US2546108A - Electrical ignition device - Google Patents

Description

March 20, 1951 P. T. Nuvis 2,546,103

ELECTRICAL IGNITION DEVICE Filed June 15, 1946 5 Sheets-Sheet 1 INVENTOR. P/i UL. T. N/MS By My flTTOR NE Y5 March 20, 1951 P. T. NIMS 2,546,103

ELECTRICAL IGNITION DEVICE Filed June 15, 1946 5 Sheets-Sheet 2 INVENTOR. PAUL 7w IV/MS l a/mm A a/m flTTORNEX March 20, 1951 P. T. NIMS 2,546,108

ELECTRICAL IGNITION DEVICE Filed June 15, 1946 3 Sheets-Sheet 5 Wflfllb); 136 is; 138 a 2 8 5 LNVENTOR. PAUL 7." 'N/M.

WWW 14 TTOR/VE 75 Patented Mar. 20, 1951 ELECTRICAL IGNITION DEVICE Paul T. Nims, Detroit, Mich, assignor to Chrysler Corporation, Highland Park, Mich, a corporation of Delaware Application June 15, 1946, Serial No. 676,891

Claims. (Cl. 171-209) This invention relates to electrical ignition devices, for instance, magnetos, and more partic ularly to a ventilation system for such devices providing forced air ventilation for inhibiting corrosion of metal parts and to means for inhibiting flash-over grounding of normally high potential currents in such devices.

Magnetos, as is well known, are employed, for example, for generating the current for the electric ignition in internal combustion engines. Hence, for the purpose of illustrating my invention, I shall make reference to a magneto used for aircraft engines.

v One of the principal complaints encounter-ed in operation of magnetos, especially those for aircraft application, has been the deleterious corrosion of metal parts and breakdown of lubricating greases. I have found these to be caused by the presence of acid or oxidizing fumes generated by electrical discharges in the air of themagneto. These discharges are produced by the high potential current flashes or sparks passing between the distributor rotor contact and the successive distributor contacts controlling current now to the spark plugs of the engine cylinders, during rotation of the rotor, which in aircraft application many, for instance, make 10,000 or more contacts per minute. The sparking apparently breaks down the surrounding air and generates nitrous oxide, nitric oxide and ozone fumes in substantial amounts. The presence of moisture facilitates the formation of nitric acid with disastrous results.

The fuming action is also contributed to by sparking across the low tension make and break contacts and the corrosive results are enhanced by high temperatures in the magneto, and compact construction where ventilation is difiicult.

Another problem is the unintentional grounding of a normally high potential current in the magneto made possible by continuous tracking caused by flash-over of excessively high potential current.

By flash-over I mean the jumping of a high potential current from a hot contact to grounded metal over intervening insulation. By high potential currents I mean currents at such a voltage as will cause flash-over (also called sparking-over) in air. By tracking I mean the formation of a layer of carbon by flash-over which provides a conducting part for current. By excessively high potentials I mean those greater than the insulation strength of the air or gas between any two electrodes.

The'aforesaid conditions are commonly encountered, for instance, in aircraft engine magnetos, especially at high altitudes and when the spark plugs are open circuited or insulated by a film of oil. In these circumstances the normal potentials of 5,000 volts build up to 25,000 volts or more and the current seeks a ground. The thinness of the air at high altitudes reduces its elfectiveness as an insulation and the current grounds by flash-over from the hot terminal of the distributor to some grounded metal part with which it normally ha no electrical connection. The sparking burns the surface of the insulation to form a continuous carbonaceous layer which materially shortens the insulation gap to the grounded metal. Consequently thereafter at lower altitudes, for instance, sea level where the operating potential is about 12,000 volts, the insulation is insufficient to prevent continuous fiash-over to the grounded metal and grounding of the ignition system results.

