US2469133A - Magnetoelectric machine - Google Patents

Description

y 1949- 1 H. SCOTT 2,469,133

MAGNETO ELECTRIC MACHINE Filed NOV. 1, 1945 23 G 22 o 0 if I Z a 4 INVENTOR:

Z759. 2 5. [Aw 17 A. 60077" Patented May 3, I949 MAGNETOELECTRIC MACHINE Lloyd B. Scott, Garden City, N. Y., asslgnor, by mesne assignments, to Jack & Heintz Precision Industries, Inc., Cleveland, Ohio, a corporation of Delaware Application November 1, 1945, Serial No. 636,122

7 Claims. (Cl. 171-209) I This invention relates to electric generators and has particular reference to reversing flux type generators such as magnetos, although the invention is is not limited to that use.

It is well known that in electric generators in which the voltage changes alternately, unwanted impulses occur that may cause improper operation of apparatus energized or otherwise actuated by the generator output. In low tension generators, these unwantedimpulses, although undesirable and therefore to be minimized or eliminated if possible, usually do not materially affect the operation of appurtenant apparatus, but in higher tension generators, the sudden unwanted increase in voltage or voltage increase at the wrong time may cause such diiliculties. For example, in engine ignition magnetos, such unwanted or untimely voltage increases frequently result in the generation of an undesired spark across the spark plug gap irrespective of the operation of the breaker mechanism, thus causing improper operation of the engine, and, in the case of a single cylinder, two-cycle engine, such sparking occurs during the intake stroke and pre-ignition results. The phenomenon is particularly pronounced when the magneto is driven at relatively high speed, when the resulting rapid changes of flux through the magnetic coil cause the regular generation of an untimely spark in the secondary winding regardless of the operation of the breaker mechanism. Various expedients have been adopted to correct this condition, commonly known as maverick sparkling, such as by distorting the pole shoes and the like, and, whereas such expedients reduce maverick sparking they od not eliminate it, and usually result in increased cost of manufacture and complicated structures.

In accordance with the present invention, an electric generator of the reversing flux type is provided in which the generation of unwanted or untimely voltage is minimized or eliminated, by modifying the wave form or amplitude of the voltage generated in the magnetic circuit so that the desired peak voltage only occurs at the proper point or time.

The invention comprises introducing into the magnetic circuit, including a magnetic core and a coil, a short-circuited conductor such as a ring of conducting material encircling at least part of the magnetic circuit and having the property of damping the rate of flux change in the said circuit to the degree necessary to just allow establishment of maximum flux at the desired point in the cycle. In this way the wave form is simply and effectively modified to that desired in the generator, whether of the high or low tension type.

In the adaptation of the invention to'a ma neto, for example, the damping ring is included in the magnetic circuit in such a way that the rate of flux change prior to closing of the circuit breaker results in the occurrence of the maximum flux at or close to the instant that the circuit is closed, whereby the prior voltage is kept too low to induce a premature spark.

Thus, in a conventional form of flywheel magneto having the usual stationary core structure around which the field structure rotates with the flywheel, the clampin device of this invention, either in the form of a closed ring or shortcircuited coil of conducting material like copper, surrounds one leg of the core and thus encircles at least part of the magnetic circuit to perform the function described. Advantage may be taken of the voltage induced in the coil by including in its closed circuit one or more electric devices, such as incandescent lamps, for example. In the other forms of magneto-electric generators, the damping ring is similarly placed in the magnetic circuit so as to encircle at least part of the same to provide the degree of damping required.

It will be seen that the simple and inexpensive damping device of this invention efiectively modifies the rate of change of the flux in the magnetic circuit to a degree such that unwanted impulses do not occur or are suitably modified, the degree depending upon the proportion of the magnetic circuit that the device encircles and the amount of conducting material comprising the device, which in turn depend upon the rate of change of flux desired in the magnetic circuit.

For a more complete understandin of the invention, reference may be had to the accompanying drawings, in which:

Figure 1 illustrates the adaptation of the invention to a conventional flywheel magneto structure, by way of illustration;

Figs. 2a and 2b are curves illustrating the modifying effect of the invention on the rate of change of the flux and the voltage, respectively, in the generating coil magnetic circuit of the magneto of Fig. 1; and,

Fig. 3 is a fragmentary view of the core structure of Fig. 1, and illustrates a modification of the invention.

