposite the part I8. The outer end of shaft 42 is enlarged as at 48 to provide for the connection thereof to the drive gear 48 and to receive the shaft sealing means to be hereinafter described. 'I'he gear 48 which is formed of suitable insulating material meshes with a gear 50 of similar material which is mounted on the magneto rotor shaft 8. A metal bearing housing 52 is molded as an insert in gear 48 and this bearing housing 52 and the bearing housing 34 in distributor rotor 28 receive the outer races of the spaced antifriction bearings 54 with the inner races thereof mounted adjacent the ends of the stationary sleeve 44.

The outer end of shaft 42 is formed with an axially extending recess to receive a spring pressed contact member 58 which is adapted to contact with the terminal 58 of the high tension winding of coil I to conduct the high tension ignition current to the distributor arm 80.

The shaft sealing means which is indicated generally at 88 in Fig. 1 and shown in detail in Fig. 3 functions to prevent the entrance of air to the distributor chamber through -the space which would otherwise exist between the Guter end of shaft 42 and sleeve 44. The outer end of the sleeve 44 is provided with the stationary seal ring 82 which is adapted to be engaged by the rotating seal ring 84 secured by a sleeve 88 to a laminated flexible diaphragm 88.

The outer edge of this diaphragm 88 is secured within the bearing housing 52 between a flange 88 on such housing and the enlargement 48 on shaft 42 with the outer bearing race 18 and a member 12 functioning as spacers between the diaphragm and the ange on the bearing housing. A securing means such as the externally threaded nut 14 is provided to both clamp the diaphragm 88 between member 12 and shaft enlargement l48 and to secure the gear 48 nonrotatably to the shaft 42. As shown in Fig. 3, the nut 14 is threaded Within the outer end of the bearing housing 52 with a key 18 interlocking between a recess in the outer face of shaft enlargement 48 and a notch 18 in housing 52 and with a washer 80 having a bent lug 82 to engage in an opening in key 18 and also having a portion 84 which may be bent within the nut I4 to prevent relative rotation of the latter after assembly.

The engaging surfaces of the seal rings 82 and 84 are highly finished and the ring 84 is maintained in sealing contact with the ring 82 by the spring 88 which may assume any form but is illustrated as a thin disk of spring metal having fingers or prongs bent out therefrom.

With reference to the foregoing description, it will now be apparent that a completely insulated and sealed chamber has been provided for the distributor with a sealing means for the distributor drive shaft which extends outside of the chamber. In stating the objects of the present inventionV it was mentioned that the sealing means is so constructed and arranged that the eiilciency of the seal increases with decrease in density of the atmosphere at higher altitudes. This desirable result is obtained since on reference to the showing in Fig. 1, it will be seen that the space within the distributor chamber is in communication through the clearance between shaft 42 and sleeve 44 with the side of the seal diaphragm 88 on which the spring 88 is located so that any pressure of the air or gas to be referred to hereinafter in the distributor chamber is operative in the same direction as spring 88 to i'orce the seal ring 84 against the seal ring 82. Even though the pressure within the chamber may be only substantially atmospheric pressure at ground level it will therefore be apparent that at relatively high altitudes when the external air pressure decreases the resulting differential in pressures within and outside the distributor chamber which are effective on opposite sides of the seal diaphragm will cause an increased pressure contact of the sealing surfaces of the seal rings 82 and 84.

It was also mentioned in stating the objects of the present invention that the sealed distributor chamber may, if desired, be maintained above the sages such as i! and 94 in the molded part Il with the interior of the distributor chamber I4. 'Do prevent any leakage adjacent the valves it is apparent thatthe valve casings could, if desire-..

bemoldedasinsertsinthepartltandextend 6 outwardly through the cover .I or terminate within the cover and be accessible on removal thereof. 4 o' The ,details of construction of the valves may conform to any standard valve and are not cssenl tial to an understanding of the present invention. andinfactordinarystopcocksmayevenbe employed instead of valves. If, however.v air or gas under pressure is to be maintained within the the form of a pressure relief or regulating valve. If it is desired to charge the chamber witli an inert gas such as carbon dioxide (CO1) which has been found to be a very satisfactory medium, the

gas would be introduced under pressure through l tributing mechanism having a rotatable distribone valve while the other valve would be opened or so constructed as to function as a bleed outlet opening to ensure that all air is cleared from the chamber. Such valve or bleed opening would of course be closed as soon as the chamber is filled with gas.