I have discovered that the foregoing corrosive diiiiculties may be minimized by providing for the elimination of the fume-laden air or gas from Within the magneto housing, for example, by creating a pressure differential in the air or gas within the housing so as to effect a flow thereof in a direction to exhaust the fumes. In this connection I have found it advantageous to give the distributor mechanism the added characteristic of a centrifugal blower and to separate the current generating mechanism from the distributor mechanism so as to as far as possible confine the fume production to the distributor chamber so that the direction of air flow may be made from the current generating chamber to the distributing chamber, to the outlet to avoid recirculation of the fumes and their introduction into the current generating chamber. Thus I .so construct the distributor rotor to have one or more arms to act centrifugally on the air or gas in the housing so as to direct it to the outlet port and by the partial vacuum created adjacent the transfer port cause a flow of air from the generator to the distributor chambers and from the latter out of the housing. In this connection the distributor plate is by preference constructed to form generator and distributor chambers in the housing and is provided with ports adjacent the rotor axis to permit transfer of air or gas between the generator and distributor chambers. In addition an air inlet is provided to the generator chamber and an air outlet from the distributor chamber, the latter being at a greater radial distance from the rotor axis than the transfer parts and by preference being connected 3 with the distributor chamber through the distributor plate.

I have further discovered that the danger of grounding of the high potential currents aforesaid may in most cases be entirely eliminated and in others greatly lessened by an arrangement of structure which compels the current to jump an air gap formed in the insulation body surrounding the hot contact responsible for the condition, and which gap lies in the path the current would take in its flash-over from the hot contact to the grounded metal. Preferably such gap or gaps will be formed by one or more reentrant grooves, or furrows in the insulation material and crossing the current flash-over path. These gaps prevent a continuous carbon track from being formed by fiash-over burning of the surface insulation between the hot contact and the grounded metal or over the entire insulation surface between these two. Although the surfaces adjacent the gaps may be burnt the air gaps will be sufficient to prevent the normal current potentials from jumping the same.

Inasmuch as the actual operating conditions and actual structures will vary, it is difficult to give gap dimensions with any exactitude. However, I have found that the air gap should be sufiicient to prevent flash-over by the normal operating potentials between the adjacent ends of the carbon track formed by flash-over of the excessively high potential currents. In general a gap between adjacent insulation lands having a depth at least equal to its width is preferred. Moreover, one or more gaps /8" wide depending on the normal potentials to be met will be found satisfactory. In this connection a. plurality of air gaps have a somewhat cumulative effectthough not directly as the number of gaps.

Accordingly, it is the general object of my invention to provide an improved electrical ignition device, for instance, a magneto structure in which the dangers of corrosion from acid and/or oxidizing fumes and from flash-over grounding at normal operating potentials are inhibited or substantially eliminated.

Another object is to provide a forced; air ventilation system for magnetos. A specific object is to provide in a magneto a, distributor construction simulating a centrifugal blower whereby to remove corrosive fumes from the interior of the magneto.

A further object is to provide a resilient conduit between an air exhaust port and a distributor plate exhaust port connecting with the distributor chamber. that seats and seals against the distributor plate when the distributor, cap is assembled to the magneto housing.

Another object is to provide a structure for preventing continuous trackage due to excessively high potential currents under flash-over conditions.

An additional object is to provide one or more recesses or grooves formed by a plurality of lands, or projections, or offsets in the surface of the insulation material between a hot high tension contact and the nearest grounded metal to prevent continuous tracking by flash-over of the current to said ground by excessively high potential currents whereby to prevent subsequent grounding at normal operating potentials.

Other objects and advantages of my inven ion will become more apparent from the following description taken in connection with. the accompanying drawing wherein:

' Fig. 1 is an end elevation of the mounting end d. of the magneto showing the air exhaust ports and flame arresters therein;

Fig. 2 is an elevational cross-sectional development taken along the line 2-2 of Fig. 1;

Fig. 3 is an end elevational view partly in section taken at 33 of Fig. 2 showing the interior of the distributor chamber; and

Figs. 4, 5, 6, and '7 are several anti-grounding arrangements, shown somewhat schematically.

