US3049644A - Ignition system - Google Patents

Description

Aug- 1962 o. E. BOWLUS ETAL 3,049,644

IGNITION SYSTEM Original Filed March 2, 1959 INVENT R. 077167 3 3,049,644 IGNITION SYSTEM Gmer E. Bowlus, Orchard Lake, and Kenneth A. Graham,

Birmingham, Mich, assignors to Chrysler Corporation,

Highland Park, Mich, a corporation of Delaware Continuation of application Ser. No. 796,448, Mar. 2,

. 1959. This application May 2, 1960, Ser. No. 26,374

- 8 Claims. (Cl. 315-419) The present invention relates to internal combustion engines and has particular reference to a new and improved ignition system therefor.

The present invention is an improvement over the ignition system of our Patent No. 2,819,428 and reference is also made to our copending application Serial N 0. 696,845, now Patent No. 2,984,760, filed November 15, 1957, relating to a surface gap spark plug which is described herein.

This application is a continuation of our application Serial No. 796,448 entitled Ignition System, filed March 2, 1959, now abandoned.

In the conventional ignition coil and magneto energized ignition systems for internal combustion engines wherein spark plugs are used having air gaps of a width within the range of 0.020 to 0.035 inch, the voltages necessary to electrically break down the air dielectric within these plug gaps fall within the range of 4 to 25 thousand volts. The high voltage spark is followed by a low current are of relatively long duration which is effective in igniting cold and/ or lean fuel mixtures but does not impinge upon carbon and lead fouling deposits which partially short the electrodes of these air gap plugs, nor contain the concentrated energy required to raise the temperature of the spark to a degree sufiicient to burn away these deposits on the insulator surface should the spark actually contact these deposits by internal flash over.

This lack of concentrated energy in the spark is due in part to the characteristics of the ignition coil and magneto energy sources which are characteristically slow in releasing their electrical energy. Their slow release of energy is particularly disadvantageous to ignition when sufiicient plug fouling exists to drain or shunt to ground a relatively large portion of the total energy supplied to the plug. Should fouling deposits of any substantial conductive capacity develop on the plugs the total energy dissipated by the shunting effect thereof may be suflicient to prevent the voltage from building up high enough to initiate a spark in the plug gaps.

Moreover, when using a conventional air gap plug of the type shown for example in Patent No. 2,269,067 with these ignition coil or magneto energizing systems, the spark plug actually has little opportunity to burn away its own fouling deposits since the spark does not occur in the immediate vicinity of these deposits which form on the insulator surface between the base of the center electrode and the metal shell or ground electrode of the plug. When these energizing systems on the other hand are used with surface gap plugs where a spark can be effective in burning away fouling deposits, the rate of release of energy to the plugs is not sufiicient to burn away the fouling deposits and also perform its fuel ignition function.

A major object of this invention, therefore, is to provide a condenser discharge ignition system with surface gap spark plugs to eliminate spark plug fouling by causing the spark to occur in the immediate vicinity of the fouling deposits and be sufficiently hot to burn said deposits away.

Another object is to provide an improved ignition system characterized by its ability to produce a spark of sumcient duration and heat to insure proper ignition of cold, lean and other combustion mixtures, and combustion of the fouling deposits.

Another object of the invention is to provide an improved ignition system which operates at a high frequency 3,049,644 Patented Aug. 14-, 1962 and low voltage compared to other systems known in the art.

A further object is to provide an ignition system capable of utilizing the residual energy of the ignition coil after the plug fires to maintain an are having suflicient heat to aid in burning away fouling deposits and in igniting all fuel mixtures.

A still further object of the invention is to provide an improved ignition system which is characterized by its ease of operation and its relatively few number of parts.

Essentially the invention relates to an improved ignition system utilizing conventional circuitry on the primary side of the ignition coil which delivers a relatively low frequency and low voltage power. The secondary circuit of the ignition coil is loaded by a secondary or ignition condenser and is connected through a series spark gap to a brush type distributor. The absence of rectifiers in the present system is particularly noted and the reasons therefor are described below. The distributor is connected in the conventional manner to a plurality of surface gap spark plugs generally of the type disclosed in the aforementioned patent application and described below. By employing such a system the series gap breaks down at a predetermined relatively low voltage and the charge which has been built up on the secondary condenser discharges to the spark plug being fired to produce a spark of very short duration which is sufficiently hot to burn away fouling deposits. Moreover, the absence of rectifiers in the system allows the residual energy of the coil to be used to recharge the secondary condenser to a progressively diminishing degree or continue an arc across the series gap and plug for a period of time suflicient to insure complete fuel ignition. The resistor 48 helps prevent recharging of the secondary condenser and allows continuous arcing. The ionized condition of the series and spark plug gaps allows the flow of current in the secondary circuit to maintain the plug arc until the energy decays to a level which will no longer support the arc.

