Spark plug apparatus and internal combustion engine ignition systems including same

Abstract

 Spark plug apparatus includes a spark-enhancing construction operative during the time between sparks to create spark-enhancing conditions for the sparks. In one type of construction, a corona wind is produced in the air gap to direct the ignited mixture away from both electrodes in order to reduce heat loss from the ignited mixture by heat transfer to the electrodes. In a second type of construction, a plasma cloud is produced in the air gap enhancing the production of the sparks.

Description

[0001] The present invention relates to spark plug apparatus, and also to an internal combustion engine ignition system including such apparatus.

[0002] Considerable efforts have been devoted during the past decades to improving the efficiency of converting chemical energy to thermal energy by combustion, and particularly to the problem of burning an air-fuel mixture in an internal combustion engine in a manner introducing a minimum quantity of pollutants into the atmosphere. These pollutants include nitrogen oxides, carbon monoxides, and unburnt hydrocarbons (hereinafter called "HC"), namely hydrocarbon molecules which have not been completely oxidized. Reducing the level of HC emission is important not only to reduce hazardous air pollution, but also to improve the combustion efficiency, and thereby to reduce fuel consumption.

[0003] The major parameters which contribute to a higher level of HC emission are low flame speed, poor ignition process which may lead to a misfire cycle, and non-homogeneous charge. Different mechanisms for misfire have been observed. In one observed mechanism, the flame does not move away from the electrodes, and therefore there is substantial heat loss from the spark kernel to the electrodes which causes the spark kernel to grow so slowly as to cause a misfire. A misfire cycle results in a considerable amount of HC emission.

[0004] According to a broad aspect of the present invention, there is provided spark plug apparatus for an internal combustion engine comprising: an electrode system including a high-voltage electrode and a ground electrode spaced therefrom to define an air gap into which a combustible mixture is to be introduced; and a high-voltage source for applying, during time-spaced intervals, high-voltage pulses between said high-voltage and ground electrodes to produce sparks in said air gap to ignite the combustible mixture therein; characterized in that the apparatus further includes spark-enhancing means operative during the time between sparks to create spark-enhancing conditions for the sparks when produced by said electrodes.

[0005] When an intense electric field is produced between two electrodes at low pressures, a glow discharge occurs between the two electrodes. At higher pressure, about atmospheric or higher, a corona discharge occurs particularly when one of the two electrodes has a shape, such as a pointed tip, causing the electric field at its surface to be significantly greater than that between the two electrodes. The corona discharge is usually evidenced by a faint glow enveloping the high-field (e.g., higher-voltage) electrode, and is accompanied by a flow of electrically-charged particles, called a "corona wind", directed from the high-voltage electrode towards the ground electrode. When the electric field is increased in intensity, a "plasma cloud" is produced, namely a cloud of electrically-charged particles having a considerably higher density, several orders of magnitude higher, than in a corona discharge.

[0006] The present invention exploits the above phenomena, during the time between sparks, to create spark-enhancing conditions for the spark when produced by the electrode system.

[0007] Thus, according to one implementation of the invention, the electrode system is controlled during this interval between sparks to produce a corona wind in the air gap which, when the spark is produced, directs the ignited mixture away from both the high-voltage and ground electrodes in order to reduce heat loss from the ignited mixture by heat transfer to the electrodes. This enhances the growth of the spark kernel and thereby increases the ignition efficiency of the gas mixture and decreases the possibility of a misfire.

[0008] According to a second implementation of the invention, the electrode system is controlled so as to produce, during this time interval, a "plasma cloud" in the air gap. This plasma cloud aids in the formation of the spark, and also enhances the growth of the spark kernel when produced between the high-voltage and ground electrodes. It thereby also increases the ignition efficiency of the gas mixture and decreases the possibility of a misfire; and further, it lowers the voltage required in order to produce the spark kernel.

[0009] According to another aspect of the present invention, there is provided an ignition system for an internal combustion engine, including spark plug apparatus constructed in accordance with the foregoing features for increasing engine efficiency and/or lowering toxic HC emissions.

Fig. 1 is a side elevational view illustrating one form of spark plug constructed in accordance with the present invention;

Fig. 2 is an enlarged view of the electrode structure in the spark plug of Fig. 1, with parts broken away to more clearly show internal structure;

Fig. 3 is a simplified schematical diagram illustrating the electrical ciruit for producing a corona wind in the two-electrode system of Figs. 1 and 2;

Fig. 4 is a timing diagram helpful in explaining the operation of the electrical circuit of Fig. 3;

Figs. 5 and 6 are side elevational views illustrating the electrode structure of two further forms of spark plugs constructed in accordance with the present invention;

Fig. 7 is a bottom plan view of the electrode structure in the spark plug of Fig. 6;

Fig. 8 is a simplified schematical diagram illustrating the electrical circuit for the three- electrode system of Figs. 5-7;

Fig. 9 is a side elevational view illustrating the electrode structure of a three- electrode spark plug for producing a "plasma cloud" in the air gap to enhance the formation and growth of the spark kernel;

Fig. 10 is a simplified schematical diagram illustrating the electrical circuit for the spark plug of Fig. 9;

Fig. 11 is a timing diagram helpful in explaining the operation of the circuit of Fig. 10;

and Figs. 12 and 13 are fragmentary views illustrating two further spark plugs constructed in accordance with the present invention.