Referring to the drawings wherein similar numerals refer to similar parts throughout the several views, the magneto housing is generally represented by the numeral Ill and comprises a central shell. [2 carrying the current generator field structure generally designated by the numeral M; an annular casing it telescoping with the shell 12 at flange and carrying the distributor mechanism generally identified by the numeral 20; a terminal conduit 22 closing the outer open end of the distributor casing l6; and a bearing bracket 24 secured b bolts 26 to the shell l2, closing the outer end of the shell 12, this member 24 also serving as a mounting bracket for the entire unit.

Fitted into the casing member it and secured thereto by studs 2! is an annular moulded, distributor cap 38 of electrical insulation material. The cap 35] comprises a cylindrical rim portion 32 and a hub-like portion 34, the rims being shouldered at 3,6. to receive a distributor plate 38 which divides the magneto into two chambers, a current generator chamber 40 and a distributor chamber 42.

A two-arm distributor rotor 44 preferably of a shape used in centrifugal blowers is fixed to a shaft 46 supported for rotation in the ball bearings 6,8 and as respectively carried in the. plate 38 and hub 3.4.

The generator field structure includes the fixed pole shoes 52 (see Fig. 2) secured to the shell l2... coil cores 54 and two coil assemb ies 56 each having an inner primary winding 58 and an outer secondary winding 60.

A magnet, rotor generally designated by the numeral 62 is fixed to a. shaft 64 rotatably carried in a ball bearing 66 of the bracket 24 and a ball bearing 68 secured in a bearing housing Ill carried by the inner portion 12. of the pole piece. The magnet rotor and distributor rotor shafts are co-axial and are drivingly connected by a coupling. member l4 splined to each of the shafts and supported in a ball bearing 16 in the: bearing housing, ill. The coupling M carries the make and break cam 18. for operating the make and break contact arms of the make and breakmechanism 1.9. supported on a, grounded metallic. plate 80. The outboard end of the shaft 64 is splincd to receive. a driving member 82 for driving the rotor for instance at half engine speed.

Arranged concentric with the distributor rotor axis on the, distributor chamber side of the dis,- tributor plate as shown in Fig. 3, are two groups of spaced contacts 84. each group being secured to a segmental circular conductor bar 86 having abent tab 83 (see Fig. 2) which extends through the distributor plate into contact with a button type spring based contact 90 which electrically connects the secondary winding in circuit with these contacts 84.

A second group of contacts 92 arranged concentric with the first mentioned group but at a greater radial distance are mounted in the distributor cap 3'9. Each of these contacts is connected by a suitable wire conductor to the spark plug on which it is to supply a high potential current. Current is brought to these contacts through the medium of contactors 94 carried by the distributor rotor 44, these contactors having a projection 96 which during rotation of the rotor successively comes within electrical connection with, but not touching, the individual contacts 84 and having a second projection 98 similarly successively obtaining electrical relation with the individual contacts 92. Hence, when the projection 98 is over a contact 84 the projection 98 is over a contact 92 and high tension current may flow to the selected spark plug through the above named elements, such current jumping an air gap between the rotor and distributor contacts.

During rotation of the distributor rotor many contacts are made and broken with an accompanying flash or spark as the high potential current jumps any intervening air gap between contacts. These sparks cause a breakdown in the surrounding atmosphere with the production of the corrosive fumes described above which if permitted to remain or circulate in the current generator or distributor chambers will attack all metal parts or grease within its reach.

To eliminate these fumes, I provide, for example, in the distributor plate 38 a pair of openings I00, I02 respectively, each located at a different radial distance from the axis of the rotor 44 but not necessarily in radial a ignment with each other. The inner opening I9! serves to connect the distributor chamber with the current generator chamber which latter has one or more, preferably a plurality of a r ports I84, each having mounted therein a flame proof air breather I96 adapted to admit air into the current generator chamber. The second or outer opening I02 in the distributor plate 38 connects the distributor chamber to the outside atmosphere through a tubular resilient conduit I I38 made, for example, of resilient but form retaining natural or synthetic plastic, for example, rubber or vinyl resin which member in turn connects with an air escape bore or conduit opening III! in the shell I2 (see Fig. 2), the latter having fitted into its terminus a flame proof air breather II2 which permits the expulsion of gas from Within the distributor chamber.

