US2169597A - Magneto generator - Google Patents

Description

Aug. 15, 1939. w, J SPENGLER 2,169,597

MAGNETO GENERATOR Filed Oct. 24, 1936 4 Sheets-Sheet 1 INVENTOR.

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Aug. 15, 1939. w. J. SPENGLER MAGNETO GENERATOR Filed Oct. 24, 1936 4 Sheets-Sheet 2 INVENTOR.

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w. J. SPENGLER 2,169,597

MAGNETO GENERATOR Filed Oct 24, 1936 4 Sheets-Sheet 3 INVENT OR.

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Aug. 15, 1939. I w J. SPENGLER 2,169,597

MAGNETO GENERATOR Filed Oct. 24, 1936 4 Sheets-Sheet 4 W /m /tag Moss spark ga V2 vl/oitage accoss and 1/otage across condenser INVENTOR. ,wm BY Spy Patented Aug. 15, 1939 PATENT OFFICE MAGNETO GENERATOR Walter J. Spengler, Sidney, N. Y., assignor to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application October 24, 1936, Serial No. 107,461

6 Claims.

The present invention relates to magneto generators and more particularly to high tension magnetos for ignition systems of internal combustion engines.

The ignition requirements for high speed multicylinder engines have become progressively more difficult to satisfactorily meet as the speeds and numbers of cylinders of engines have increased, thus increasing the number of sparks per second required. It has been found that with ordinary commercial equipment the efliciency of the ignition device falls off quite rapidly above a critical speed, and it has been further observed that this loss of efliciency is periodical in character. That is, substantially normal and sub-normal sparks alternate in regular sequence.

On further investigation it has been discovered that under these circumstances there is insufficient time for the energy generated in the secondary winding of the ignition coil to be completely dissipated in the form of a spark before the breaker points in the primary circuit reclose. This undissipated energy produces, at the moment the contacts close, a magneto-motive force in opposition to the one generated by the rotation of the magnet, causing a reduction in the energy generated for the succeeding spark. Since there is thus less energy stored in the secondary winding of the coil in the ensuing cycle, it is quickly dissipated and does not interfere with the following spark, so that the sparks are alternately normal and weak as above noted.-

It is an object of the present invention to provide a high tension magneto which is eflicient and reliable in operation at high speeds.

It is another object to provide such a device which incorporates means for accelerating and intensifying the high tension discharge.

It is a further object to provide such a device which incorporates means for preventing undissipated energy of one cycle of operation from adversely affecting the operation in the following cycle.

It is another object to provide such a device in which energy which is not dissipated in a high tension discharge is used regeneratively to increase the energy of the following discharge.

A still further object is to provide suchv a device in which the regenerative means is incor-, porated in the distributor mechanism.

Further objects and advantages will be apparent from the following description taken in connection with the accom nying drawings in which:

Fig. .l-is a vertical substantially mid-sectional bodying a preferred form of the present invention;

Fig. 4 is a section taken substantially on the 10 line 4-4 of Fig. 3;

- Fig. 5 is a view in perspective of the condenser illustrated in Figs. 3 and 4;

Fig. 6 is an exploded view in perspective showing the arrangement of the plates of the con- 15 denser;

Fig. 7 is an exploded view in perspective and partly broken away of a rotor showing a somewhat diiierent method of incorporating the condenser therein;

Fig. 8 is a vertical substantially mid-sectional view of an assembled rotor of the type illustrated in Fig. 7; and

Figs. 9, 10, 11 and 12 are curves of operation of high tension ignition devices. Fig. 9 illustrates 25 the primary and secondary current flow in a conventional type of magneto rotated somewhat above its rated speed. Fig. 10 shows the same phenomenon when the rotation is still faster. Fig. 11 is a similar record of a magneto embody- 0 ing the present invention, and Fig. 12 illustrates the primary and secondary voltages and the voltage across the spark gap of an ignition system incorporating the present invention.

Referring first to Fig. 1 of the drawings, there 85 is illustrated a magneto comprising a'frame I in which is rotatably mounted a magnetic rotor 2 arranged to be driven from a suitable rotary element of the engine to be ignited. A suitable induction coil 3 is mounted above the rotor in 40 the frame I with its core 4 in a magnetic circuit which includes the rotor 2.

