US2571788A - Electrical apparatus - Google Patents

Description

Oct. 16, 1951 TOGNQLA 7 2,571,788

ELECTRICAL APPARATUS I Filed June 9, 1949 IN VEN TOR.

ATTORNEY.

Patented Oct. 16, 1951 ELECTRICAL APPARATUS Tullio Tognola, Sidney, N. Y., assignor to Bendix Aviation Corporation, New York, N. Y., a corporation of Delaware Application June 9, 1949, Serial No. 98,092

12 Claims.

This invention relates to electrical apparatus and more particularly to means for producing sparks such as those employed in ignition systems for internal combustion and so-called jet or turbine engines.

One of the objects of the present invention is to provide a novel electrical system for producing a high-energy. high-frequency spark discharge at relatively low voltage across a p of practical dimensions.

Another object of the invention is to provide simplified means of light-weight construction which may be satisfactorily housed in a comparatively small space for producing a seriesof electrical sparks adapted for igniting a combustible mixture in the combustion chamber of an engine or the like. I

Still another object is to provide a novel ignition system for combustion engines or the like in which a low voltage is employed throughout the system, whereby electrical losses are materially reduced, the possibility of electrical failures is minimized and the requirements for radio shielding are greatly simplified. g

A further object is to provide an ignition circuit for combustion engines embodying a novel spark gap construction.

Another object is to provide a novel ignition.

circuit the functioning of which is not appreciably affected by the pressure and other atmospheric variations at different altitudes.

Still another object is to provide a novel method of producing electrical spark discharges between spaced electrodes.

A still further object is to provide an ignition system the operation of which is not seriously affected by ordinary fouling of the spark gap or by the presence of moisture at the gap.

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 drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention, reference for this latter purpose being had primarily to the appended claims.

In the drawings, wherein like reference char acters refer to like parts throughout the several views, I

Fig. 1 is a diagram of one form of novel electrical circuit embodying the invention, the source of energy being a magneto generator; and

Fig. 2 is a similar view illustrating another form of circuit energized by a battery.

The embodiment of the invention illustrated in Fig. 1, by way of example, is in the form of an ignition system for multi-cylinder combustion engines wherein a combustible charge is ignited by an electrical discharge across a spark gap. The energy source as shown consists of a ma neto which may be of any suitable known construction and comprises a magnetic rotor or flux distributor it) that cooperates in known manner with stator poles H to periodically energize the primary winding 12 of a transformer coil mounted on a core |3 bridging the stator poles. The ends of winding |2 are conventionally connected through a circuit breaker M which may be urged toward closed circuit position by a spring and periodically opened by the lobes of a cam |5 that is rotated in timed relation with rotor H]. A small condenser H5 is connected in shunt with the points of the circuit breaker to reduce sparking and the circuit of the primary winding is connected to ground at H.

The secondary winding I8 of the transformer is center tapped at [9 and connected to ground at I! while the ends thereof are connected to the input terminals of a full-wave point-toplane rectifier 20. If desired two half-wave rectifiers or any other suitable known type of rectifier may be employed. The alternate polarity energy generated in secondary winding I8 is thus supplied through the rectifier as uni-polar or unidirectional energy to a storage condenser 2|, one side of which is connected to the output of the rectifier. The other side of said condenser is shown connected to ground at 22. Energy stored in condenser 2| may be periodically released through a contactor 23, the points or contacts of which may be urged to open circuit posion by a spring and closed by a rotating cam 24 operated in timed relation to the engine. If timing of the sparks is not important, condenser 2| may be connecteddirectly to a terminal of the spark gap to be hereinafter described or other known means may be provided for controlling the discharge of the condenser. One contact of contactor 23 is connected to the high potential side of condenser 2| and the other contact is connected to the rotatable electrode 25 of a distributor 26 which is not a necessary part of the invention. The construction of the distributor may be in accordance with any of many known types in the ignition art. Distributor arm 25 should be synchronized with cam 24 but it is not necessary that either of 'these be synchronized with cam I5. If desired, the condenser 2| may be charged with a small high speed magneto as distinguished from one which operates at a speed comparable to that of the engine.

