GB2149852A

GB2149852A - Spark plugs

Info

Publication number: GB2149852A
Application number: GB08429085A
Authority: GB
Inventors: Richard Walter Anderson; Joseph Richard Asik; Richard Carl Ronzi
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1983-11-18
Filing date: 1984-11-16
Publication date: 1985-06-19
Also published as: JPS60121692A; GB8429085D0; GB2149852B; DE3441997A1; BR8405685A

Abstract

The spark plug comprises a first ring-shaped electrode 12 surrounding a second electrode 11 and an insulator 13 positioned between the electrodes to provide a surface for a spark path, the insulator being spaced from the first electrode to provide an air gap 14. The spark plug has a high inherent capacitance and generates a plasma shock wave which produces a large initial flame kernal. The plug may be used in a distributorless ignition system which has low generated radio frequency interference. <IMAGE>

Description

SPECIFICATION Blast gap ignition system BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to spark plugs for use in internal combustion engines.

2. Prior Art U.S. Patent 3,202,859 issued to Knaggs teaches a spark plug in which a central electrode extends above the end of the spark plug. The elongated central electrode is surrounded by an insulator which is, in turn, surrounded by the ground electrode. The ground electrode is an annular shell which is in direct contact with the insulator. There is no air gap in this construction and the spark generated travels along the surface of the insulator from the central electrode to the ground electrode.

U.S. Patent 4,087,719 issued to Pratt, Jr.

teaches a spark plug with an insulator between an annular ground electrode and a central live electrode. The central electrode has a sparking surface which is not covered by the insulator. The annular ground electrode is attached to the spark plug body. The annular electrode and the central insulator are not in direct contact with any air gap.

U.S. Patent 3,683,232 issued to Baur teaches a spark plug cap wherein a capacitance is connected between a live electrode lead and ground. The extra capacitance functions to increase the intensity of the spark generated at an air gap between the live electrode and the ground electrode.

Further improved ignition is desired in engines using a lean air to fuel ratio. In particular, it would be desirable to produce in high swirl engines a stable discharge with both greatly increased arc length and ionization volume without significantly higher required breakdown voltage, thus leading to improved ignitablity. These are some of the problems this invention overcomes.

SUMMARY OF THE INVENTION In accordance with this invention, a spark plug has a ring air gap and surface spark path between a first electrode and a second electrode. The first electrode has a ring shape and defines a central opening. The second electrode is positioned within the central opening of the first electrode. A ceramic insulating material is positioned between the first and second electrodes so as to provide a surface for a spark path between the first and second electrodes. The insulating material is spaced from the first electrode ring so as to provide therebetween an air gap. As a result, the spark path follows the insulating material surface until the air gap to the first electrode is reached where the spark leaves the surface of the insulating material.

This invention provides improved sparking which is especially advantageous for igniting high swirl or high in-cylinder flow mixtures.

The advantage occurs because the spark, once ignited anywhere along the ring electrode, can move along the ring electrode and ceramic surface to a region of low flow velocity on the sheltered side of the spark plug opposite from the side impinged by gas flow.

This helps to maintain the flame kernel attached to the ring electrode, leads to improved ignitability and reduces cycle by cycle combustion pressure variation. The initial flame kernel has a more favorable region to develop on the lee side of the ceramic tip of the plug than on the high velocity side, since the lower velocities present on the lee side reduce the convective heat loss from the developing nascent flame kernel. This allows more rapid flame kernel development and a more consistant ignition location for improved combustion stability. Including an air gap spark path, in addition to the surfaces spark path, facilitates spark movement and insures sparking even if the surface becomes fouled with carbon.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of the tip of a spark plug in accordance with an embodiment of this invention; Fig. 2A is a cross section view of a spark plug in accordance with an embodiment of this invention; Fig. 2B is a portion of a view similar to Fig.

2A wherein one spark plug electrode is toroidal with a circular cross section; and Fig. 3 is a circuit diagram suitable for connection to a spark plug in accordance with an embodiment of this invention.