Referring to the drawings in which the invention is shown as adapted to a conventional flywheel magneto, the latter includes a fleld structure carried by and rotating with the flywheel l anda stationary structure ii carrying the necessary coils, magnetic structure, breaker, etc. The field structure carried by the flywheel It may consist of'a circular permanent magnet I! having the air gap II between its north and south poles to which are attached the pole shoes II and II. The stator structure ll carries laminations of iron or other magnetic material formed with three legs, i8, i1 and II, which are united at their inner ends and extend more or less radially with their outer ends angularly spaced apart and curved to cooperate successively with the pole shoes I4 and II on rotation of the field structure on the fiywheel it in the direction of the arrow. The central leg I! of the core carries the primary and secondary coils is and 2|, respectively.

The primary coil is is arranged in a circuit which can be opened and closed by disengagement and engagement, respectively, of the cooperating breaker points 2! carried by the stator ii, one or which is mounted on a lever 21 engaging a cam 23 rotating with the flywheel ii, and normally urged against the cam 28 by the springs 24. The cam 23 normally holds the breaker points 2| open but allows the spring 24 to close them at a time when the leading pole shoe l overlaps the center leg I! and the other shoe H overlaps leg IS. The fiux established in one direction through the core is immediately followed by the building up of flux in an opposite direction through the core as the flywheel is rotated. A condenser 25 carried by the stator II is bridged across the breaker points II, as is usual. The structure and magnetic circuit just described are conventional and do not constitute the invention but serve to illustrate one type of magneto-electric machine to which the invention is applicable.

As is well known with this type of magneto, th flux through the spark coil first rises from zero to a maximum value in one direction, then reverses to a maximum value in the opposite direction, and finally returns to zero again as the flywheel is rotated with the contact points held open and no damping means provided. When the cam is allowed to open and close the breaker mechanism, the flux rises from zero to a maximum as before, since the contact points are held open until the maximum value has been reached, such as point A on the flux curve of Fig. 2a. At this point A the contacts close, thus completing the primary circuit and preventing the normal reversal of fiux through generation of primary current until point B is reached, when the contacts open, allowing the flux to change very rapidly from point B to point C. This induces a high voltage surge in the secondary winding, as indicated at point G on the voltage curve shown by Fig. 2b, which produces the desired spark at the spark plug in the engine. Since the original increase of flux from zero to maxi mum also links the secondary wind ng of the coil, this change of fiux also induces a peak of voltage proportional to the maximum rate of change of flux at this time, which is indicated at point D on Fig. 2a. At high rotat'ive speeds, the rate of change of flux at point D becomes sufiicient 1y great to induce in the secondary winding a high peak voltage value, as indicated at point F on the voltage curve of Fig. 2b. This peak voltage may be sufilcient to cause a spark to jump at the spark plug in the engine, thus producing the so-called maverick or early ignition discharge.

In order to so reduce the voltage at point F of Fig. 2b that a maverick spark is not produced at the spark plug, it is necessary to reduce the rate of change of the flux build-up indicated at point D of Fig. 2a. This is accomplished in accordance with the invention by encircling the leading leg of the stator core with a dampin coil or ring. The currents generated in this ring oppose the rapid change of flux and by proper proportioning of the ring, the flux curve may be made to approach that shown by the dotted line E in Fig. 2a, which is accompanied by a great reduction in the peak value of the maverick voltage generated, as is indicated by dotted curve H in Fig. 2b. This damping coil or ring does not materially aflect the performance or the desired spark, occurring at point 0 of Fig. 2b, since the leading leg of the core is not included in the operating circuit of the magneto at the time the contact points open. The device may consist simply of a copper strip encircling the leg I, as shown in Fig. 1. Other conducting materials may be used instead of copper if desired, such as silver, 'brass, aluminum, etc. The weight of the conducting material is determined by experiment as it depends upon the degree of Supp e s o 0 inclination of the dotted line slope E in Fig. 2a that is desired.

Operation of the damping device of this invention will be readily understood from the foregoing, the ring 2t encircling at least part of the magnetic circuit serving as a means for controlling or modifying the rate of change of the fiux in the magnetic circuit, with the eflect indicated by way of example in Fig. 2a, which in magnetos has the advantage of supressing or eliminating maverick sparking.

Instead of a single turn coil or ring 26, a shortcircuited coil, consisting of copper or other conducting wire with its ends soldered or otherwise electrically connected together may be used with equal facility. Because such a winding has a voltage induced therein, this voltage may be conveniently utilized to illuminate an incandescent lamp or for other purposes for which the surplus energy available is desired. Such an arrangement is indicated schematically in Fig. 3, wherein the coil 28 is short-clrcuited through the lamp 21 which accordingly glows when the magneto is in operation by reason or the voltage induced in the 001128.

Although a preferred embodiment of the invention has been illustrated and described herein. it is to be understood that the invention is not limited thereby but is susceptible of changes in form and detail within the scope of the appended claims.