Each of the output terminals 21 of the distributor is conected to an electrode 28 of a novel spark gap construction, the other electrode 29 of which is connected to ground at 30. The gap 28, is may be of any desired shape and in one successful embodiment the same is circular, i. e., the electrode 28 consists of a disk concentrically disposed within a ring which. functions as the ground electrode 29. Disposed at one side of the gap and in contact with both electrodes is a resistor 3|. In the form shown the latter has a flat surface which bridges the gap, the same being of suitable resistance so that the initial surge of energy from condenser 2| causes, it is believed, a flow of current along said flat surface between the two electrodes. This flow of current is apparently effective to ionize the gap between the electrodes even under most adverse conditions, such as under water, thereby lowering the resistance of the gap and permitting a high-energy high-frequency spark to jump the gap at relatively low voltage, i. e., a voltage far below the normal spark-over voltage of the gap without the resistor 3|. The high-energy high-frequency spark discharge thus produced is also effective to drive out or discharge from the gap particles of lead, carbon or the like of the nature which eventually fouls the gaps of spark plugs which are now in common use.

In one successful embodiment of the abovedescribed circuit the maximum voltage generated was approximately 1,000 volts in comparison to present-day high voltage ignition systems wherein a potential of 16,000 to 18,000 volts must be generated in order to produce the 10,000 to 13,000 volts required at the spark plug. The capacity of condenser 2| was approximately .5 microfarads and the electrodes 28, 29 of a circular gap were spaced about .020 inch apart. The material of resistor 31 provided an ohmic resistance of about 10,000 ohms. The required resistance is somewhat dependent upon the shape of the gap and other circuit constants. If the ohmic resistance of the resistor is too small, the current will flow through it, instead of along the gap exposed surface thereof and ionization of and, hence, sparking across the gap itself will not occur. If said resistance is too large, the flow of current will be insufficient to effect ionization of the gap and hence no sparking will occur. Among many materials useful for making the resistance or semiconductive element 3|, fused mixtures of silicon carbide, iron powder or similar conductors and aluminum oxide or other ceramic binders have proved satisfactory. This resistance element may also be replaced by a ceramic or other insulator with sufiicient conductive material embedded in the surface or interstices thereof adjacent the spark gap.

The embodiment of the invention illustrated in Fig. 2 is of a form which has proved highly successful as an ignition system in so-called jet type engines. As shown the source of energy consists of a battery 35 which supplies the system preferably, but not necessarily, through a radio noise filter 36 comprising an inductance 31 and two condensers 34. The battery voltage which is usually about 24 volts may be stepped up to approximately 1,000 volts or other desired potential by means of a transformer comprising a primary winding 38 inductively coupled with a secondary winding 39. The circuit through the primary winding is completed through and periodically interrupted by a circuit breaker 40, one contact of which is connected to ground 4|. A condenser 42 may be connected in shunt with ed t0 numerous purposes.

4 the breaker to reduce sparking at the breaker contacts.

Circuit breaker 40 may be operated to closed position by a spring 43 or other suitable means and to open position by a rotatable cam 44. As shown said cam is of the single lobe type and is operated at a relatively high speed (about 7,000 R. P. M) by an electric motor 45 which may be energized from battery 35. Thus, the battery is permitted to intermittently energize primary winding 38 to thereby inductively energize secondary winding 39 at an increased potential. The ungrounded end of winding 39 is connected through a half-wave rectifier 46 to a storage condenser 41. In this embodiment the storage condenser preferably has a capacity of approximately two microfarads in order to produce a sufficiently high energy spark at the gap in the combustion chamber of the engine.

