US2482875A - Magnetogenerator - Google Patents

Description

Sept. 27, 1949. M. c. SAWYER memz'ro GENERATOR Filed June 30, 1944 INVENTOR.

HTTORNEY Patented Sept. 27,1949

2,482,875 MAGNETOGENEMTOB Marc 0. Sawyer, Otsego County, N. Y., assignor to Bendix Aviation Corporation, New York, N. Y., a corporation of Delaware Application J line 30, 1944, Serial N0. 542,908

This invention relates to electrical apparatus and more particularly to ignition means for internal combustion engines and current generating means therefor.

- One of the objects of the present invention is to provide a novel source of unidirectional electrical current which is adapted for use in ignition systems for internal combustion engines, or the like.

Another object of the invention is to provide novel current generating means which is suitable as a source of current in a condenser discharge type of ignition circuit.

Still another object is to provide a novelly constructed magnetogenerator which has suitable voltage output characteristics to make it adaptable for use in an internal combustion engine ignition system.

A further object is to provide novel current generating apparatus .which has good voltage regulation characteristics over a wide range of speeds.

A still further object is to providenovel apparatus of the above character which is selfcontained and independent of any outside electrical source for excitation.

The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for the purpose of illustration only and is not intended as a definition of the limits of the invention, reference for this latter purpose being had primarily to the appended claims.

The single figure of the accompanying drawing is a diagrammatic illustration of one form of magnetogenerator comprehended by the invention and shown in connection with one type of ignition circuit in which it is particularly advantageous.

The only embodiment of the invention shown in the drawing, by way of example, is in the form of a two-pole magnetogenerator which is particularly suitable for use in supplying electrical energy for an internal combustion engine ignition system of the type hereinafter described. As illustrated, the generator may comprise an armature or rotor provided with a plurality of windings 6 connected to a commutator l. The above parts of the contemplated structure may be constructed of any suitable materials and in any suitable manner well understood in the art.

The armature 5 may be driven by the engine 5 Claims. (01. 3221-50) on which the ignition system is installed, the speed ratio between the crankshaft and the armature being dependent upon the size of the generator in relation to the desired voltage at, all engine speeds.

Ordinarily, it is desirable in aircraft to use the smallest generator which can be relied upon to supply the desired voltages at safe operating speeds. In one suitable system, the armature isdriven at about three times crankshaft speed to obtain the desired voltage at idling and full speed. As the armature rotates in a magnetic field to be hereinafter described, current is generated in windings 6. This current is picked up from the commutator 1 and delivered as unidirectional current to a circuit by a pair of brushes 8 and 9 in a manner well understood in the art. As shown, brush 8 is connected by lead It to ground and brush 9 is connected by a lead II 'to the remainder of an ignition circuit.

In order that the magnetic field and, hence, the magnetic fiuxthrough armature 5 will be a maximum at zero speed, this field is created by one or more permanent magnets interposed between a pair of pole shoes l2 mounted adjacent to and on opposite sides of the armature. The pole shoes are preferably of laminated magnetic steel. In the'form shown, a bar magnet l4 engages each pole shoe H, the same being arranged so that the north pole of one magnet engages one pole shoe and the south pole of the other magnet engages the other pole shoe. The other opposite poles of the magnets may be magnetically connected in any suitable manner, such as by a magnetic flux conducting member l5 which may be the housing of the generator.

In the operation of the structure thus far de scribed, the voltage output of the generator will increase substantially as the speed of the armature increases. Novel means are accordingly provided for the purpose of materially reducing the maximum voltage output of the generator and yet insure the necessary voltage output at low or idling speeds and also minimize the change or variation in voltage output over a wide speedload range. Said means, as shown, comprises a shunt for the magnetic field of each magnet ll.

This shunt, in the illustrated structure. is accomplished by extending projections 16, It from the pole shoes l2 into air gap relation with member l5 to form an alternate or shunting flux path. The exact nature of the shunt will, of course, vary in differently constructed generators;

In order to vary the proportionate amount of the magnetic flux which flow in the main flux aseaavs path through the armature and in the shunt paths thus formed in accordance with the speed of the armature, a compensating or bucking field is created by means of coils l1, l1 wound on pole shoes l2, l2. These coils are preferably but not necessarily connected in series across the output terminals or brushes 8, 9 of the generator and so connected that the magnetic field set up around the same by the flow of current therethrough bucks the flow of magnetic flux from the magnets l4, l4 through the pole shoes l2, l2 and armature 5. In effect, the bucking coils increase the reluctance of the main magnetic flux path and causes a larger percentage of the flux from the magnets to fiow in the shunt paths. The effect of the bucking coils increases with speed because the current generated increases with armature speed.

The required number of turnsin each of coils I1 and the required reluctance of the shunting flux paths will vary in different systems depending on the results desired. In one practical em- .bodiment in which a voltage output of 300 volts was obtained at engine idling speed and about 450 volts at maximum speed-load conditions, 2000 .turns of No. 40 wire were used in each coil. This voltage range could be further reduced if necessary by properly proportioning the reluctance of the shunt and main flux paths. This may be done, for example, by changing the size of the air gap at the ends of projections Hi, i. e., in the shunting flux path, the cross sectional area of said projections or the character and size of coils IT.