[0010] The spark plug illustrated in Figs. 1 and 2 of the drawings, therein generally designated 2, may be of a conventional construction such as commonly used in internal combustion engines, except for the high-voltage electrode 4 and the ground electrode 6 producing the air gap 7 in which the combustible mixture to be ignited is introduced. Thus, in the spark plug illustrated in Figs. 1 and 2, the high-voltage electrode 4 is of rod configuration and is formed with a pointed tip 4a, whereas the ground electrode 6 is of cylindrical configuration enclosing the high-voltage electrode 4 and formed with a pair of windows 6a, 6b on diametrically- opposite sides aligned with the air gap 7.

[0011] The electrical circuit for energizing the two electrodes 4, 6 is schematically shown in Fig. 3. It includes a high-voltage source 8 for applying, during time-spaced intervals, high-voltage pulses (Vg) between the high-voltage electrode 4 and the ground electrode 6 to produce sparks in the air gap 7 and thereby to ignite the combustible mixture.

[0012] The electrical circuit illustrated in Fig. 3 includes a further voltage source 10 which applies constant current (i_cor) continuously to the two electrodes 4, 6. The magnitude of the current supplied is sufficient to produce a corona discharge from the high-voltage electrode 4, and thereby a "corona wind". The so-produced corona wind tends to flow through the two windows 6a, 6b in the ground electrode 6, and thereby directs the ignited mixture, or spark kernel, away from both electrodes. The effect is to reduce the residence time of the spark kernel near both of the electrodes, and thereby to reduce the heat loss from the spark kernel by heat transfer to the electrodes. The result is to improve the ignition of the combustible mixture such as to lower the HC emission, as well as to reduce fuel consumption.

[0013] The timing diagrams of Fig. 4 more particularly illustrates the operation of the electrical circuit of Fig. 3. Thus, the voltage source 10 produces constant current (i_cor) continuously to the two electrodes to produce a continuous corona wind, such that when the high-voltage source 8 outputs a periodic pulse Vg between the two electrodes 4, 6 to produce a spark in the air gap between the two electrodes, the existing corona wind moves the spark kernel away from the two electrodes. The power supply 10 is shown in Fig. 4 as producing sawtooth voltage pulses V_cor.but it will be appreciated that this is merely a schematical representation as the actual waveform of these voltage pulses is according to a complex function of time dependent on the change in pressure in the cylinder.

[0014] The electrical circuit illustrated in Fig. 3 further includes a diode 12 which protects the auxiliary supply 10 from over-voltage from the main supply 8. If the auxiliary supply 10 includes a high-voltage damping resistor, diode 12 would not be necessary.

[0015] The circuit illustrated in Fig. 3 is a simplified electrical circuit which can be used with the spark plug of Figs. 1 and 2. It will be appreciated that this electrical circuit could include a feedback loop causing voltage Vor to vary according to the dielectric strength of the gap in order to produce a constant current (i_cor) of uniform magnitude, and thereby to obtain maximum corona wind velocities continuously within the air gap.

[0016] While the circuit and diagrams of Figs. 3 and 4 have been described above particularly with respect to the spark plug of Figs. 1 and 2, it will be appreciated that they are also applicable to the spark plugs to be described below, as well as to the spark plugs of other constructions, including conventional constructions.

[0017] Fig. 5 illustrates another spark plug construction, generally designated 22, wherein the high-voltage electrode 24 is also of rod configuration terminating in an end section 24a having a pointed tip, but in this case the end section is bent perpendicularly to the longitudinal axis of the electrode. The ground electrode 26 is also of rod configuration, and is provided with an end section 26a also having a pointed tip bent to be parallel to end section 24a of the high-voltage electrode 24. The two end sections 24a, 26a are spaced from each other to define an air gap 27 into which the combustible mixture is introduced.

[0018] The spark plug illustrated in Fig. 5 may be energized by a similar circuit as schematically illustrated in Fig. 3. Thus, the constant current (i_cor) continuously supplied by voltage source 10 produces a continuous corona wind within the air gap 27, which moves in the direction shown by arrow 28. When the high-voltage pulse is applied by source 8, this corona wind moves the ignited gas mixture, or spark kernel, away from both of the electrodes 24, 26, thereby reducing the heat loss from the spark kernel by heat transfer to the electrodes, and improving the combustion of the mixture.