In the circuit illustrated, the ungrounded high potential terminal of condsener 47 is alternately connected to a pair of spark gaps 48 and 49 through two contactors 50 and 5|, respectively. The latter are operated by a single lobe cam 52 driven at relatively low speed (about 500 R. P. M.)

by motor 45 through suitable reduction gearing (not shown). As shown, these contactors are urged to closed position by springs and moved to open position by the cam 52. The spark gaps 48 and 49 may be of the same construction and operate in the same manner as the gap 28, 29 described above.

Condenser 4'! is being continuously charged by transformer 38, 39 through the rectifier 46. The charging rate is preferably sufficiently high to insure complete charging of the condenser during the interval between the opening of either of the contactors 50 or 5| and the closing of the other. When one of the contactors is moved to closed position, the condenser discharges across the corresponding gap in the same manner above described in connection with the embodiment of Fig. 1.

There is thus provided an extremely simple and a yet rugged electrical circuit which is novel and also highly useful particularly in the combustion engine ignition field. A system of the character provided can be constructed to fit in relatively small spaces of varied shapes and may be adapt- Additionally, there is provided a novel ignition system which requires but relatively small voltage for insuring a highenergy high-frequency spark discharge across a relatively wide gap under almost unbelievable conditions, the spark itself being effective to prevent the accumulation within the gap of foreign matter which would foul or short-circuit the same.

In a circuit of the type comprehended by this invention the width of the spark gap may vary quite markedly both above and below the dimensions of those found satisfactory in ignition circluits now in common use. The gap may be initially quite small and yet supply a suflicient amount of energy, so that considerable erosion can take place without rendering the gap inoperative. To say it differently, the gaps in the present system are far less sensitive than gaps 1 to melt or burn the same away or force them out of the gap before the fouling is suificient' to affect normal or satisfactory operation. The sys- 5. tom hereby provided is also much more efficient than prior high frequency systems because it eliminates the high frequency transformers heretofore used. Additionally, the present system employs a much smaller condenser than any prior comparable systems which will produce the same energy at the spark gap. The weight and space required are thus materially reduced. Another important advantage of an ignition system embodying this invention resides in the fact that leaner combustible mixtures may be fired in the engine cylinders by the high energy spark without detriment to high-speed high-power operation, thereby effectively reducing the operating cost and increasing the operating range of aircraft by reducing fuel consumption at cruising speeds.

Although only a limited number of embodiments of the invention are illustrated in the drawing and described in the foregoing specification, it is to be expressly understood that the invention is not limited thereto. For example, the sources of energy incorporated in the two embodiments illustrated in the drawing may be interchanged if desired and electrical energy may be taken from ather suitable sources. Neither is it necessary that, the source of electrical energy be of the high-frequency type, it being sumcient that the initial surge of current to the spark gap be comparable to that supplied by the discharging of the storage condensers in the systems described. Various changes may also be made in the design and arrangement of the parts illustrated as well as in the materials, electrical values, circuit constants, and speeds herein suggested as suitable without departing from the spirit and scope of the invention as it will now be understood by those skilled in the art. For example, the various voltages, resistances, capacities, gap dimensions and the like must be chosen to suit a given circuit for producing the desired energy under the prevailing conditions of operation. For a definition of the limits of the invention, reference is had primarily to the appended claims.

What is claimed is:

1. In an ignition circuit for combustion engines or the like, a storage condenser, a source of electrical energy for charging said condenser, a spark gap having a normal spark-over voltage in excess of the maximum voltage of the charge attainable by said condenser, an element having a high electrical resistance below the normal resistance of said gap connecting the electrodes of the latter, and means for connecting said gap in circuit with said condenser.

In an electrical circuit, a storage condenser, a source of uni-polar electrical energy for charging said condenser, a spark gap having a normal spark-over voltage greater than the voltage of the maximum charge attainable by said condenser from said source, means including a contactor for intermittently connecting the high potential terminal of said condenser with an electrode of said gap, and an electrical resistance element connecting said gap electrodes, said element being capable of conducting current between said electrodes during the initial discharge of said condenser whereby the spark-over voltage of the gap is momentarily reduced below the voltage of the charge stored in the condenser.