As shown, the tubular member IE8 is seated in a shouldered portion II4 of the air escape bore III) to which it is suitably held as, for instance, by a suitable cement. The other end of the member I08 has a portion of greater section forming a flange I I6 which rings the opening I02 and seats and seals in pressure contact with the current generator chamber side H8 of the distributor plate. This arrangement makes it feasible to remove the distributor assembly for adjustment of the make and break contacts in the generator chamber or otherwise gain access into the latter chamber without necesitatina a permanent connection between the conduit I 08 and the distributor plate.

It will be understood that although I have shown two openings I and two openin s I I12 with their associated connections, a single one of each and more than two may be employed.

It will be observed that the distributor rotor has oppositely outwardly tapered arms I20. These arms have edge faces I22 which on rotation of the rotor are adapted to act on and outwardly displace air or gases within the distributor chamber, it being noted in this connection that the thickness of the arms is by preference a substantial proportion of the axial length of this chamber.

During rotation, the distributor mechanism arj ranged as above acts as a centrifugal blower, the air and gases in the distributor chamber being displaced outwardly by centrifugal action and passing through the openings H12 in the distributor plate through the conduit I88, through the breather I i2 and outside of the magneto. As these gases are displaced, a suction action occurs in the region of the inner openings Ibo of the distributor plate and air at a lower pressure is drawn into the distributor chamber from the current generator chamber which in" turn draws fresh air in from the breathers I66 since the air pressure at this point is also less. Thus the corrosive gases generated in the distributor chamber do not find their way into the generator chamber but are expelled from the distributor chamber to the outside and consequently, the magneto parts and grease in the current generator chamber are protected from attack. In addition, the positive movement of gases and air effected by the present invention aids in cooling the magneto.

Referring now to Figs. 2 and 3, it will be noted that the outer edge of the openings I98 of the distributor plate on the distributor chamber side is formed with a pair of spaced, concentric, raised narrow insulation ribs or beads I24 preferably rounded or peaked. These ribs by preference are at least co-extensive with the circumferential length of the openings, the instant embodiment disclosing a pair of concentric annular ribs. Between the ribs is a relatively deep valley I25 preferably of a depth at least equal to its width.

The purpose of this undulated structure is to prevent flash-over of the normal high voltage current from the contacts 84 or conductor bar 86 to grounded metal parts in the current generator or distributor chamber, for instance, the metal plate 38 and th primary make and break contacts secured to the plate 88 with which the high potential contacts are not electrically connected. As described above, excessively high potential currents build up at times when the ignition circuit to the spark plugs may be blocked, and tend to seek another ground such as the ground through the make and break mechanism 19 and, if successful, spark-over to such contact burning the intervening insulation surface to form a layer of carbon. The presence of this carbon provides a conducting path to ground for lower potential currents. Any burning of the insulation material adjacent contacts 84 tends to reduce the distance to the ground. By providing one or more recesses or valleys 25 I prevent a continuous conductor surface from being formed by the carbon deposit since the discharging current will not burn the insulation surface in the bottom of the valleys.

As shown in Fig. 2 the current generator side of the distributor plate has a similar arrangement of concentric ribs adjacent the button contact 98 to serve as a protection against grounding of the high tension current by discharge from this point or the contact 88.

It will be understood that the new structure is not limited to a single valley or recess or groove, but may include as many as desired.

Figures 4 to '7 show schematically modified forms of insulation structure for inhibiting flashover at normal potential. Thus in all figures, 84 is the hot contact and 8B the grounded metal comparable to those of Fig. 2. The air gap I28 in Fig. 4 is provided by the adjacent lands I30, I32 formed by projection I33. The air gap I34 in Fig. 5 is provided by the adjacent lands I36, I38.

7 In Fig.6 ther are two air gaps; Me, M2- respectively provided by the raised rib M3 which: with the adjacent insulation forms adjacent lands i l i, I46, and I48, use. In Fig. '7 two spaced raised ribs I51, I52 provide three air gaps i 1, E56,, I58 with the adjacent surface.