I claim:

1. In a magneto for use in connection with internal combustion engine ignition systems, or the like, having spark plugs, or the like, with spark gaps, said magneto having a magnetic circuit including a magnet and pole shoe structure and a. relatively rotatable magnetic core structure having spaced arms intermittently bridged thereby, said core structure including primary and secondary windings on one of said arms, a circuit breaker for said primary winding for releasing a spark from the secondary winding across said gap, a member of conducting material of predetermined proportions mounted on said core and encircling a predetermined portion of said magnetic circuit for predeterminedly modifying the rate of change of the iiux traversing the same to an extent sufllcient for precluding premature sparking across said gap.

2. In a magneto for use in connection with internal combustion engine ignition systems, or

the like, having spark plugs, or the like, with spark gaps, said magneto having a magnetic circuit including a magnet and pole shoe structure and a relatively rotatable magnetic core structure having spaced arms intermittently bridged thereby, said core structure including primary and secondary windings on one of said arms, a circuit breaker for said primary windings for releasing a spark from the secondary winding across said gap, a member of conducting material of predetermined proportions mounted on said core and encircling another of said core arms for predeterminedly modifying the rate of change of the flux traversing the same to an extent suiilcient for precluding premature sparking across said gap.

3. In a magneto for use in connection with internal combustion engine ignition systems, or the like, having spark plugs, or the like, with spark gape, said magneto having a magnetic circuit including a magnet and pole shoe structure and a relatively rotatable magnetic core structure having spaced arms intermittently bridged thereby, said core structure including primary and secondary windings on one of said arms, a circuit breaker for said primary winding for releasing a spark from the secondary winding across said gap, a coil of conducting material of predetermined proportions mounted on said core and encircling another of said core arms for predeterminedly modifying the rate of change of the flux traversing the same to an extent sufiicient for precluding premature sparking across said gap.

4. In a magneto for use in connection with internal combustion engine ignition systems, or the like, having spark plugs, or the like, with spark gaps, said magneto having a magnetic circuit including a magnet and pole shoe structure and a relatively rotatable magnetic core structure having spaced arms intermittently bridged thereby, said core structure including primary and secondary windings on one of said arms, a circuit breaker for said primary winding for releasing a spark from the secondary winding across said gap, a short-circuited coil of conducting material of predetermined proportions mounted on said core and encircling another of said core arms for predeterminedly modifying the rate of change of the flux traversing the same to an extent suihcient for precluding premature sparking across said gap.

5. In a magneto for use in connection with internal combustion engine ignition systems, or the like, having spark plugs, or the like, with spark gaps, said magneto having a magnetic circuit including a magnet and pole shoe structure and a. relatively rotatable magnetic core structure having spaced arms intermittently bridged thereby, said core structure including primary and secondary windings on one of said arms, a circuit breaker for said primary winding for releasing a spark from the secondary winding across said gap, a short-circuited coil of conducting material of predetermined proportions having its ends electrically connected and mounted on said cor and encircling another of said core arms for predeterminedly modifying the rate of change of the flux traversing the same to an extent suflicient for precluding premature sparking across said gap.

6. In a magneto for use in connection with internal combustion engine ignition systems, or the like, having spark plugs, or the like, with spark gaps, said magneto having a magnetic circuit including a magnet and pole shoe structure and a relatively rotatable magnetic core structure having spaced arms intermittently bridged thereby, said core structure including primary and secondary windings on one of said arms, a circuit breaker for said primary winding for releasing a spark from the secondary winding across said gap, a member of conducting material of predetermined proportions mounted on said core and encircling another of said core arms in advance of said arm carrying said primary and secondary windings for predeterminedly modifying the rate of change of the flux traversing the same to an extent suillcient for precluding premature sparking across said gap.

'7. In a magneto for use in connection with internal combustion engine ignition systems, or the like, having spark plugs, or the like, with spark gaps, said magneto having a magnetic circuit including a magnet and pole shoe structure and a relatively rotatable magnetic core structure having spaced arms intermittently bridged thereby, said core structure including primary and secondary windings on one of said arms, a circuit breaker for said primary winding for releasing a spark from the secondary winding across said gap, a short circuited coil of conducting material of predetermined proportions mounted on said core and encircling another of said core arms in advance of said core arm carrying said primary and secondary windings i'or predeterminedly modifying the rate of change of the flux traversing the same to an extent sufficient for precluding premature sparking across said gap.

LLOYD H. SCO'I'I.

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

UNITED STATES PATENTS Number Name Date 1,331,998 Neuland Feb. 24, 1920 1,970,338 Roebel Aug. 14, 1934 2,128,044 Grabner Aug. 23, 1938 FOREIGN PATENTS Number Country Date 742,751 France Sept. 12, 1932

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