Other objects and advantages of the invention will become apparent from the following description and drawings, in which:

FIGURE 1 is a schematic illustration of the electrical circuitry of the invention;

FIGURE 2 is a sectional view of the spark gap assemy;

FIGURE 3 is an elevational view of a distributor used in the system;

FIGURE 4 is a view of the brush type distributor cap interior contact surface taken along the line 44 of FIG- URE 3 in the direction of the arrows;

FIGURE 5 is a side elevational view of the brush type rotor;

FIGURE 6 is a top elevational view of the rotor of FIGURE 5; and

FIGURE 7 is a cross sectional view of the surface gap spark plug used in the present system.

Referring to the drawings and in particular to FIG 1, an ignition system is shown comprising a direct current power source 10 such as a battery or dynamo which is connected to ground and to an ignition switch 12 of the primary circuit 13. This switch is connected through a variable ballast resistor 14 to the primary winding 16 of a transformer or ignition coil 18. A pair of breaker switches 20 and 22'are connected in parallel with a spark suppressing and primary voltage build-up condenser 24 and are grounded at 26. Switches 20 and 22 represent the equivalent of the conventional breaker point contacts of ignition systems such as are shown in the aforementioned patent and alternately are opened and closed to produce a pulsating direct current in winding 16. Condenser 24 prevents excessive sparking at switches 20 and 22 and in the are.

series with winding 16 causes a high voltage oscillation in the primary circuit.

The flux change linking both winding 16 and winding 28 and caused by the collapse of the primary current when the points 20 and 22 are opened induces an oscillatory current flow in the secondary circuit 15 comprised partially of the secondary winding 28 of coil 18 which on the first quarter wave of oscillation energizes the secondary or ignition condenser 30 to a voltage of approximately 2-5 kilovolts. This condenser has one plate connected to ground and the other plate connected to said secondary winding and to a parallel arrangement of a main series spark gap 32 and a teaser spark gap 34. Teaser gap 34 is almost continuously ionized and tends to stabilize the voltage necessary to spark the main gap 32 at between 2,000 to 5,000 volts. The condenser 30 will charge up to the voltage necessary to spark gap series 32 and spark plug gap 42 which results in a high current flow in the secondary circuit to the plug.

As a result of this high current flow the are between the electrodes 44 and 46 of the surface gap plugs is very hot and is maintained for a very short time of approximately one microsecond. This hot arc occurs directly across the face of the dielectric separator 45 on which the fouling deposits occur and is particularly effective in burning these fouling deposits from this face and also in igniting lean fuel mixtures.

Following the secondary condenser discharge is a low current are maintained for approximately 250 microseconds by the residual energy of the coil 18. This residual energy is derived from continued oscillation of current in the primary circuit, while the points are open, caused by the electrical resiliency of primary condenser 24 as it alternately attains charge and loses charge and also by the self-inductance of primary inductor winding 16. This low current are is especially suitable for igniting certain cold and moisture laden fuel mixtures and continues until the voltage induced by this residual energy cannot support By so utilizing this residual coil energy to supplement the energy of the condensers initial discharge the size of condenser 30 may be held to a capacitance of approximately 1000 micromicrofarads which reduces condenser cost and also reduces the degree of arc erosion of the plug electrodes.

In order to prevent overly rapid dissipation of energy through the spark plug, to help in igniting cold fuel mixtures, to aid in reducing radio interference, and to help reduce electrode arc erosion, resistance or inductance 35 may be placed in the circuit. This resistor or inductance 35 also assists in maintaining the are at the spark plug after the initial discharge of condenser 30.

'I' he distributor 36 is provided with a brush type rotor 38 which in operation successively wipes across each high tension contact 40 at the moment that the required breakdown voltage of gap 32 is impressed across the secondary condenser 30. As condenser 30 discharges in an arc across series gap 32, the. surface gap spark plug 42 (see FIGURE 7) connected to the made contact 40 arcs through the fuel mixture from the center electrode insert 44 to the ground electrode insert 46.. The gaps 32 and 34 are shown in their structural form in FIGURE 2. and are contained in a unit 48 which is connected to the power lead 49 of the distributor 36. As shown in FIGURE 4, the contacts 40 are formed of conductive segments peripheral- 1y spaced around the cap 41 of distributor 36. The distributor rotor 38 as shown in FIGURE has a brush 50 for making sliding electrical contact with contacts 40, and a spring arm 51 electrically connected to brush 50 and adapted to make electrical contact with power inlet terminal 53 of the distributor.

