US2389640A - High frequency ignition system - Google Patents

Description

S. RUBEN Nov. 27, 1945.

HIGH FREQUENCY IGNITION SYSTEM Filed June 13, 1942 INVENTOR. damuel uen/ BY ///VEYS Patented Nov. 27, 1945 UNITED STATES PATENT OFFICE HIGH FREQUENCY IGNITION SYSTEM Samuel Ruben, New Rochelle, N. Y.

Application June 13, 1942, Serial No. 446,853

4 Claims.

This invention relates to ignition systems for internal combustion engines.

An object of the invention is to improve high voltage ignition systems.

Another object is to improve high altitude ignition systems, such as are used in aircraft, and to reduce or eliminate the ignition difliculties frequently encountered at high altitudes such as corona discharge and electric breakdown of the system.

A further object is to improve the operation of ignition systems under various conditions of spark plug fouling.

Other objects of the invention will be apparent from the following description and accompanying drawing taken in connection with the appended claims.

This application is a continuation-in-part of my prior filed co-pending application, Serial No. 437,322, filed April 2, 1942. ,l y

The invention comprises the features of construction, combination of elements, arrangement of parts, and methods of manufacture and operation referred to above or which will be brought out and exemplified in the disclosure hereinafter set forth, including the illustrations in the draw ing.

In the drawing:

Figure 1 is a circuit diagram of an ignition system for an internal combustion' engine embodying features of my invention;

Figures 2 and 3 illustrate modifications of part of the ignition circuit;

Figure 4 illustrates a temperature compensating feature applied to the ignition circuit;

Figure 5 is a diagram showing the preferred arrangement of the parts of the ignition circuit;

Figure 6 shows the construction of a condenser used in the circuit;

Figure 7 shows a temperature compensating auxiliary condenser which may be used in the circuit;

Figures 8 and 9 are top section and side views,

respectively, of a spark gap;

Figure 10 is a section through an induction coil used in the circuit; and

Figure 1l is an end view thereof.

The present invention relates to an improvement and simplification of ignition systems of the type described in my prior filed co-pending application mentioned above. In its preferred form it embodies the use of a low tension magneto for energizing a spark gap and utilizes a high frequency auto-transformer for applying the oscillations in the spark gap circuit to the ignition distributor circuits leading to the various spark plugs. The system is of lighter weight and less parts than the prior system.

One of the principal limitations on high altitude flying has beenv the difficulty of providing ignition systems for airplane engines which are not subject to electric breakdown due to the rarlcation of the air at high altitudes. The low atmospheric pressure at these altitudes permits corona discharges to develop between points of high potential difference. In high tension magneto systems the magneto may practically cease to function at times due to flash-over in the magneto itself. The high tension cables in the distributor manifold and leading from the magneto to the manifold also break down unless shielded in the proper .type of cables. The distributor is also subject to arc-over and disruption of proper timing at high altitudes.

The system of the present invention produces an ignition voltage of high frequency and steep wave front so as to effect sparking of the plugs even under conditions of adverse plug fouling.

The system also does away with the necessity for a distributor of the type using a spark gap y between the rotating contact and the stationary terminals and enables the substitution of a direct contact type of distributor. The distributor is not required to make and break any substantial current, however, as the spark voltage is generated only when the distributor is in the middle of its contact position with any of the stationary terminals.

The system also allows the use of larger sizes of spark plugs for all operating conditions, thus improving the maximum power development of the engine during take-off and other periods of peak performance requirements.

In the past where high frequency systems have been used they have depended upon the use of a high frequency transformer to apply the voltage to the spark plug. This required a fairly high voltage transmission to the primary to avoid excessive or impractical transformer ratios and, unless the transformer was close to the plug, insulation and distributed capacity losses were substantial. In the present system a high potential is developed across the spark plug electrodes by use of a resonant circuit. However, due to the arrangement of the resonant circuit elements in relation to the high frequency energy source and the spark plugs, the main part of the circuit is operated at low voltage. Thus the voltage on the distributor and in the manifold is kept at 'a low va1ue,sueh as 1,500 volts, where arc-over or breakdown of the insulation at high altitudes does not take place.

Referring to the drawing the ignition system shown in Figure 1 comprises a low tension magneto I2 preferably of the inductor type for producingv periodic discharges across a spark gap I3 connected in an oscillatory circuit comprising a condenser I4 and an inductance I5. The high frequency oscillations in this circuit are distributed by distributor I6 to the various spark plug circuits in sequence such as circuit I1 containing series condenser I8 and an inductance I9 which is connected in shunt with the electrodes of spark plug 28.