[0019] While Fig. 5 illustrates the end sections 24a, 26a of the two electrodes as being perpendicular to the longitudinal axis of the spark plug, the end section may be parallel to the spark plug longitudinal axis, or at any angle in between.

[0020] Figs. 6 and 7 illustrate a spark plug, generally designated 32, of more conventional configuration, including a high-voltage electrode 34 and a ground electrode 36 defining an air gap 38, but further including an auxiliary electrode 39 for continuously producing the corona wind. Thus, the auxiliary electrode 39 is also of rod configuration extending parallel to the high-voltage electrode 34, but the end of the auxiliary electrode is bent towards the air gap 38.

[0021] In the example illustrated in Figs. 6 and 7, the bent-end of the auxiliary electrode 39 is divided into two sections 39a, 39b which straddle the opposite sides of the two electrodes 34, 36. The two sectors are oriented in a converging relation, as shown particularly in Fig. 7, so as to produce a corona wind which directs the spark kernel away from the two electrodes 34, 36. As a result, there is better ignition of the combustible mixture when the spark is produced in the air gap 37 between the two electrodes 34, 36.

[0022] Fig. 8 schematically illustrates the electrical circuit that may be used with the three electrode system illustrated in Fig. 7 including the auxiliary electrode 39. The electrical system illustrated in Fig. 8 is the same as, and operates in substantially the same manner as, that illustrated in Fig. 3 for a two-electrode system, except that in the Fig. 8 arrangement the constant current, continuously generated by voltage source 10, is applied between the auxiliary electrode 39 and the ground electrode 36 to produce the continuous corona wind which improves the combustion of the mixture.

[0023] As shown in Figs. 6 and 7, the tips of the two bent sections 39a, 39b of the auxiliary electrode 39 are preferably pointed in order to enhance the corona discharge, and thereby the corona wind, but this is not essential.

[0024] Preferably, V_cor of voltage source 10 should be 2 to 10 kV; and Vg of voltage source 8 should be from 15 to 25 kV. Good results were obtained when V_cor was 7 kV, and V₁g was 18 kV.

[0025] Fig. 9 illustrates a spark plug construction in which the ignition is improved by the provision of an auxiliary electrode which produces a "plasma cloud" to enhance the formation and ground of the spark in the air gap when generated by the high-voltage pulse.

[0026] Thus, the spark plug illustrated in Fig. 9, therein generally designated 42, includes a high voltage electrode 44 and a ground electrode 46 of conventional construction, and an auxiliary electrode 49 having a pointed tip 49a adjacent to the air gap 48 between that ground electrode 46 and the high-voltage electrode 44. Fig. 10 illustrates the electrical circuit that may be used with the spark plug of Fig. 9; and Fig. 11 illustrates the timing diagrams applicable to that electrical circuit.

[0027] The electrical circuit includes a voltage source 48 for applying, during time-spaced intervals, high-voltage pulses (Vg) between the high-voltage electrode 44 and the ground electrode 46. The electrical circuit further includes an auxiliary voltage source 50 which applies auxiliary voltage pulses (V_aux) between the auxiliary electrode 49 and the gound electrode 46 just before the application of the high-voltage pulses Vg, as shown in the timing diagram of Fig. 11.

[0028] The application of the auxiliary voltage pulses (V_aux) produces a plasma cloud of highly ionized particles that extends into the air gap between the high-electrode 44 and ground electrode 46, as shown in Fig. 9, so that as soon as the high-voltage pulse Vg is applied by voltage source 48, the plasma cloud enhances the formation and growth of the spark to ignite the mixture. The arrangement illustrated in Figs. 9-11 thus better assures ignition of the mixture and less chance of misfire, and also lowers the magnitude of the voltage pulse Vg required to produce the spark for igniting the mixture.

[0029] Preferably, voltage pulses V_aux should be from 2 to 7 kV; and the voltage pulses Vg should be from 15 to 25 kV, and applied about 2 to 40 microseconds after Vg. Good results were obtained when V_aux was 4 kV, and Vg was 18 kV and was applied about 10 microseconds after V_aux.

[0030] The spark plug illustrated in Fig. 12, therein generally designated 52, includes a high-voltage electrode 54 having a main section 54a axially aligned with the ground electrode 56 but axially spaced from it to define the air gap 57. The high-voltage electrode 54 further includes an auxiliary section 54b joined to and extending laterally of the main section 54a. The auxiliary section 54b includes a bent-over, pointed tip 54c spaced laterally of the air gap 57.

[0031] The high-voltage electrode 54 and ground electrode 56 are connected across a voltage source 58 which applies high-voltage pulses (Vg) producing the sparks in the air gap 57 to ignite the combustible mixture therein. The two electrodes 54, 56 are also energized by a source 59 of voltage Vor which supplies, via a diode D₁, constant current to the two electrodes 54, 56.