The high tension output of the coil 3 is connected by means of conducting means 5 to the central terminal 6 of a rotor l which is suit- 45 ably mounted in the frame as by means of a bearing 8 and is driven from the magnetic rotor 2 by means of a pinion 9 on the magnetic rotor shaft which meshes with a gear II on the distributor shaft I2. I

According to the present invention, a condenser l3 (Figs. 3, 4 and '5) in the form of a wafer composed of alternately disposed groups of plates H and I5 (Fig. 6) separated by suitable sheet dielectric material I6, is embedded within the body of the rotor I as best illustrated in Figs. 3 and 4. As there shown, the rotor I is formed of molded dielectric material which completely encloses the condenser l3 and has molded therein the central terminal 6 and a radially arranged terminal H, the ends of which terminals project slightly from the face ofthe rotor.

Conducting means here shown as tabs l8 and I9 extending from the condenser plates l4 and I5 respectively, are arranged to protrude from the condenser and connect to the terminals 6 and I1 respectively.

A circular series of terminal members 2! (Fig. 1) are arranged adjacent the path of the rotor terminal H, and are formed to receive the high tension cables not illustrated, which connect with the spark plugs of the engine cylinders.

In Figs. 7 and 8 there is illustrated an embodiment of the invention in which the rotor is molded with a recess 20 in which a condenser 23 is mounted. The recess 20 is preferably undercut as indicated at 20c, and a suitable plastic dielectric material 25 is poured or pressed into the recess so as to enclose the condenser therein, said recess being preferably closed by a suitable cover plate 26 retained by cap screws 21. In this case the radial contact 28 is retained by means of a cap screw 29 in a recess 3| in the periphery of the rotor.

The operation of the present device can best be understood by reference to the performance curves of Figs. 9, 10, 11 and 12, based on records made by a cathode-ray oscillograph.

In Fig. 9 I1 and 12 represent the primary and secondary currents respectively of the ignition coil in a conventional type of installation having no condenser in the high tension output circuit, and operating at high speed. It will be noted that at the point where the breaker points first close, the secondary current is substantially all dissipated, and the primary current builds up in the normal manner. However, when the points reclose, there is still a considerable flow of secondary current, and due to the magneto-motive force thereof, a primary current is immediately generated in the same direction as the previous primary current. The impressed flux from the rotor consequently has to first overcome the reverse flow of current in the primary circuit before it can build up the primary current in the proper direction, so that the energy storage is less than normal. The secondary discharge derived therefrom is consequently sub-normal, is therefore soon dissipated and does not interfere with the next cycle of operation. Under these circumstances, the sparks are therefore alternately normal and sub-normal as above stated.

Fig. 10 illustrates the operation of the same installation when it is rotated at still higher speed. As the speed is increased from above that recorded by Fig. 9, a point is reached at which the inefiicient spark begins to interfere with the ensuing good spark. This reduction of .the effectiveness of the good sparks reduces their interference with the ensuing poor sparks, so that a condition of balance is soon reached in which all the sparks are substantially equally inefiicient. This is the condition illustrated in Fig. 10 where it will be noted that in each instance when the contacts close, the primary current 11 flows initially in a direction reverse to that desired, with a consequent loss in efiiciency due to the interfering effect of the previous secondary current flow Ia.

Referring now to Fig. 11, performance curves are here shown which illustrate the operation of the present invention. As here shown, I: is the secondary current and Is is the primary current. It will be notedthat the insertion of the condenser in the high tension lead causes the spark discharge to take place in two stages a and b, the second stage 12 being of reverse polarity. Under these conditions, the undissipated energy in the secondary circuit at the time the breaker points close produces a magneto-motive force in the primary circuit of the proper polarity to aid the magneto-motive force produced by rotation of the rotor in storage of energy for the following spark. Thus the performance of the magneto at high speeds is substantially improved by means of the regenerative effect secured by the insertion of the condenser in the secondary circuit.