The magneto may be of well known type comprising a permanent magnet which rotates past the poles of a stationary core 26 upon which the f.

primary and secondary magneto windings 21 and 2'8 are wound. The magneto mechanism includes a rotating cam 2l geared to the engine, the gear ratio and the number of cam points being related to close and open cooperating contacts 22 each time a, spark, is required at one of the spark plugs. Upon each opening of contacts 22 the p1'i mary current is interrupted causing a sudden collapse in flux which induces a voltage impulse across magneto secondary 28 which charges condenser I4 through low impedance coil l5 to a voltage sufficient to produce a breakdown of gap I3. Breakdown of the spark gap produces high frequency oscillations in Vthe oscillatory circuit comprising condenser I4 and inductance l5. 'I'he oscillatory voltage developed across inductance I is of comparatively low value, for example about 1,500 volts peak.

Rotating arm 23 of distributor I6 is driven by the engine at such speed as to connect one of the spark plug circuits I'l each time a spark is required at its associated plug. Accordingly, at the instant when a magneto impulse is produced by the action of cam 2l resulting in breakdown of spark gap i3 and Vhigh frequency oscillations in the oscillatory circuit; the pinion gear contact 2li on the end of distributor arm 23 is in positive contact with one of the segments 25 of the stationary part of the distributor, which segment is connected to one of the spark plug circuits Il. A wiper contact may be used in the distributor in place of the pinion gear, if desired.

'Ihe low voltage oscillations of high frequency developed across inductance I5 is thus applied to the individual spark plug circuits in sequence. The series condenser I8 and the inductance I8 individual to each of these circuits, when connected by the distributor to the end of inductance I5, form with it a resonant circuit which is tuned to resonate at the frequency of the oscillations generated in the oscillatory circuit, associated with the spark gap. These oscillations result in the creation of a high oscillatory voltage across inductance I9 and hence across the electrodes of spark plug 20 producing a spark thereat. However, the peak voltage developed at the distributor and in line I1 remains comparatively low, such as about 1,500 volts, due to the phase relations in the circuit. The peak voltage developed across each of the resonance circuit components is 10,000 to 15,000 volts dependent upon the eiiiciency of those elements.

Figure 2 illustrates a modification of the circuit in which the inductance I9 is connected in series with line I'l leading to the spark plug and capacitance I8 is connected across the spark plug electrodes. With this circuit the energy of the spark discharge per oscillation is somewhat greater.

Whether the circuit of Figure 1 or that of Figure 2 is used will depend in part upon the permissible amount of spark plug wear or erosion.

It is also possible to utilize a step-up transform- 5 er in connection with the resonant circuit as shown, for example, in Figure 3, wherein the prif mary 30 of a high frequency transformer is connected in series with condenser I8 and the secondary 3| is connected in shunt with the spark plug electrodes. The transformer may, in some cases, be in the form of a step-up autotransformer. I

When the ignition system is exposed to wide variations in temperature, such as from 40 C. l5 to +40 C., changes in the dielectric constant of the cable and the other parts of the system will aect the resonant frequency of the oscillatory circuits.` The circuit'elements may be designed and constructed to minimize or compensate for l this effect. For instance, Condensers may be used having dielectrics whose dielectric constant varies with temperature in such a manner as to maintain the resonance condition of the circuits. Thermostatic control means may also be used. Figure i illustrates one type of thermostatic compensation which comprises a fiat universal wound inductance coil 35, mounted on base 38 and connected in series with the oscillatory spark gap circuit and having a powdered iron core element 36 supported on a thermostatic loi-metal element 3l for varying the inductance of the coil with variation in temperature conditions to maintain the optimum resonance conditions. Figure 4 also illustrates that inductance I5 which is, in effect an auto-transformer, can be connected as a step-up (or step-down) transformer.

Figure 5 illustrates a suitable arrangement for the parts of the ignition circuit. The casing 40 contains the magneto, the spark gap, the oscil- 40 lation coil and condenser and the distributor,

shaft 4I being driven by the engine. The segments 25 of the distributor are connected to the conductors of the cable manifold winch may be r shielded in a well-known manner.' Condensers I8 4" may be connected .in series with the conductors of the cable manifold nealthe spark plugs and inductance coils I9 may be enclosed in copper sheaths and mounted on or madepart of the spark plugs themselves, or also be mounted in the manifold. In some cases the coils I9 may be inserted inside the glass tube comprising condensers I8.