It is also contemplated, although not shown in the drawing, that a source of air or gas under pressure such as a small bottle or container of compressed air or gas could l associated. if de- 30 sired, with the distributor chamber to take care of any minor leakage of air or gas from the chamber. l

With reference to the current conducting means extending from the high tension coil terminal to heretofore been the practice to either construct 4 the shaft of insulating material around a centralcurrent conducting rod or insulate the shaft from its bearings and other adjacent parts, and there have been many failures of this insulation. l As appears in Fig. l, no attempt is made to-i insulate the shaft 42 from the bearings 54 or adjacent metal parts such as sleeve 44 but the construct on is such that high tension current may be carried and be present in all of the metal parts adiaccnt to the shaft 42. Since gear 48 and parts 50 i6 and Il of the distributor chamber are constituted by molded insulation material it will be apparent that in the construction disclosed herein there is no meta-l part or point at ground potential close to any part of the huh tension circuit,

and therefore the chance of electrical breakdown is considerably reduced if not entirely eliminated.

Other features of the present construction together with the advantages thereof will be obvious to those skilled in the art. It will be apparent,

for instance, that the sealing means for the distributor drive shaft is located within the bearing housing 52 outside of the distributor housing and that a floating mounting of the distributor shaft 42 in the sleeve 44 is provided by the bearings I4 05 which are relatively widely spaced by reason of their location adjacent each end of the sleeve.

In certain prior constructions wherein the distributor arms constitute inserts in a. distributor rotor of molded insulating material it has been found that such material tends to become unstable and yield or give under the relatively high ambient temperature conditions encountered l during'operation and it is therefore diincult4 to tween the distributor arms and distributor points to provide the proper spark gaps at all times. In the present construction it will be seen that lthe distributor arms Il for the primary ignition current are secured, as heretofore described. directly to the metal bearing housing I4 which is in turn secured directly to the distributor shaft 42 so that even though the anns .30 constitute inserts in the molded rotor Il, such arms are so mounted as to prevent-,any radial displacement thereof. y

It should be understood that although but one 'embodiment of thepresent invention has beenl L l shown and described herein, other embodiments distributor chamber one of the valves could be in l5 and many modifications may be obvious to those skilled in thel art without departing from the spirit or scope of the inventionas defined by the claims appended hereto.

I claim: l. A magneto unit including a current disutor arm, a separate chamber for said.v mechanism, a stationary sleeve mounted in. and extending through a wall of said chamber, a drive shaft extending through said sleeve and connected to said distributor arm, and a sealing means for said shaft to prevent the entrance of external air to said chamber between said sleeve and shaft.' said sealing means including a seal ring carried by said sleeve, a seal ring carried by said shaft and rotating therewith, and means to force said rings into sealing contact engagement.

2. A magneto unit for airplane engine ignition systems including a current distributing mechanismhaving a rotatable distributor arm, means providing a chamber for said mechanism, a drive shaft extending into said chamber and connected to said distributor arm, and a sealing means for said shaft to prevent the entrance of external air to said chamber, said sealing means including a flexible diaphragm, a non-rotatable seal ring'and va rotatable seal ring, one of said seal rings being mounted by means of said flexible diaphragm, resilient means on one side of said diaphragm to force said latter seal ring into surface contact engagement wth the other seal ring. said sealing means being so arranged that the said chamber communicates with the side of said diaphragm on which said resilient means is located whereby the pressure of the medun'i within said chamber will supplement said resilient means on increase in altitude in maintaining the contact engagement between saidseal rings.

3. A magneto unit including a coil having a high tension terminal and a current distributing mechanism having a rotatable distributor arm, a chamberl for enclosing said mechanism, a statlonary sleeve extending through a wall of said chamber, bearings carried by said sleeve, a drive shaft extending through said sleeve and journaled in said bearings and connected to rotate said distributor ann, and means to electricallyv connect said high tension terminal to said distributor arm includng said drive shaft, said sleeve and bearngs' being uninsulated from,v said shaft and at the same relative potential as said shaft.