3. An electrical circuit comprising a storage condenser, a spark gap comprising a pair of spaced electrodes, means for connecting said gap 6. in circuit with said condenser, and means for causing said condenser to discharge across said gap when the charge -on the condenser reaches a predetermined voltage below the spark-over voltage of said gap, said last-named means including an electrical resistance bridging the electrode of the gap.

4. In apparatus of the class described, a source of electrical energy, a spark gap in circuit with said source, said spark gap being normally non-v conductive at the voltage supplied by said source, and means for rendering said gap conductive at said voltage including an electrical resistance element bridging said gap and having physical contact with both electrodes of the gap.

5. In electrical apparatus of the class described, a condenser, a source of electrical energy for charging said condenser, a spark gap in circuit with said condenser, said gap having a normal spark-over voltage greater than the voltage of the charge on said condenser, and means for momentarily reducing the spark-over voltage of the gap to permit said condenser to discharge across the same, said means including an element having surface contact with the electrodes of said gap and bridging the latter at one edge thereof.

6. In electrical apparatus of the class described, a source of high frequency electrical energy, a park gap in series with said source, said gap comprising a pair of electrodes in spaced relation to each other, and an element having high electrical resistance in contact with said electrodes and bridging the gap between the same.

'7. In apparatus of the class described, a storage condenser, means for charging said condenser including a magneto generator and a rectifier, a spark gap comprising spaced electrodes and having a normal spark-over voltage greater than the voltage of the charge supplied to said condenser, means including a periodically operated contactor for connecting said gap in circuit with said condenser, and means for causing said condenser to discharge across said gap including a semi-conductive element bridging the gap between said electrodes for initiating the flow of current therebetween.

8. In apparatus of the class described, a storage condenser, a source of electrical energy for supplying a unipolar charge to said condenser, said source including a battery, a transformer coil having the primary winding thereof in circuit with said battery, a circuit breaker for periodically interrupting the circuit through said primary winding, and means including a rectifier for connecting the secondary winding of the transformer to said condenser, a spark gap having a normal spark-over voltage greater than the voltage of the maximum charge supplied to said condenser by said source, means including a periodically operated contactor for intermittently connecting said gap in circuit with said condenser, means for operating said circuit breaker at one, speed and said contactor at a slower speed, and means for initiatin the discharge of said condenser across said gap including a high electrical resistor connecting the electrodes of said gap.

9. In an electrical circuit for creating a spark discharge, a direct current source of electrical energy, means including a transformer for stepping up the voltage of said source, a storage condenser connected to the secondary winding of the transformer, a spark gap adapted to be connected in eries with said condenser, the normal break-down voltage of said gap being greater than the voltage of the charge attainable by the condenser, and a resistor connecting the electrodes of said gap for conducting current from said condenser until the break-down voltage of the gap is reduced to that of the charge on the condenser.

10. Apparatus as defined in claim 8 wherein the means'for operating both circuit breaker and contactor comprise a single electric motor operably connected with said battery.

11. Apparatus as defined in claim 8 wherein the circuit breaker and contactor are actuated by separate cam means driven by a single electric motor operably connected With said battery.

12. Apparatus as defined in claim 8 including a plurality of said spark gaps and a separate contactor for connecting each said gap in circuit with said condenser, said contactors being" operable in predetermined succession by said operating means.

TULLIO TOGNOLA.

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

UNITED STATES PATENTS Number Name Date 1,459,252 Plumm June19, 1923 2,125,035 Smits July 26, 1938 2,180,358 Hooven Nov. 21, 1939 m 2,184,315 Peters et a1 Dec. 26, 1939 2,203,579 Randolph June 4, 1940 FOREIGN PATENTS Number Country Date 15 46,114 Norway June 16, 1939 873,716 France Apr. 7, 1942 227,000 Switzerland Mar. '7, 1943

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