DETAILED DESCRIPTION OF THE INVEN TION Referring to Fig. 1, a spark plug 10 includes a central electrode 11 and an annular ring electrode 1 2. Concentric about electrode 11 is a ceramic insulator 1 3 with a generally tubular shape. Electrode 11 is generally elongated with a right cylindrical shape having a diameter of 1 to 3 mm, typically. Insulator 1 3 is concentric about electrode 11 and in contact with electrode 11. Electrode 1 2 is formed in a ring (12 in Fig. 2A) or toroidal washer (1 2B in Fig. 2B) shape about insulator 1 3 and is spaced from insulator 1 3 by a ring like air gap 14 having a dimension of about 0.25 to 0.75 mm, typically.The outside diameter of the ring is about 8-1 2 mm, while its inside diameter is about 4-6 mm, typically.

In operation, a spark path, S, tracks the surface of insulator 1 3 from electrode 11 until air gap 14 is reached where the spark path jumps air gap 14 to electrode 1 2. As a result, most of the breakdown voltage (10-30 KV, typically) required during actual engine operation is to breakdown air gap 14 while the length of the spark can be substantially longer than air gap 14, since it includes the track over the surface of insulator 13. The length of surface tracking is about 1 to 3 mm, typically.

Referring to Fig. 2A, a cross section of spark plug 10 includes an integral capacitor 1 5 which is formed from a conductive member 1 6 which is coupled to electrode 12, a dielectric member 1 7 and a conductive member 18 receiving spark energy coupled to spark plug 10. Conductive member 18 is electrically connected to electrode 11. Dielectric member 1 7 is generally tubular and extends axially along a portion of spark plug 10.

In order to maintain a stable, non-extinguishable sparking arc during high in-cylinder flow conditions, the ring gap plug requires sufficient ignition energy. Further, the added plug capacitance requires extra ignition energy to satisfactorily charge up the capacitance to a spark plug breakdown voltage. Fig.

3 shows a circuit which provides sufficient ignition energy for the operation of a ring gap spark plug in accordance with an embodiment of this invention.

Referring to Fig. 3, showing a high energy four cylinder distributorless ignition system, a typical connection is shown including coils 20, 21, 22 and 23 coupled to an ignition module 24 which is controlled by an engine control computer 26. Capacitors 28, 29, 30 and 31 are shown in parallel with spark plug gaps 32, 33, 34 and 35, respectively. Coils 20 and 22 are coupled to spark plug gaps 32, 33, 34 and 35 by diodes 36, 37, 38 and 39, respectively. Coils 21 and 23 are coupled to spark plug gaps 32, 33, 34 and 35 by diodes 40, 41, 42 and 43, respectively.

In operation, by analyzing input sensor signals from the engine (not shown) and following an internal control program, the electronic engine control module determines when to energize and de-energize a pair of coils, e.g.

20 and 21. The time interval of energization is commonly called dwell and the de-energizing time is called the spark timing. Sufficient dwell time is allowed to ensure adequate stored energy in the coils. Upon de-energizing, energy is quickly transferred from each coil primary winding to the coil secondary winding, resulting in secondary current flow into each capacitor, 28 and 29, until spark gap breakdown occurs. Upon breakdown, the energy residing on the capacitors and any residual coil energy are discharged into gaps 32 and 33. One gap, e.g. 32, corresponds to an engine cylinder in the compression stroke, while the other, 33, corresponds to an engine cylinder in the exhaust stroke.The high voltage diodes 36 and 40 "OR" two negative voltage outputs into plug gap 32, while diodes 41 and 37 "OR" two positive voltage outputs into plug gap 33. The ignition module includes power transistor switches used to energize and de-energize the coil primary windings from a 14 V battery supply. Similar events occur 180 of crank angle later when the lower pair of coils 22 and 23, gaps 34 and 35, diodes 38, 39, 42 and 43, are activated by the electronic engine control module.

