Multi-gap spark ignition system

Abstract

A multi-gap spark ignition system is disclosed. The system comprises a plurality of spark gaps which are formed in series. The length of the spark gaps increases from the high voltage power source side towards the earth side. According to the present invention, necessary voltage to be applied to the spark ignition system can be decreased.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a multi-gap spark ignition system to be installed in a spark-ignition engine.

Recently, lean-burn systems, exhaust gas recirculation systems or the like have been adopted in order to reduce harmful components in the exhaust gases of an automobile and in order to prevent the waste of resources.

However, according to these systems, the ignitability and the combustion speed are lower.

Conventionally, the ignitability and the combustion speed have been improved by providing a plurality of ignitors.

However, in this case, the number of high voltage power sources also increases.

In order to decrease the number of the high voltage power sources, a system wherein a plurality of spark gaps having a constant width are formed in series has been proposed.

However, as the number of the spark gasp increases, necessary voltage to be applied thereto increases.

Accordingly, one object of the present invention is to provide a multi-gap spark ignition system which is effective for improving the ignitability of an engine.

Another object of the present invention is to provide a multi-gap spark ignition system of which the necessary voltage can be reduced as compared with the conventional system of the same type.

DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent from the following description of embodiments thereof with reference to the accompanying drawings wherein:

FIG. 1 is a plan view of a first embodiment of the multi-gap spark ignition system according to the present invention;

FIG. 2 is a plan view of a second embodiment of the multi-gap spark ignition system according to the present invention; and

FIGS. 3 to 5 are graphs showing the experimental results of the relation between the necessary voltage of the spark ignition systems and the inner pressure of the cylinder.

SUMMARY OF THE INVENTION

In the multi-gap spark ignition system according to the present invention, a plurality of spark gaps are formed in series so that the length of the spark gaps increases from the high voltage power source side towards the earth side. According to the present invention, the necessary voltage to be applied to the spark ignition system can be decreased as compared with the conventional system of which each spark gap has a constant length substantially equal to the average length of the spark gaps of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be explained in detail in accordance with embodiments and experiments thereof.

FIG. 1 illustrates a first embodiment of the multi-gap spark ignition system according to the present invention.

In FIG. 1, an insulating plate 1 formed of alumina ceramics having a thickness of about 6 mm is interposed between a cylinder head (not shown) and a cylinder block (not shown) of an internal combustion engine of an automobile through gaskets (not shown). The insulating plate 1 is provided with a central hole which defines one portion of the combustion chamber 6 of the engine.

A high voltage electrode 2a, intermediate electrodes 2b, 2c and an earth electrode 2d, are formed of nickel alloy so as to have a diameter of 2.5 mm and are buried within the insulating plate 1.

One end of each of the electrodes 2a, 2b projects from the insulating plate 1 into the combustion chamber 6 so as to be opposed to each other. Between the projecting ends of the electrodes 2a, 2b, a spark gap 3a is formed. One end of each of the electrodes 2c, 2d also projects into the combustion chamber 6 so as to be opposed to each other. Between the projecting ends of the electrodes 2c, 2d, a spark gap 3b is formed in symmetry with the spark gap 3a in the radial direction of the central hole of the insulating plate 1. The projecting end of each of the electrodes 2a, 2b, 2c and 2d preferably is in the shape of the letter L.

The other end of the electrode 2a is connected to a secondary ignition coil 5 through a terminal 4a. The other end of the electrode 2d is connected to a terminal 4b which is earthed.

The electrodes 2b, 2c are integrally connected to each other within the insulating plate 1.

The length of the spark gap 3b on the earth side is made larger than that of the spark gap 3a on the high voltage power source side.

For example, the length of the spark gap 3a is 0.3 mm and the length of the spark gap 3b is 0.5 mm.

When high voltage is applied between the terminals 4a 4b by means of the ignition coil 5, breakdown firstly occurs in the spark gap 3a having a length of 0.3 mm so that an electric current flows therethrough. As a result, potential difference between the electrodes 2a, 2b disappears.

Then, through the spark gap 3b having a length of 0.5 mm, breakdown occurs.

FIG. 2 illustrates a second embodiment of the multi-gap spark ignition system.

In the second embodiment, four spark gaps are formed in series at regular intervals.

In FIG. 2, the reference numeral 2a designates a high voltage electrode, 2b, 2c, 2d, 2e, 2f, 2g, designate intermediate electrodes and 2h designates an earth electrode and the reference numerals 3a, 3b, 3c, 3d designate spark gaps.

