US2292809A - Induction apparatus - Google Patents

Description

Aug. 11, 1942. w c 2,292,809

INDUCTION APPARATUS Filed'oct. 31, 1940 Inventor: Douglas? W lch,

His Attorney.

Patented Aug. 11, 1942 UNITED STATES PATENT OFFICE mnUc'rroN APPARATUS Douglas F. Welch, Rugby, England, assignor to General Electric Company,

New York a corporation of Application October 31, 1940, Serial No. 363,765

. In Great Britain February 28, 1940 4 Claims.

My invention relates to induction apparatus having particular application to electric ignition systems for internal combustion engines.

An object of my invention is to provide induc- .tion apparatus such that a maximum voltage breakdown of the spark plug gap.

My invention will be more fully set forth in the following description referring to the accompanying drawing, and the features of novelty which characterize my invention will be pointed out in the claims annexed to and forming a part of this specification.

In the drawing the single figure diagrammatically illustrates a magneto for electric ignition systems which is provided with an embodiment of my invention.

In the application of induction apparatus, such as magnetos or induction coils, to electric ignitiou apparatus for internal combustion engines, it is desirable to obtain the largest voltage across the high voltage terminals for a minimum current which is interrupted by the breaker in the primary winding circuit. I have found that this result will obtain when the coupling coefficient between, the primary and secondary windings is of a value of substantially 0.8, or more particularly between 0.75 and 0.85. With a coupling coeflicient having such a value, the peak of the resultant secondary voltage wave occurs somewhat earlier than the peak of the low frequency component.

The coupling coeffici sion V L1XL2 where M is the mutual inductance and L1 and Lo inductances oi the primary and secondary nt is given by the expreswindings respectively.

Referring to the drawing, I have illustrated a conventional circuit having a magneto which is provided to obtain electric ignition for an internal combustion engine. This ignition apparatus of the internal combustion engine.

numeral l0 having a primary winding H and a secondary winding l2. In order to alternate the flux linking the coils a core i3 is provided with an inductor M which rotates in synchronism,

with the rotation of the crank shaft or cam shaft In order to periodically short-circuit the primary winding,

it is connected through the cables l5 and I6 across a breaker having contacts l1 and I8 and an actuating arrangement for the movable contact arm ll such as a cam l9 which is also operated in synchronism with the movement of the crank shaft or the cam shaft of the internal combustion engine. The breaker is also shunted with the conventional condenser 20 and 'one side of the breaker is grounded. One side of the secondary winding I2 is connected to a distributor 2| which will in turn distribute the electric ignition impulse to the spark plugs in the cylinders of the internal combustion engine in proper timed relation. One spark plug is indicated by the numeral 22. One terminal of the spark plug is of course grounded and the secondary winding I2 is connected to one side of the primary winding ll' through the cable 23 so as to form a complete circuit.

If all the flux produced by the primary ing were to link the secondary winding, the coupling coeflicient is equal to one. However, since all the flux of the primary winding does not link the secondary winding the coupling coefficient is of a value less than one. I have found that substantially the largest voltage will appear across the secondary terminals for a given or' predetermined interrupted primary current when the coupling coefllcient between the primary and secondary windings is in the neighborhood of .80, or between .75 and .85. The coupling oothe form of a part turn, a whole turn or even includes a magneto indicated generally by the eflicientcan be so made, in any desired manner, such as by placing between the primary wind- .ing II and the secondary winding l2 a magnetic shunt 24. This magnetic shunt comprises a sheet of magnetic material, such as iron, which is between-the primary and secondary windings and concentric therewith. This shunt may take several insulated turns of a strip of magnetic material of suitable thickness. This thickness together with the width of the shunt determines the extent to which the coupling coefllcient is affected. It is, therefore, possible for the width of the shuntto be equal to, greater than, or less than the length of the coil former, depending upon the thickness and the number 0! turns of the material used. It is also possible for the windshunt to take the form of one or more layers or part layers, woimd with wire having magnetic properties. The shunt could then, if desired,

form a portion of one of the windings. The reduction of the coupling coeflicient may also be efl'ected by including a suitable inductance in series with the primary or secondary windings, or both. The transformer may also be an auto transformer.

In view of the foregoing it will be seen that I have provided an arrangement for obtainingthe largest voltage across the secondary terminals of an induction apparatus for a given primary current. My invention, although not limited thereto, is particularly suitable for an electric ignition apparatus such as a magneto or an induction coil. Thus I provide that the coupling coeflicient between the windings is less than one, or in the neighborhood of 0.80, This desired coupling coefficient may be obtained in any suitable manner and in addition to obtaining the desired secondary voltage wave form, this particular coupling coefficient also reduces the duration of the secondary current between the desired sparks.

Although I have shown and described particular embodiments of my invention,--I 'do not desire to be limited to the particular embodiments described, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention."

What I claim as new and desire to secure by Letters Patent of the- United States:

1. An ignition circuit for producing ignition for an internal combustion engine having an induction apparatus including primary and secondary windings, a breaker connected with said primary winding, and means for providing a coupling coeflicient between said primary and said secondary windings having a value between .75 and .85 so that a substantially maximum voltage is obtained across said secondary winding for a predetermined current interruption by said primary winding breaker.

2. An ignition circuit for producing ignition for an internal combustion engine having an induction apparatus including primary and secondary windings, a breaker connected with said primary winding, and means for providing a coupling coeflicient between said primary and second windings having a value in the neighborhood of .80 so that a substantially maximum voltage is obtained across said secondary winding for a predetermined current interruption by said primary winding breaker.

3. An ignition circuit for producing ignition for an internal combustion engine having an induction apparatus including primary and secondary windings, a breaker connected with said primary winding, and a magnetizable material between said windings and of such dimension in comparison with said windings that the coupling coefficient therebetween will have a value of in theneighborhood of .80 so that a substantially maximum voltage is obtained across said secondary winding for a predetermined current interruption by said primarywinding breaker.

4. A magneto including primary and secondary windings,'means for interrupting said primary winding circuit, and means including a magnetizable material between said primary and secondary windings for providing a coupling coeflicient of said primary and secondary windings of substantially .8. I

DOUGLAS F. WELCH.

Images