The novel magneto generator thus comprehended is shown, by way of example only, as being connected in an ignition circuit wherein a discharge condenser l8 of approximately onehalf microfarad' capacity is operatively connected across terminals 8, 9, one side of the condenser being connected to ground and the other to brush 9. The ungrounded terminal of condenser I8 is connected to a terminal of a circuit contactor IS,

the movable contact of which may be periodically moved in one direction by suitable resilient means and in the other direction b means such as a rotating cam in a manner well understood in the art. The other terminal of the contactor is connected .to the end of the primary winding 20 of a high frequency transformer, the secondary winding 2| of which is connected in series with a spark plug 22.

Thus, when contactor I9 is open, condenser 18 will be charged by the generator. The primary circuit including the condenser, contactor and winding 20 is periodically closed at times when the condenser is charged, thereby permitting a high frequency discharge from the condenser through the primary winding. The rise and fall of the oscillating current in the primary winding causes current to be induced in Winding 2| at a sufiiciently high voltage to create sparks across the gaps of spark plug 22. The maximum voltage output of the generator is kept at a relatively low value, such as 450 [to 500 volts, to prevent arcing and, hence, unnecessary dissipation of energy at the contactor points as well as to prevent deterioration of said points. The generator must be designed, however, to provide ample voltage at idling speed. The voltage output range may be varied but a minimum of about 300 volts at engine idling speed permits the use of a relatively small transformer coil 20, 2| which may be readily incorporated in a radio shielded spark plug.

In a multi-cylinder engine, a plurality of par- 4 allel connected contactors each in a circuit with a transformer 20, 2| may be employed, as illustrated, means being provided for operating the contactors in timed sequence. If desired, however, one contactor and a suitable distributor may beprovided.

There is thus provided novel simplified ignition apparatus embodying a novelly constructed current generating means whereby a relatively small range of voltage output is obtained between maximum and idling engine speeds. The novel generator provided renders feasible and practical a low voltage distribution, high frequency ignition system wherein the danger of ignition failures at all altitudes is reduced to a minimum, as are also the radio shielding requirements of the system.

Although only a single embodiment of the invention is illustrated in the accompanying drawings and described in the foregoing specification, it is to be expressly understood that the same is not limited thereto. For example, the generator may be employed in various other ignition systems or the like and other types of current generating means may be employed in the ignition circuit shown. Various other changes may also be made particularly in the design and arrangement of parts illustrated and in the electrical values and materials mentioned above, by way of example, without departing from .the spirit and scope of the invention as the same will now be understood by those skilled in the art. For a definition of the limits of the invention, reference is had primarily to the appended claims.

What is claimed is:

1. In apparatus of the class described, a magnetic flux conducting rotor having windings thereon, a commutator operatively connected with said windings, a plurality of stationary pole shoes adjacent said rotor, permanent magnet means associated with said pole shoes whereby magnetic flux from said magnet means is caused to flow through said pole shoes and rotor, means shunting some of said magnetic flux away from said rotor, and means for decreasing the magnetomotive force across the armature magnetic circuit, said last-named means including a coil wound on each of said pole shoes and means including said commutator for electrically connecting said coils to said armature windings so that the magnetic fields set up by the flow of current through said coils tends to counteract the flow of magnetic flux to said rotor from said magnet means.

2. A magnetogenerator comprising a plurality of magnets having unlike poles connected by a flux conducting member, pole shoes connected with said magnets, a variable speed armature between said shoes, said shoes and armature being adapted to carry the magnetic flux, a shunt extending from a position between the magnets and shoes into flux conducting relation to said flux conducting member, and bucking coils between the shunt and the armature adapted for excitation by the generator whereby the proportion of flux deflected through the shunt may be increased as the speed of the generator increases.

3. A magnetogenerator comprising a plurality of magnets having unlike poles connected by a flux conducting member, pole shoes connected with said magnets, a variable speed armature between said shoes, said shoes and armature being adapted to carry the magnetic flux, a shunt extending from a position between the magnets and shoes into flux conducting relation to said i'lux conducting member, and means between the shunt and the armature adapted for excitation by the generator whereby the proportion of flux deflected through the shunt may be increased as the speed of the generator increases.

4. A magnetogenerator having magnets with unlike magnetic poles connected byaflux con ducting member, pole shoes and a variable speed armature adapted to carry the magnetic flux, a shunt extending from a position between the magnets and shoes into flux conducting relation to said flux conducting member; and means adapted to be excited'by. the generator to deflect an increasing proportion of flux through the shunt as the speed of the generator increases.

5. In apparatus of the class described a generator having a plurality of magnets with unlike poles connected by a flux conductor, pole shoes connected to the other poles of said magnets, a, variable speed armature positioned between the said pole shoe, and an interrupted flux conducting 'shunt circuit between the poles of each magnet and the pole shoes, and bucking coils in between the armature and, said shunt circuits, supplied with current from the armature to divert flux from the armature to the shunt circuits.

' MARC C. SAWYER.

REFERENCES CITED The followingre'ferences are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,024,225 Remy eta1. Apr. 23, 1912 1,527,641 Gilt Feb, 24, 1925 1,531,389 Gordon e- Mar. 31, 1925 1,622,145 Hunt Mar. 22, 1927 1,962,691 Landis June 12, 1934' FOREIGN PATENTS Number Country Date 20,225 Great Britain ......h..... 1912 176,091- Switzerland June 1'7, 1935

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