It is. to be. observed that in Figs. 2, i, 5, and. 6 there is an air gap between the insulation and. the grounded metal. This air gap is not intentional but is present as an incident to the general arrangement of parts. It: adds to the protective value of. the arrangement but in most instances is not in itself sufficient. Inv practice it is seldom that the distance between the hot contact and nearest grounded metal exceeds one inch and any air gap between insulation and grounded metal is small. The present invention contemplates that the requisite air gap shall be provided in. the insulation body and any incidental air gap is disregarded so that protection is aiiorded whether or not the grounded metal has contact with the insulation body.

While the particular structure herein described is well adapted for carrying out the objects of th present invention, it will be understood that various modifications, changes, and substitutionsmay be made without departing from the. spirit thereof. For example, the invention has application to automotive ignition systems where the bearings, rotor mechanism, and make and break contacts of the ignition coil primary current are in the samehousing as the distributor mechanism and consequently the corrosive fume problem described above exists. By applying the teachings of the. pr' sent invention, the operating parts of the mechanism may be protected. Hence, the expressions, generator chamber and generator mechanism are used in a generic sense and are not intended to be limited to structures actually having current generator mechanism but also to include arrangements employing a battery or other power source for current but having oper ating mechanism, for instance, make and break mechanism housed with the distributor mechanism and that will be attached by corrosive fumes generated by the latter.

The present invention is therefore to be construedas including all such modifications, changes and substitutions as may come within the scope of the following claims.

I claim:

1. In an electrical ignition device including current generating mechanism and high tension current distributing mechanism; a housing enclosing said mechanisms, a partition dividing said housing into a chamber containing said generating mechanism and a second chamber containing said distributing mechanism, a fresh air inlet port connecting said generating chambe with the exterior of said housing, a contaminated air out let port connecting said distributing mechanism chamber with the exterior of said housing air propeller means within said distributor chamber for centrifugally acting upon the contaminated .air therein whereby to expel said contaminated air through said outlet port and facilitate the. flow of replacing air from said generator chamber into distributor chamber and of fresh air into said generator chamber and an ai transfer port in said partition at a lesser radial distance from the axis of rotation of said propeller than said outlet port.

2. In. an electrical ignition device includin current generator mechanism and high tension cur- :rent distributor mechanism; a housing, enclosing said: mechanisms, a: distributor contact plate partitioningsaid housing into a first chamber containing said generator mechanism and a secondchamber containing said distributor mechanism a distributor rotor in said second chamber drivopening into said first and second chambers, a-

second recess in said plate further removed from. said axis than said. first recess, an air outlet port 7 in said housing and a conduit connecting said outlet port with said second recess.

3. Inch electrical ignition device including current generator mechanism and high tension cur rent distributor mechanism; a housing enclosing;

said mechanisms, a distributor contact plate parti-tioni'ng said housing into a first chamber containing said generator mechanism and a second chamber containing said; distributor mechanism, a distributo rotor in said second chamber drivingly connected to said generator mechanism, said rotor. having a radially extending arm adapted to effect centrifuged displacement of air in said second chamber, an air inlet port in said housing opening into said first chamber, a first recess in said plate adjacent the axis of said rotor and opening into said first and second chambers, a second recess in said plate further removed from said axis than said first recess, an air outlet port in said housing and a flexible conduit connecting said outlet port with said second recess.

4'. In an electrical ignition device including current generator mechanism and high tension current distributor mechanism; a. housing enclosing said mechanism, a distributor contact plate partitioning said housing into a first chamber con taining said generator. mechanism and a second chamber containing said distributor mechanism, a distributor rotor in said second chambe drivingly connected to said. generator mechanism, said rotor having a radially extending arm adapted to efiect centrifugal displacement or. air in said second chamber, an air inlet port in said housing opening into said first chamber, a first recess in said plate adjacent the axis of said rotor and opening into said first and second chambers, a second recessin said plate further removed from said axis than said first recess, an air outlet port in said housing and a flexible conduit connecting said outlet port with said second recess, said conduit having a portion secured in said outlet port so as to substantially seal said conduit from air connection with said first chamber and said con duit having a second portion seating around the said second recess and in sealing relation with said distributor plate so as to prevent flow of air between said first and second chambers through said second recess but permit discharge thereof from said second chamber.