4. A magneto unit including a coil having a high tension terminal and a current distributing mechanism having a distributor rotor of insulating material with a distributor arm, a chamber of insulating material` for enclosing said mechanism, a stationary metal sleeve extending through a wall of said chamber, bearings carried by said .sleeve a metal drive shaft extending through maintain the close mechanical tolerances lnesaid sleeve and provided with a drive gear-of insulating material, means connecting said shaft to said distributor rotor, and means to electrically connect said shaft to said high tension terminal and said distributor arm whereby said sleeve and bearings will be at the same relative potential as said, shaft.

5. A current distributing mechanism having a rotatable distributor arm, means providing a chamber for said mechanism, a drive shaft extending through a Wall of said chamber and spaced therefrom, said drive shaft having its inner end connected to said distributor arm within said chamber, and a sealing means for said shaft adjacent the outer end of said shaft and outside of said chamber to prevent the entrance of external air to said chamber through the space between said shaft and chamber wall.

6. A magneto unit including a coil having a high tension terminal and a. current distributing mechanism having a rotatable distributor arm, a chamber for enclosing said mechanism, a drive shaft extending through a wall of said chamber, said drive shaft having its inner end mechanically and electrically connected to said distributor arm within said chamber and having its outer end electrically connected to said high tension terminal outside of said chamber, and a sealing means for said shaft to prevent the entrance of external air to said chamber.

7. A current distributing mechanism having a rotatable distributor arm, a chamber for said mechanism, a stationary sleeve mounted in and extending through a wall of said chamber, a drive shaft extending through said sleeve and connected to said distributor arm, and a sealing means for said shaft to prevent the entrance of external air to saic chamber between said sleeve and shaft, said sealing means including a seal ring carried by the outer end of said sleeve, a seal ring carried by said shaft and rotating therewith, and means to force said rings into sealing contact engagement.

8. A current distributing mechanism having a rotatable distributor arm, a chamber for said mechanism, a stationary sleeve mounted in and extending through a wall of said chamber, a drive shaft extending through said sleeve, said drive shaft having its inner end connected to said distributor arm within said chamber, a drive gear connected to the outer end of said dive shaft outside of said chamber, and spaced bearings between said sleeve and drive shaft, said bearings being located adjacent the inner and outer ends of said sleeve on opposite sides of said chamber Wall.

9. A current distributing mechanism having a distributor rotor, a chamber for said mechanism, a stationary sleeve mounted in and extending through a wall of said chamber, a drive shaft extending through said sleeve, said drive shaft having its inner end connected to said distributor rotor within said chamber, a drive gear oonnected to the outer end of said drive shaft outside of said chamber, and spaced bearings for mounting said drive shaft in spaced relation to said sleeve, said bearings being located adjacent the inner and outer ends of said sleeve and interposed between said sleeve and distributor rotor and between said sleeve and drive gear.

10. A current distributing mechanism having a rotatable distributor arm, a chamber for said mechanism, a stationary sleeve mounted in and extending through a wall of said chamber, a drive shaft `extending through said sleeve, said drive shaft having its inner end connected to said distributor arm within said chamber, a drive gear connected to the outer end of said drive shaft outside of said chamber, and means to mount said drive shaft to rotate within said sleeve including a bearing housing on said gear and an antifriction bearing interposed between said bearing housing and the outer side of said sleeve..

, 1l. A current distributing mechanism having a distributor rotor including a bearing housing, a stationary sleeve, a drive shaft extending through said sleeve, said drive shaft having one end thereof connected to said bearing housing, and means to mount said drive shaft to rotate within said sleeve including an Aantifriction bearing interposed between said bearing housing and the outer side of said sleeve.

12. A magneto unit including a coil having s high tension terminal and a current distributing mechanism having a distributor rotor including a bearing housing, a stationary sleeve, a drive shaft extending through said sleeve, said drive shaft having end thereof connected to said bearing housing and the other end thereof electrically connected to said high tension terminal, a distributorarm connected to said bearing housing, and means to mount said drive shaft to rotate within said sleeve including an antifriction bearing interposed between said bearing housing and the outer side of said sleeve.

13. A current distributing mechanism having a rotatable distributor arm, a chamber for enclosing said mechanism including a wall constituted of insulating material having a metal sleeve molded therein and extending transversely through said wall, a drive shaft extending through said sleeve, said drive shaft having the inner end thereof connected to said distributor arm within said chamba', and bearings between said shaft and said sleeve.

WILBUR L. CARIBON.

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