[0032] Thus, as described above, the magnitude of the current supplied by the voltage source 59 is sufficient to produce a corona discharge from the high-voltage electrode 54 particularly from its bent-over pointed tip 54c. This produces a "corona wind" which flows through the air gap 57, and thereby directs the ignited mixture, or spark kernel, away from the two electrodes 54, 56. As described above, the effect is to reduce the residence time of the spark kernel near both of the electrodes, and thereby to reduce the heat loss from the spark kernel by heat transfer to the electrodes. This result is to improve the ignition of the combustible mixture, to lower the HC emission, and to reduce fuel consumption.

[0033] Fig. 13 illustrates a spark plug, generally designated 62, of substantially the same construction as described above, except that the auxiliary electrode section 64b of the high-voltage electrode 64 is connected to the main section 64a via an electrical resistor R₁ having a high electrical resistance. Preferably, resistor R₁ is a ceramic semi-conductor having a resistance value of at least one megohm, e.g., about ten megohms. The arrangement illustrated in Fig. 2 also includes a high-voltage source 68, a constant current source 69, and a diode D₂, which function generally in the same manner as the corresponding elements 58, 59 and D₁ in the Fig. 12 arrangement, except that the electrical resistor R1, in the Fig. 13 arrangement, interrupts the constant current produced by voltage source 59 when the spark is applied by voltage source 58.

[0034] It will be appreciated that the voltage source supplying the constant current (e.g., source 59 in Fig. 12, source 69 in Fig. 13, or the corresponding sources in the embodiments described earlier) can be provided by a separate circuit added to an existing ignition system for internal combustion engines, thereby permitting such systems to be converted to one exploiting the spark-enhancing features of the invention. Alternatively, such a voltage source for supplying the constant current may be integrated into the design of the ignition system supplying the high voltage pulses. The features of the invention can also be implemented by using a preprogrammable power supply to produce the desired outputs to the spark plug electrodes.

Claims

1. Spark plug apparatus for an internal combustion engine, comprising: an electrode system including a high-voltage electrode and a ground electrode spaced therefrom to define an air gap into which a combustible mixture is to be introduced; and a high-voltage source for applying, during time-spaced intervals, high-voltage pulses between said high- voltage and ground electrodes to produce sparks in said air gap to ignite the combustible mixture therein; characterized in that said apparatus further includes spark-enhancing means operative during the time between sparks to create spark-enhancing conditions for the sparks when produced by said electrodes.

2. The apparatus according to Claim 1, wherein said spark-enhancing means comprises means for producing a corona wind in said air gap to direct the ignited mixture away from both said electrodes in order to reduce heat loss from the ignited mixture by heat transfer to said electrodes.

3. The apparatus according to Claim 3, wherein said means for producing a corona wind in said air gap comprises an auxiliary voltage souce supplying constant current continuously to said electrode system to produce a corona discharge therefrom in said air gap.

4. The apparatus according to either of Claims 2 or 3, wherein said electrode system includes only said high-voltage and ground electrodes.

5. The apparatus according to either of Claims 2 or 3, wherein said electrode system includes an auxiliary electrode, said auxiliary voltage source continuously applying constant current to said auxiliary and ground electrodes.

6. The apparatus according to any one of Claims 2-5, wherein said ground electrode is of cylindrical configuration and encloses said high-voltage electrode, said cylindrical ground electrode being formed with a plurality of windows on its circumference aligned with said air gap.

7. The apparatus according to any one of Claims 2-6, wherein both said high-voltage and ground electrodes are formed with parallel, spaced, end sections defining said air gap therebetween.

8. The apparatus according to Claim 5, wherein said auxiliary electrode includes a pointed tip adjacent said air gap between the high-voltage and ground electrodes.

9. The apparatus according to Claim 8, wherein said auxiliary electrode includes two end sections on opposite sides of the air gap between said high-voltage and ground electrodes.

10. The apparatus according to Claim 1, wherein said electrode system further includes an auxiliary electrode adjacent to said air gap, and said spark-enhancing means comprises an auxiliary voltage source for applying, just prior to the application of the high-voltage pulse between the high-voltage and ground electrodes, an auxiliary voltage pulse between said auxiliary and ground electrodes of sufficient magnitude to produce a plasma cloud in said air gap enhancing the production of a spark therein when the high-voltage pulse is applied between the high-voltage and ground electrodes.

11. The apparatus according to Claim 1, wherein said spark-enhancing means comprises means for applying continuous current between said electrodes at least during the intervals between said sparks.

12. The apparatus according to Claim 1, wherein said spark-enhancing means comprises means for applying auxiliary voltage pulses between said electrodes just prior to the application of said high-voltage pulses to said electrodes.

Drawing