5. In an electrical ignition device havinga high tension current distributor rotor; a housing for said device; means partitioning said housing into .a chamber enclosing said distributor mechanism and a second chamber containing other ignition operating mechanism, said partitioning means providing a wall at one side of rotor mounting the same for rotation; a fresh air inlet port connecting said second chamber with the exterior of said housing; a pair of other air ports in said Wall, one of said ports interconnecting said chambers adjacent the axis of rotation of said rotor,

the other port being further removed from said axis and connecting said distributor chamber with the exterior of said housing; and means associated with said current distributor chamber and operable on the air therein for eifecting expulsion of contaminated air from within said distributor chamber through said one port and facilitating admission of fresh air into said second chamber.

6. In an electrical ignition device including circuit breaker mechanism and high tension current distributing mechanism; a housing enclosing said mechanisms, means partitioning said housing to provide separate chambers for said mechanisms, an air inlet port in said housing opening into the circuit breaker chamber, an air transfer port in said partitioning means connecting the circuit breaker and distributor mechanism chambers, an air discharge outlet directly connecting said distributor mechanism chamber with the exterior of said housing and a rotatable air impeller in said distributing mechanism chamber, said discharge outlet being at a greater radial distance from the axis of rotation of said impeller than said transfer port.

7. In an electrical ignition device including circuit breaker mechanism and high tension current distributing mechanism, a housing enclosing said mechanisms, means partitioning said housing to provide separate chambers for said mechanisms, an air inlet port in said housing opening into the circuit breaker chamber, an air transfer port in said partitioning means connecting the circuit breaker and distributing mechanism chambers, an air discharge outlet directly connecting said distributing mechanism chamber with the exterior of said housing, an air impeller in said distributing mechanism chamber, and insulating means at said air transfer port and air discharge outlet for inhibiting fiashover and grounding of high potential currents past said transfer port and discharge outlet.

8. An electrical ignition device as claimed in claim 7 wherein the insulating means at said discharge outlet comprises a long insulating conduit.

9. In an electrical ignition device including high tension current distributing mechanism; a housing providing a chamber enclosing said distributing mechanism, said chamber having walls at the opposite ends thereof, one of said walls mounting a high tension cable structure, the opposite end wall mounting a rotatable air impeller, said impeller being positioned intermediate said opposite walls, a pair of openings in said housing at one side of said impeller and at the end of said chamber oppositie said cable structure, one of said openings being located adjacent the axis of rotation of said impeller and constituting an air inlet for said chamber, the second opening of said pair of openings being located adjacent the outer limits of said chamber relative to said axis of rotation and connecting with the exterior of said housing to provide a contaminated air outlet for said chamber.

10. In an electrical ignition device including circuit breaker mechanism and high tension current distributing mechanism, a housing enclosing said mechanisms, means partitioning said housing to provide separate chambers for said mechanisms, an air inlet port in said housing opening into the circuit breaker chamber, an air transfer port in said partitioning means connecting the circuit breaker and distributor mechanism chambers, an air discharge outlet directly connecting said distributor mechanism chamber with the exterior of said housing, an air impeller in said distributing mechanism chamber, and ribbed insulating means adjacent said air transfer port for inhibiting flashover and grounding of high potential currents past said port.

PAUL T. NIMS.

REFERENCES CETED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,837, 31 Murray Dec. 22, 1931 1,921,427 Nowosielski Aug. 8, 1933 2,285,107 Bohll June 2, 1942 2,286,233 Scott June 16, 1942 2,808,973 Crocker Jan, 19, 1943 2,377,621 Frei June 5, 1945 2,422,150 Upton June 10, 1947 FOREIGN PATENTS Number Country Date 116,592 Australia Mar. 4, 1943 235,274 Great Britain June 5, 1925

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