Electrical transmission or interconnection systems – Vehicle mounted systems – Automobile
Reexamination Certificate
1999-11-08
2003-09-09
Toatley, Jr., Gregory J. (Department: 2836)
Electrical transmission or interconnection systems
Vehicle mounted systems
Automobile
C313S141000
Reexamination Certificate
active
06617706
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ignition system used for an igniter of an internal combustion engines, and particularly relates to an ignition system using a spark plug that can be effectively spark cleaned to have high resistance to fouling.
2. Description of the Related Art
In a parallel electrode type spark plug in which the distal end face of a central electrode opposes to a ground electrode, the voltage required is lower at the negative polarity than at the positive polarity and, hence, this type of spark plugs have been commonly used with an ignition system of negative polarity that applies a negative, high voltage to the central electrode. Accordingly, even in a semi-creep discharge type or an intermittent semi-creep discharge type of spark plugs that have a plurality of side ground electrodes provided to face the peripheral side of the central electrode, they are often used with the ignition system of negative polarity.
On the other hand, the internal combustion engine having high power and high performance, particularly the internal combustion engine for a motor cycle, has problems of breakage of the ground electrode due to mechanical vibration and excess heat of the ground electrode. It is difficult to apply the parallel electrode type spark plug to such an internal combustion engine. Further, the spark plug generally used has the main metallic shell having a small screw diameter such as M10S or M8S (JIS B8031) that is smaller than M14S. In this case, due to the size restriction of the main metallic shell, the cross sectional area of the ground electrode should be small. Consequently, the large amount of projection of the ground electrode like the parallel electrode type spark plug is difficult. Therefore, in such an internal combustion engine, a multi-electrode type spark plug in which a plurality of ground electrodes are provided so that they oppose to the peripheral side of the central electrode. In the multi-electrode type spark plug, if the ignition system in the negative polarity, it becomes a serious problem that the wearing of the central electrode which is collided with positive ions having heavy mass.
Further, since a problem of a carbon fouling during low load may easily occur, a semi-creep discharge type or an intermittent semi-creep discharge type of spark plugs have been used, in which a plurality of ground electrodes are provided to oppose to the peripheral side of the central electrode, and spark runs on the surface of the porcelain insulator between the central electrode and the ground electrode. In such a creepage spark discharge type spark plug, so-called “creepage spark discharge” occurs, in which spark runs on the surface of the porcelain insulator. Accordingly, the channeling problem on the surface of the porcelain insulator easily occur. If the channeling proceeds, the heat resistance and the reliability of the spark plug are lowered to thereby shorten the life of the spark plug.
Generally, if the diameter of the central electrode is made small, the discharge voltage is lowered to thereby improve the ignitability. However, particularly, if the diameter of the central electrode of the spark plug is small which is used for the negative ignition system, the electrode is rapidly worn and the ground electrode is partially worn. Accordingly, the life of the spark plug is shortened and it can not be used for practical use.
SUMMARY OF THE INVENTION
The present inventors found that if a specific spark plug is used, the channeling resistance of the ignition system in positive polarity in which positive voltage is applied to the central electrode is superior in comparison with the general ignition system in negative polarity.
It is an object of the present invention to provide an ignition system used for high-power and high-performance internal combustion engines, capable of preventing the breakage and the excessive heating of the spark plug used therein, the system having excellent ignitability, high durability and long life. Further, it is another object of the present invention to provide an ignition system in which the fouling resistivity and ignitability of the spark plug used therein, and it is strong against the channeling to thereby elongate its life.
According to the first aspect of the present invention, an ignition system comprises: a spark plug comprising a central electrode, an porcelain insulator for holding the central electrode, a main metallic shell for holding the porcelain insulator, and a ground electrode electrically connected to the main metallic shell; and a positive voltage applying unit for applying a positive voltage to the central electrode of the spark plug in comparison with the ground electrode, so that an ignition high voltage is applied between the central electrode and the ground electrode; wherein a spark discharge gap is formed between the ground electrode and a distal end portion of the central electrode; and the ground electrode is positioned so that a rear edge of a mating face opposed to a peripheral side of the central electrode is positioned in the side of the distal end of the central electrode in comparison with an end face of the porcelain insulator.
In this ignition system, wherein the positive voltage applying unit may comprise an ignition coil having a primary coil and a secondary coil, and a primary current flowing in the primary coil of the ignition coil is stopped at a predetermined ignition period so as to apply the ignition high voltage is applied between the central electrode and the ground electrode of the spark plug. Further, in this ignition system, the positive voltage applying unit may further comprise a electric power source connected to the primary coil of the ignition coil and a control unit for controlling the ignition period of the primary current.
With this design, more of the spark jumps that are created by application of high voltage occur anywhere but along the surface of the porcelain insulator. In particular, according to an experiment on spark plugs that were operated with positive high voltage being applied to the central electrode, an appreciably increased proportion of the spark jumps occurred at the tip of the central electrode which was distant from the surface of the porcelain insulator. This enabled the spark plugs to be fired efficiently. What is more, the proportion of spark jumps along the surface of the porcelain insulator decreased dramatically during normal service and the chance of the spark of damaging the surface of the porcelain insulator is correspondingly reduced to make the spark plugs more resistant to channeling.
FIGS. 24 and 25
are section views of the distal end portion of a spark plug, showing how individual parts of the spark plug are electrified.
FIG. 24
refers to the case of the present invention in which positive high voltage is applied to central electrode
2
, and
FIG. 25
refers to the conventional case where negative high voltage is applied to central electrode
2
.
First, in the case of the present invention where central electrode
2
has positive polarity, the surface of porcelain insulator
1
, particularly its end face, becomes negatively charged by dielectric polarization (see FIG.
24
). As a result, the electric field near the front edge
11
A of ground electrode
11
becomes stronger than the electric field near the rear edge
11
B and spark is produced from the front edge
11
A more frequently than from the rear edge
11
B. However, the spark frequently produced at the front edge
11
A is so much distant from the porcelain insulator
1
that channeling and other unwanted phenomena are less likely to occur.
Secondly, even if spark is produced at the rear edge
11
B of the ground electrode
11
, the negatively charged particles (e.g., electrons) that make up the greater part of the spark are repelled by the negative charge on the surface of the porcelain insulator
1
and the spark is more to prone to flash at a distance from the porcelain insulator
1
due to electrostatic repulsion.
Ito Shoichiro
Iwata Kazuya
Kokubu Akio
Matsubara Yoshihiro
Ono Hiroshi
NGK Spark Plug Co. Ltd.
Toatley , Jr. Gregory J.
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