Condenser I8 may be constructed as illustrated in Figure 6 of a Pyrex glass tube 50 having inside and outside conductive coatings 5I and 52 which form the condenser electrodes. The coatings may be made by grinding precipitated silver with about v 7% polystyrene and forming a varnish with xylol as a solvent. This is painted on the tube leaving wide margins at the tube ends. The coating is then baked and then electroplated with a thin layer of copper to insure continuity and strength. In order to reduce edge eiects, a pair of cupped metal rings 53 are inserted inside the tube at the ends of the electrode area prior to the application of the inner silver varnish coating. The wedge shaped annular grooves formed by the rings and the glass tube walls are iilledv with an insulating Varnish 54. Contact may be made to the inner electrode by a spring clip 55. Y

Figure 7 illustrates a compensating auxiliary condenser 60 which may be connected in shunt with lcondenser I4 for temperature compensation ii' desired. Condenser 60 comprises a sheet metal electrode 6I clampedag'ainst the face of a ceramic plate I2. The other condenser electrode 6l is formed of thermostatlc bi-metal which is clamped on top of electrode 8| with a mica sheet 64 between them. Thermostatic electrode Il is clamped only at one edge so that temperature variations will produce variations in spacing between the free edge of the electrode and the stationary electrode 6 I thus varying the capacity.

Figures 8 and 9 illustrates a suitable form of spark gap I3. This comprises a pair of copper rods 10, each having a flange 1| near one of its ends and a recess in the end containing a tungsten rod the end of which form the active electrode surface of the spark gap. Copper rods 10 are clamped in suitable brackets 12 on a base plate 1I with the ends of tungsten electrodes 14 in opposed spaced relation. A sleeve l formed of a short length of Koroseal tubing or similar material is forced over the ilanges 'H on the copper rods to thereby inclose the sparkgap area. A copper tube 16 is forced over the Koroseal tubing to prevent bulging of the Koroseal at high altitudes where the internal pressure will exceed atmospheric pressure. I have found that this spark gap construction will withstand large atmospheric changes in pressure and afford satisfactory operation under widely varying conditions.

Flgures and 1l illustrate the preferred conastruction for inductance coil i9. The coil is made up of a set of four universal wound coil sections 90 on a suitable coil form having a powdered iron core 9| and a powdered iron cup $2 forming a return path inclosing the coil sections. An eccentrically mounted core piece 93 is secured to the free end of core 9i and may be adjusted to vary the gap in the magnetic circuit. This permits accurate adjustment in the resonant frequency of the circuit.

Suitable values for the circuit elements can readily be chosen by those skilled in the art when an operating frequency is decided upon and the distributed capacitance and inductance of the system taken into account. Since the inductanoes Il can fbe varied after assembly by addusting pole segments 03, it is readily possible to arrive at the approximate values for the capacitances and inductances by computation and then make final adjustments after the system is assembled and tested. The other parts can also be adjusted or-replaced until perfect resonanceA is achieved.

In one system a magneto delivering between 1,500 and 2.000 volts was used. Condenser I4 had a value of .00403 microfarad, inductance Il a value of 75 millihenries. The circuit oscillated at 296 kilocycles. Inductance il and capacitance Il were arranged as shown in Figure 2 and had values of 2.1 millihenries and 125 nuoro-microfarads. respectively.

While the present invention. as to its objects andadvantages,hasbeendescribednereinascar ried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. An ignition system for an internal combustion engine comprising a magneto, a tuned oscillatory spark gap circuit excited thereby, a current distribution -circuit fed by said oscillatory circuit comprising a distributor and a plurality of individually tuned spark plug branch circuits tuned to the frequencies of said oscillatory spark gap circuit, each of said spark plug circuits including reactive resonant circuit elements and a spark plug connected between points of high resonant potential difference' in said circuit.

2. An ignition system for an internal combustion engine comprising a low tension magneto, a high frequency tuned oscillatory spark gap circuit excited thereby, a. low tension current distribution circuit fed by said oscillatory circuit comprising a distributor and a plurality of individual spark plug work circuits connected in sequence to said oscillatory circuit by said distributar, each of said spark plug circuits including resonant circuit elements, forming, when connected by said distributor to said oscillatory circuit, a branch circuit resonant at the frequency of said tuned oscillatory circuit, whereby a high oscillatory potential diilerence is developed across a pair of terminals in said spark plug circuit, and a spark plug having its electrodes connected to said terminals.

3. An ignition system for an internal combustion engine comprising a magneto, a spark gap connected across the output terminals thereof, a series arrangement of capacitance and inductance also connected across said terminals, and a current distribution circuit connected to a point located between said capacitance and at least part Yoi! said inductance, said distribution circuit comprising a distributor and a plurality oi' individual spark plug circuits connected to said point in sequence by said distributor, each of said spark plug circuits including a series arrangement of capacitance element and inductance element and a spark plug connected to receive the oscillatory energy across one of said elements.

4. An ignition system for an internal combus tion engine comprising a magneto,a spark gap connected across the output terminals thereof, a series arrangement oi' capacitance and inductance also connected across said terminals, and a current distribution circuit connected to a point located between said capacitance and at least part of said inductance, said distribution circuit comprising a distributor and a plurality oi individual spark plug circuits connected to said point in sequence by said distributor. each o! said spark plug circuits including a series arrangement of capacitance element and inductance element and asparkplugconnectedacrossoneofsaidelements.

SAMUEL RUBEN.

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