US2222498A - Ignition system - Google Patents

Description

Nov. 19, 1940.

IGNITION SYSTEM Filed April 13, 1939 2000 4000 6000 5 L7 L8 2. I 2.3 2-5 2.7 2.9

ENGINE R.P.M.

3nnentor w. A. BYCHINSKY 2,222,493

Patented Nov. "19, 1940 rom'rroN SYSTEM Wilfred A. Bychinsky, Ann Arbor, Micln, assitnor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application April 13, 1939, sci-a m. 207,713 1 Claim. (01. 123-l48) This invention has to do with an improvement in ignition systems for internal combustion engines and the like of the type in which the current fiowing through an inductance is suddenly 5 broken to obtain a sudden discharge of electrical energy for use in producing the spark. Such systems are commonly employed on present day automobile engines, the inductance taking the form of a transformer, commonly called a spark l0 coil, the primary circuit of which is interrupted to provide energy for the spark. The voltage of the discharge isstepped up by the transformer to enable it to jump the gap at the spark plug.

In another type of system, current through an inductance is interrupted and a condenser is arranged to store the discharge of energy following the break, the condenser being provided with a discharge circuit containing an electrical valve which breaks down upon application of suflicient voltage. In series with the valve is the primary of a step-up transformer which increases the voltage of the discharge. This type of circuit is characterized by the fact that the discharge is of high frequency as well as high voltage.

In both of the above' described ignition systems the inductances are fed with energy from a suitable source such as the conventional battery. A definite time is required for the current passing through the inductance to reach any particular 80 percentage of its steady value. The energy stored in the inductance and released when the current is interrupted depends on the value of the current at thetime of break. Hence, in such systems, as the speed of the engine increases and hence the length of time of the, circuit closing-opening cycle becomes shorter, the current builds up to lower and lower values and the energy available becomesless and less. As a consequence the high tension yoltage availableat 40 the spark plugs may become so reduced in value at high speeds as to seriously limit ignition performance. Conversely as the engine speed is reduced the current in the primary circuit increases and at low speeds may be large enough to produce destructive arcing at the contact points of the interrupter.

Another difficulty encountered with such systems is that under certain conditions when the engine is not running but the ignition switch remains closed there is a considerable discharge of current through the inductance and this, especially in the case of .the high frequency system described above, may be sufilcient to cause serious times disabling it.

The ideal ignition system r this type would be one in which the current through the inductance would build up to the same value regardless of 'engine speed. Such a system would produce a substantially constant energy output and would not produce excessive arcing at the interrupter points. I

I have discovered that this result may be substantially achieved by providing an automatically varying resistance in series with the inductance 1o in such a manner that the current always builds up to substantially the same value. Thus at top engine speeds low resistance is provided and when the engine is not running but the ignition switch is on, maximum resistance is provided. 15 The resistance must also be. capable of rapidly changing in value since the changes in engine speed which must be accommodated often take place very rapidly.

The resistance preferably takes the form of a, 20

fine wire in a gaseous atmosphere, for example a filament of substantially pure iron inan atmosphere of hydrogen. The ohmic resistance of such a unit varies directly with the'current flowing through it. Owing to the fineness of the 25 wire its. temperature changes very quickly with changes in current passing through it. Such resistances may be readily designed to hold the current within the desired limits insuring satisfactory ignition at all engine speeds.

In the drawing:

Figure 1 is a wiring diagram showing the application of my invention to a conventional battery ignition system.

Figure 2 is a wiring diagram showing the a 36 supplying current to the primary P of a conven- 45 tional spark coil through interrupter L the points of which may be protected by a small condenser C- as shown. R indicates a. ballast resistance arranged in series in the circuit. S indicates the usual secondary of the spark coil supplying en- 50 ergy through distributor D to spark plugs l0.

v The ballast resistance R preferably consists of a fine wire'of substantially pure iron contained ina sealed tube having an atmosphere of hydrogen. The tube may take the form shown in 55 Figure 5, l2 indicating the resistance wire anding of the contactsof'the interrupter 1, current hours through the primary circuit attaining a value depending length of time the circuit is closed and this in turn depends n the speed oi the engine, .the interrupter being driven at one-half enginespeed in the case ofa four cycle 'engine.- Should the speed of the engine be reduced the current in the primary circuit will tend to rise tcr'a higher maximum value because the circuit remains closed for a longer period but this tendency toward increase in current will be largely offsetj-by the increase in voltase drop through the resistance R due to'the fact that, as indicated by curve D of Figure 4, the resistance through It increases materially withvincrease in current. Should the enginespeed increase, the

current in the primary will tend to reach a low maximum value because -of the reduced time that the'contacts of the interrupter r are closed. This 1 tendency is,- however, offset by the fact that. the resistance of R. decreases with decrease in curof openingof the contacts. The values shown on the graphs may be readily calculated by those skilled in the art. Curve A, Figure 3, shows the value of current at break, this being maintainedv constant at substantially 2.15 amperes as above stated. .Ihis' condition is to be contrasted with that indicated by'curveA' showing the current at break in the same ignition system without the I It will be noted from A that the current falls offasthespeedincreases and at top speed is more than one-half an ampere below the value at low curv 'n shows them resistance of the primary circuit required to give the constant value of 2.15 amperes at, break. The total resistance is the sum offthe fixed resistance of the circuit plus the variable resistance of the ballast tube,

the latter giving the curve its drooping charac- Curve 0 shows the variations in average current through the primary circuit with changes in Curve D; Figure 4, shows the i'el'ation of the or .the design data resistance of the primary circuit. including the ballast tube. 'I'he increase in resistance-with increase in current is ballast tube.

There is shown in Figure 2 the application ofmy invention to an ignition system such as is deproduced by the action of the scribed and claimed in ,prior Patent 2,030,228

terrupter is providedv condenser 'C which is adapted to receive the energy stored in induct:

ance L when the interrupter is open. When the charge on condenser'C reaches the break-down voltage of the. gap in the two electrode eleotrici vaIveV currentflo'ws through vthe primary P of a transformer of which the secondary is indicated at S, the latter supplying high frequency current through distributor D -tospark plugs ill.

The ballast resistance operates in this circuit: In the same manner as in the circuit of Figure 1 to assist in the attaining" of substantially the same maximum current inthe inductance L under all operating conditions so as to give satisfactory and uniform ignition throughout the range of speed of the engine.

While I have described a. ballast resistor con sisting of a flne iron wire in hydrogen, many other types of constant current resistors may be employed. For example, a fine timgsten filament operating in vacuum will be found to be satisfactory when designed to have the proper operating characteristics.

I claim: In an ignition system, the combination of a s'ource of current, an inductance, a circuit breaker and a resistance in series, said resistance increasing-in value with increase inthe amount of current flowing through it, a condenser connected to saidcircuit so as to receive and store electrical energy from said inductance upon op-' ening of said circuit breaker, a gaseous discharge tube and the primary of a transformer in series with. said condenser, an ignition device connected to the secondary of 'said.transformer, said tube being adapted to break down when the charge on the condenserreaches a predetermined value;

thereby producing a high frequency discharge at w the ignition-device meansffordriving the circuit breaker at variablespeed, said resistance serving to maintain the current substantially constant at the time of opening of the interrupterv through

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