For example, the length of the spark gap 3a is 0.25 mm, the length of the spark gap 3b is 0.35 mm, the length of the spark gap 3b is 0.45 mm and the length of the spark gap 3d is 0.55 mm.

The average length of the spark gaps 3a, 3b, 3c, 3d is 0.4 mm.

According to the second embodiment, necessary voltage to be applied to the spark ignition system can be made small as compared with the conventional spark ignition system provided with four spark gaps having an equal length of 0.4 mm.

Hereinafter, the results; of the experiments made by the inventors will be explained.

FIG. 3 shows the relation between the inner pressure of the cylinder and the necessary voltage to be applied to the ignition systems provided with the different number of spark gaps.

The length of all spark gaps is 0.4 mm.

In FIG. 3, the lines A, B, C, D show the results of the spark ignition systems provided with one, two, three, and four spark gaps, respectively.

As is apparent from the experimental result, as the number of spark gaps increases, necessary voltage to be applied to the spark ignition system increases.

FIG. 4 shows the experimental result of the spark ignition systems provided with two spark gaps. The line E shows the result of the spark ignition system according to the first embodiment of the present invention, which is provided with two spark gaps having a length of 0.3 mm and 0.5 mm, the line B shows the result of the spark ignition system of which all spark gaps have a length of 0.4 mm, and the line F shows the result of the spark ignition system of which spark gap on the high voltage power source side has a length of 0.5 mm and that on the earth side has a length of 0.3 mm.

As is apparent from the experimental result of FIG. 4, necessary voltage of the ignition system of the present invention (line E) is smaller than that of the other ignition systems (lines B and F).

FIG. 5 shows the experimental result of the ignition systems provided with four spark gaps, respectively. The line H shows the result of the ignition system according to the second embodiment of the present invention, of which spark gaps have a length of 0.25 mm, 0.35 mm, 0.45 mm, and 0.55 mm, respectively, the line D shows the result of the ignition system of which all spark gaps have an equal length of 0.4 mm and the line G shows the result of the ignition system wherein spark gaps having a length of 0.55 mm, 0.45 mm, 0.35 mm and 0.25 mm are arranged from the high voltage power source side towards the earth side in this order.

As is apparent from FIG. 5, necessary voltage of the spark ignition system of the present invention (line H) is smaller than that of the spark ignition system of which spark gaps has an equal length (line D). And the necessary voltage of the spark ignition system provided with spark gaps of which length gradually decreases from the high voltage power source side towards the earth side (line G) is much larger than that of the spark ignition system provided with spark gaps of which length is equal.

As described above, the present invention relates to a multi-gap spark ignition system provided with a plurality of spark gaps which are formed in series. And the present invention is characterized in that the length of the spark gaps is gradually increased from the high voltage power source side towards the earth side.

According to the present invention, necessary voltage can be decreased as compared with the conventional spark ignition system of which spark gaps have an equal length to one another.

The multi-gap spark ignition system of the present invention can be applied to the ignition system employing a screw type spark plug provided with two electrodes which are opposed to each other through a predetermined spark gap so as to be electrically insulated from each other.

Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the invention as set forth herein.

Claims

1. A multi-gap spark ignition system to be installed in an internal combustion engine for igniting air-fuel mixture introduced therein, comprising:

a plurality of electrodes which are adapted to be installed in the wall defining a combustion chamber of the engine to form at least three spark gaps therebetween exposed to the chamber;

a high voltage power source which supplies an electric current to said plurality of electrodes for generating breakdown in said spark gaps;

said electrodes being composed of a high voltage electrode which is connected to said high voltage power source, an earth electrode which is earthed, and a plurality of intermediate electrodes which are positioned between said high voltage electrode and said earth electrode;

said electrodes projecting into said combustion chamber to form said spark gaps between two projecting ends of adjacent two electrodes with said electrodes being arranged in series through said spark gaps and said projecting ends being in the shape of the Letter L with said ends of adjacent electrodes being opposed;

said electrodes being buried within an insulating plate which is adapted to be interposed between a cylinder block and a cylinder head of the internal combustion engine;

said insulating plate being provided with a central hole to define one portion of the combustion chamber with one end of each electrode projecting into said hole; and

the length of said spark gaps gradually increasing from the high voltage power source side towards the earth side.