This phenomena may further be explained by reference to Fig. 12 in which curve V1 shows the voltage across the spark gap, curve V2 shows the voltage across the secondary terminals of the coil, and curve V3 shows the voltage across the condenser. It will be seen that the voltage V2 across the coil rises very rapidly after opening of the breaker points until point A is reached. At this point the spark gap breaks down so that the current starts to flow in the secondary circuit, charging the condenser therein. The potential V3 across the condenser increases as current continues to flow across the gap. The voltage Va across the coil reaches its maximum value and starts to decline. When the point B' is reached, the voltage across the coil and the voltage across the condenser are equal so that there is no voltage drop across the gap, and the secondary current falls to zero. The voltage V2 across the coil continues to fall, while the voltage V: across the condenser remains constant due to the energy trapped in it until point C is reached. At this point the voltage Vi across the gap, which is of course the difference between the voltage across the coil and the voltage across the condenser, is sufiicient to break down the gap again. Since the voltage across the gap is now of reverse polarity, the current in the secondary circuit is also reversed and the condenser discharges. If the breaker points close before the condenser has completed this discharge, the discharge current flowing through the secondary of the coil induces a current in the primary in the same direction as that produced by rotation of the magnetic rotor. Thus the degenerative effect in the conventional magneto, caused by the breaker closing before the secondary energy is completely dissipated, is changed to a regenerative effect when the series condenser is incorporated in the high tension secondary circuit.

It will be understood that the capacity of the series condenser must be great enough to store up suflicient energy for a satisfactory ignition spark, or, in other .words, at least a major fraction of the energy. of the secondary discharge, since the energy which produces the spark must all be stored in the condenser. On the other hand, the condenser must be of small enough capacity so that it will be charged to a voltage substantially above the break-down voltage of the spark gap, since otherwise there would be no reverse discharge from the condenser and therefore no regenerative effect. It has been found by investigation and experimentation that with commercial forms oftmagnetos the capacity of this condenser is preferably in the range between about 1200 micromicrofarads and 2200 75 2,100,597 micromicrofarads or specifically in the neighbor-v hood of 1700 micromicrofarads.

While certain preferred structure has been shown and described in detail, it will be under-.

stood that various modifications can be made in the design and proportions of the parts without departing from the spirit of the invention as defined in he appended claims.

What is claimed is:

1. In a high tension ignition system for multicylinder engines a source of high tension current, means for distributing such current to the ignition devices of the engine cylinders in sequence including a rotor in the form of a disc having radially spaced electrical terminals, and an electrostatic condenser located within the disc and connecting said terminals.

2. In a high tension ignition system for multicylinder engines a source of high tension current, means for distributing such current to the ignition devices of the engine cylinders in sequence including a rotor in the form of a disc of dielectric material, radially spaced electrical terminals molded therein, and an electrostatic condenser molded within the disc and connecting said terminals.

3. In a high tension ignition system for multicylinder engines a source of high tension current, means for distributing such current to the ignition devices of the engine cylinders in sequence including a rotor in the form of a substantially circular dielectric disc, an axially arranged terminal mounted therein, means for connecting said terminal to the source of high tension current, a radially arranged terminal in said disc, means for connecting said radial terminal to the ignition devices of the engine cylinders in sequence, and an electrical condenser enclosed within said disc, the opposite plates thereof being connected to said terminals respectively.

4. In a high tension ignition system for multicylinder engines a source of high tension current, means for distributing such current to the ignition devices of the engine cylinders in sequence including a rotor in the form of a substantially circular disc molded from plastic dielectric material, an axially arranged terminal mounted therein, means for connecting said terminal to the source of high tension current, a radially arranged terminal in said disc, means for connecting said radial terminal to the ignition devices of the engine cylinders in sequence, and an electrical condenser completely embedded within said disc, the opposite plates thereof being connected to said terminals respectively.

5. In a high tension ignition system for multicylinder engines a source of high tension current, means for distributing such current to the ignition devices of the engine cylinders in sequence including a rotor in the form of a substantially circular disc molded from plastic dielectric material, an axially arranged terminal mounted therein, means for connecting said terminal to the source of high tension current, a radially arranged terminal in said disc, means for connecting said radial terminal to the ignition devices of the engine cylinders in sequence, an electrical condenser completely embedded within said disc. and conductors molded in said disc connecting the opposite plates of the condenser to said terminals respectively.

6. A rotor for a high tension electrical distribg ed in said disc and projecting therefrom.

WALTER J. SPENGLERQ

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