Advantageously, spark plug 10 has a higher plug capacitance (100-200 picofarads) versus a currently common value of about 10 picofarads. This leads to much increased peak capacitance current of 200 to 1000 amperes vs. 10-50 amperes in the initial breakdown event which occurs during the first 100 nanoseconds of spark generation. Such an intense and rapid initial breakdown generates a plasma shock wave which produces a much larger initial flame kernel, leading to a 0-10% mass fraction burn time reduction up to about 10%, and improved ignitability and combustion stability. The large circumferential ground electrode and the plug have a structure providing good durability and heat range capability.

The use of a distributorless ignition system by itself with this spark plug provides engine packaging flexibility, low generated radio frequency interference and improved reliability.

The combination of the ring gap spark plug with a distributorless system and additional capacitance in parallel with the spark gap can provide benefits such as extended lean operation with improved fuel economy, improved combustion stability resulting in better driveablity, reduced radio frequency interference through elimination of the distributor, reduced complexity, improved idle quality and reduced idle fuel flow, and improved wet weather starting because of lack of condensation in distributor.

Various modifications and variations will no doubt occur to those skilled in the arts to which this invention pertains. For example, the particular cross-sectional configuration of the ring electrode may be varied from that disclosed herein. Moreover, capacitance can be added to the plug using an external adapter which is part of the plug boot. These and all other variations which basically rely on the teachings through which this disclosure has advanced the art are properly considered within the scope of this invention, as set forth in the appended claims.

Claims

1. A spark plug having a ring air gap and surface spark path including: a first electrode having a ring shape defin ing a central opening; a second electrode positioned within said central opening of said first electrode; and an insulating material positioned between said first and second electrodes so as to provide a surface for a spark path between said first and second electrodes, said insulating material being spaced from said first elec trode so as to provide therebetween an air gap.

2. A spark plug as recited in claim 1 wherein said insulating material is of a ceramic material and extends axially beyond the plane of the ring of said first electrode, and said second electrode extends beyond the axial extent of said ceramic insulating material.

3. A spark plug as recited in claim 2 further comprising a capacitance in parallel with said spark path between said first and second electrodes.

4. A spark plug as recited in claim 3, wherein: said first electrode has a generally circular shape with a generally rectangular cross sec tion.

5. A spark plug as recited in claim 3, wherein: said first electrode has a generally circular cross section.

6. A spark plug as recited in claim 3, wherein: said second electrode and said insulating material are adjacent each other and at least portions of which are in contact with each other; and said capacitance having a first plate coupled to said first electrode, a second plate coupled to said second electrode, and a dielectric member, intermediate said first and second plates, having a generally tubular shape extending axially along at least a portion of the length of said spark plug.

7. A spark plug as recited in claim 6, wherein: said air gap has an extent of about 0.25 to 0.75 mm, said first electrode has an outside diameter of about 8 to 1 2 mm and an inside diameter of about 4 to 6 mm, and said insulating material having a tracking surface of about 1 to 3 mm between said second electrode and said air gap adapted for supporting a spark path.

8. An ignition system means including: a distributorless ignition system adapted to provide a relatively high ignition energy for firing a pair of spark plugs, each of said spark plugs having a plug capacitance of about 100 to 200 picofarads and an initial breakdown current of about 200 to 1000 amperes; and each of said spark plugs having: a first electrode having a ring shape defining a central opening; a second electrode positioned within said central opening of said first electrode; a ceramic insulating material positioned be- tween said first and second electrodes so as to provide a surface for a spark path between said first and second electrodes, said insulating material being spaced from said first electrode so as to provide therebetween an air gap; said insulating material extending axially beyond the plane of the ring of said first electrode, and said second electrode extending beyond the axial extent of said insulating material; said second electrode and said insulating material being adjacent each other and having at least.portions which are in contact with each other; ; a capacitance in parallel with said spark path between said first and second electrodes, said capacitance having a first plate coupled to said first electrode, a second plate coupled to said second electrode, and a dielectric member, intermediate said first and second plates, having a generally tubular shape extending axially along at least a portion of the length of said spark plug.

9. A spark plug having a ring air gap, constructed substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.