Plug 42 is disclosed in further detail in applicants copending application Serial No. 696,845 and comprises an outer shell or ground electrode 52' of conductive material which is swaged or otherwise formed over at the end 54 to retain the inserts 44, 46 of molybdenum or other high temperature resistant metal and the dielectric insulator 45 which may be of porcelain or other insulative material known to the art. A center or power electrode 56 is spaced from the outer shell by insulator 58 and is provided with a collar 60 which holds dielectric insert 45 in place. Powdered insulator material 62 is compressed by the action of the assembly lock nut 64 to thereby properly position and maintain the plug parts in such position. As stated above, the voltage necessary to initiate the spark in the plug gap is approximately 2,000 volts which is considerably less than that required to are a conventional air gap spark plug.

We claim:

1. In an ignition system for an internal combustion engine, a surface gap spark plug and gapmeans in an operative electrical circuit, a condenser arranged in said circuit to discharge through said plug and gap means in series when the latter is conductive, said gap means requiring a predetermined comparatively high breakdown potential to initiate its conduction and being adapted to conduct thereafter at a comparatively low conducting potential until said conducting potential sustains a predetermined interruption, electrical power supply means arranged in said circuit to charge said condenser to said breakdown potential to elfect a sudden current surge across said gap means and plug upon the discharge of said condenser, and resistance means in said circuit for retarding the rate of discharge of said condenser appreciably as the potential of the latter approaches said conduction potential, said power supply means being also effective to supply electrical power to said gap means at said conducting potential for an extensive time interval with respect to the duration of said current surge, thereby to effect a trailing current of extensive duration across said gap means and plug following said initial current surge.

2. In an ignition system for an internal combustion engine, a surface gap spark plug and gap means in an operative electrical circuit, a condenser arranged in said circuit to discharge through said plug and gap means in series When the latter is conductive, said gap means requiring a predetermined comparatively high breakdown potential to initiate its conduction and being adapted to conduct thereafter at a comparatively low conducting potential until said conducting potential sustainsa predetermined interruption, electrical power supply means ar ranged in said circuit to charge said condenser to said breakdown potential to effect a sudden. current surge across said gap means and plug upon the discharge of said condenser, and resistance means in said circuit for retarding the rate of discharge of said condenser sulficiently as the-potential of the'latter approaches said, conduction potential to prevent said predetermined interruption of said conducting potential, said power supply means being also eifective to supply electrical power to said gap means at said conducting potential for'an extensive time interval with respect to the duration of said current surge, thereby to effect a trailing current of extenslve duration across said gap means and plug following said initial current surge.

3. In an operative ignition circuit for an internal combustion engine, surface gap means requiring a predetermined high breakdown potential to initiate conduction of electric current and being thereafter susceptible of conduction at a low conducting potential until the latter potential sustains a predetermined interruption, a surface gap spark plug arranged to receive the current conducted by said spark gap means, a condense'r'arr'anged to discharge through said plug and gap means when the latter is conductive, electrical power supply means for charging said condenser to said breakdown potential to effect a sudden current surge across said gap means and plug upon the discharge of said condenser, and resistance means for retarding the rate of discharge of said condenser sufficiently as the potential of the latter approaches said conducting potential to prevent said predetermined interruption of said conducting potential by resisting oscillation of said condenser potential about said conducting potential, said power supply means having a high internal impedance compared to the impedance to charging said condenser and being effective to supply electrical power to said gap means at said conducting potential for an extensive time interval with respect to the duration of said current surge to effect a trailing current of extensive duration across said gap means and plug following said current surge.

4. In an operative ignition circuit for an internal combustion engine, surface gap means requiring a predetermined high breakdown potential to initiate conduction of electric current and being thereafter susceptible of conduction at a low conducting potential until the latter potential sustains a predetermined interruption, a surface gap spark plug arranged to receive the current conducted by said spark gap means, a condenser arranged to discharge through said plug and gap means when the latter is conductive, electrical power supply means including a voltage step-up transformer having secondary windings connected with said condenser to charge the same to said breakdown potential to effect a sudden current surge across said gap means and plug upon the discharge of said condenser, and resistance means for retarding the rate of discharge of said condenser suficiently as the potential of the latter approaches said conducting potential to prevent said predetermined interruption of said conducting potential by damping oscillation of said condenser potential about said conducting potential, said power supply means being effective to supply electrical power to said gap means at said conducting potential for an extensive time interval with respect to the duration of said current surge to efiect a trailing current of extensive duration across said gap means and plug following said current surge.

5. In an operative ignition circuit for an internal combustion engine, surface gap means requiring a predetermined high breakdown potential to initiate conduction of electric current and being thereafter susceptible of conduction at a low conducting potential until the latter potential sustains a predetermined interruption, a surface gap spark plug arranged to receive the current conducted by said spark gap means, a condenser arranged to discharge through said plug and gap means when the latter is conductive, electrical power supply means for charging said condenser to said breakdown potential to efiect a sudden current surge across said gap means and plug upon the discharge of said condenser, said power supply means including a battery, a transformer having primary windings connected with said battery to be energized thereby and also having secondary windings connected with said condenser to charge the same, and breaker points for interrupting the energizing of said primary windings to effect a condenser charging potential across said secondary windings, and resistance means for retarding the rate of discharge of said condenser sufficiently as the potential of the latter approaches said conducting potential to prevent said predetermined interruption of said conducting potential by damping oscillation of said condenser potential about said conductin'g potential, said power supply means being effective to supply electrical power to said gap means at said conducting potential for an extensive time interval with respect to the duration of said current surge to effect a trailing current of extensive duration across said gap means and plug following said current surge.

6. In an operative ignition circuit for an internal combustion engine, surface gap means requiring a predetermined high breakdown potential to initiate conduction of electric current and being thereafter susceptible of conduction at a low conducting potential until the latter potential sustains a predetermined interruption, a surface gap spark plug arranged in series with said spark gap means, a condenser arranged to discharge through said plug and gap means when the latter is conductive, electrical power supply means for charging said condenser to said breakdown potential to efiect a sudden current surge across said gap means and plug upon the discharge of said condenser, and resistance means arranged between said gap means and plug in series therewith for retarding the rate of discharge of said condenser sufficiently as the potential of the latter approaches said conducting potential to prevent said predetermined interruption of said conducting potential by resisting oscillation of said condenser potential about said conducting potential, said power supply means being effective to supply electrical power to said gap means at said conducting potential for an extensive time interval with respect to the duration of said current sunge to effect a trailing current of extensive duration across said gap means and plug following said current surge.

7. In an operative ignition circuit for an internal combustion engine, surface gap means requiring a predetermined high breakdown potential to initiate conduction of electric current and being thereafter susceptible of conduction at a low conducting potential until the latter potential sustains a predetermined interruption, a surface gap spark plug arranged in series with said spark gap means, a condenser arranged to discharge through said plug and gap means when the latter is conductive, electrical power supply means including a voltage step-up transformer having secondary windings connected with said condenser to charge the same to said breakdown potential to effect a sudden current surge across said gap means and plug upon the discharge of said condenser, and resistance means arranged between said gap means and plug in series therewith for retarding the rate of discharge of said condenser sufficiently as the potential of the latter approaches said conducting potential to prevent said predetermined interruption of said conducting potential by resisting oscillation of said condenser potential about said conducting potential, said gap means being arranged between and in series with said resistance means and the connection between said condenser and secondary windings, said power supply means being effective to supply electrical power to said gap means at said conducting potential for an extensive time interval with respect to the duration of said current surge to eifect a trailing current of extensive duration across said gap means and plug following said current surge.

8. In an operative ignition circuit for an internal combustion engine, surface gap means requiring a predetermined high breakdown potential to initiate conduction of electric current and being thereafter susceptible of conduction at a low conducting potential until the latter potential sustains a predetermined interruption, a surface gap spark plug arranged in series with said spark gap means, a condenser arranged to discharge through said plug and gap means when the latter is conductive, electrical power supply means for charging said condenser to said breakdown potential to effect a sudden current surge across said gap means and plug upon the discharge of said condenser, said power supply means including a battery, a transformer having primary windings connected with said battery to be energized thereby and also having secondary windings connected with said condenser to charge the same, and breaker points for interrupting the energizing of said primary windings to effect a condenser charging potential across said secondary windings, and resistance means arranged between said gap means and plug in series therewith for retarding the rate of discharge of said condenser sufiiciently as the potential of the latter approaches said conducting potential to prevent said predeter-mined interruption of said conducting potential by damping oscillation of said condenser potential about said 7 e5 conducting potential, said gap means being arranged berent of extensive duration across said gap means and tween and in series with said resistance means and the plug following said current surge. connection between sa1d condenser and secondary w1nd- Referemes aged in the file of this patent ings, said power supply means being effective to supply electrical power to said gap means at said conducting 5 UNITED STATES PATENTS potential for an extensive time interval with respect to 2,819,428 Bowlus et a1. Jan. 7, 1958 the duration of said current surge to effect a trailing cur- 2,833,963 Tognola May 6, 1958

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