Spark plug for internal combustion engine

Abstract

A spark plug for an internal combustion engine is disclosed having a metal shell having an outer periphery formed with a mounting thread, a porcelain insulator fixedly secured to the metal shell on a central axis thereof, a center electrode retained within the porcelain insulator along a central axis thereof with a distal end located outside the porcelain insulator, and a ground electrode joined to the metal shell and having an end associated with the distal end of the center electrode to define therebetween a spark discharge gap. The ground electrode includes a facing surface intersecting the central axis of the center electrode and having a width equal to or less than 1.6 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show how the same may be carried into effect, there will now be described by way of example only, specific embodiments according to the present invention with reference to the accompanying drawings, in which:

FIG. 1 is a partially cross sectional view showing a spark plug of a first embodiment according to the present invention;

FIG. 2 is an enlarged side view showing a vicinity of an igniting area of the spark plug shown in FIG. 1;

FIG. 3 is an enlarged front view showing the vicinity of the igniting area of the spark plug shown in FIG. 1;

FIG. 4 is an enlarged front view showing a vicinity of an igniting area of a spark plug of a second embodiment according to the present invention;

FIG. 5 is an enlarged side view showing a vicinity of an igniting area of the spark plug shown in FIG. 4;

FIG. 6 is an enlarged front view showing a vicinity of an igniting area of a spark plug of a third embodiment according to the present invention;

FIG. 7 is an enlarged side view showing the vicinity of the igniting area of the spark plug shown in FIG. 6;

FIG. 8 is a cross sectional view showing a ground electrode forming a part of a spark plug of a fourth embodiment according to the present invention;

FIG. 9 is a cross sectional view showing a modified form of the ground electrode forming the part of the spark plug of the fourth embodiment according to the present invention;

FIG. 10 is a cross sectional view showing another modified form of the ground electrode forming the part of the spark plug of the fourth embodiment according to the present invention;

FIG. 11 is a cross sectional view showing still another modified form of the ground electrode forming the part of the spark plug of the fourth embodiment according to the present invention;

FIG. 12 is a graph showing the relationship between a width of a facing surface of the ground electrode and an incidence rate of a fuel clamping rate or a fuel bridging rate caused in a spark plug of a fifth embodiment according to the present invention;

FIG. 13 is a graph showing the relationship between an axial length of a noble metal chip joined to the ground electrode and a related ignitability of a spark plug of a sixth embodiment according to the present invention;

FIG. 14 is a graph showing the relationship an axial length of a noble metal chip joined to the ground electrode and an incidence rate of a fuel clamping rate or a fuel bridging rate caused in a spark plug of a seventh embodiment according to the present invention;

FIG. 15 is a cross sectional view showing a center electrode and a ground electrode forming parts of a spark plug of an eighth embodiment according to the present invention; and

FIG. 16 is a graph showing the relationship between a width of a facing surface of a ground electrode and an increasing ratio of a spark discharge gap.

Claims

1. A spark plug for an internal combustion engine, comprising: a metal shell having an outer periphery formed with a mounting thread;a porcelain insulator fixedly secured to the metal shell on a central axis thereof;a center electrode retained within the porcelain insulator along a central axis thereof with a distal end located outside the porcelain insulator; anda ground electrode joined to the metal shell and having an end associated with the distal end of the center electrode to define therebetween a spark discharge gap;wherein the ground electrode includes a facing surface intersecting the central axis of the center electrode and having a width equal to or less than 1.6 mm.

2. The spark plug according to claim 1, wherein: the ground electrode has a maximum width in cross section, involving the facing surface, which is greater than the width of the facing surface.

3. The spark plug according to claim 1, wherein: the ground electrode has sidewalls whose corners are formed with chamfered portions, respectively.

4. The spark plug according to claim 1, wherein: the ground electrode includes a noble metal chip supported on the facing surface so as to protrude into the spark discharge gap.

5. The spark plug according to claim 1, wherein: the facing surface of the ground electrode has the width equal to or greater than 0.6 mm.

6. The spark plug according to claim 1, wherein: the ground electrode includes a noble metal chip, supported on the facing surface so as to protrude into the spark discharge gap; andthe distal end of the center electrode is directly exposed to the spark discharge gap in face-to-face relationship with the facing surface of the ground electrode.

7. The spark plug according to claim 1, wherein: the noble metal chip has an outer diameter falling in a range equal to or greater than 0.4 and equal to or less than 1.0 mm.

8. The spark plug according to claim 1, wherein: the noble metal chip has an axial length falling in a range equal to or greater than 0.3 and equal to or less than 1.5 mm.

9. The spark plug according to claim 1, wherein: the distal end of the center electrode has an outer diameter falling in a range equal to or greater than 2 mm.

10. The spark plug according to claim 1, wherein: the ground electrode has a maximum width in cross section, involving the facing surface, which is greater than the width of the facing surface;the ground electrode has sidewalls whose corners are formed with chamfered portions, respectively; andthe ground electrode includes a noble metal chip supported on the facing surface so as to protrude into the spark discharge gap.

11. The spark plug according to claim 10, wherein: the noble metal chip has an outer diameter falling in a range equal to or greater than 0.4 and equal to or less than 1.0 mm.

12. The spark plug according to claim 10, wherein: the noble metal chip has an axial length falling in a range equal to or greater than 0.3 and equal to or less than 1.5 mm.

13. The spark plug according to claim 1, wherein: the ground electrode has a maximum width in cross section, involving the facing surface, which is greater than the width of the facing surface;the ground electrode has sidewalls whose corners are formed with chamfered portions, respectively; andthe distal end of the center electrode is directly exposed to the spark discharge gap in face-to-face relationship with the facing surface of the ground electrode.

14. The spark plug according to claim 1, wherein: the ground electrode has a maximum width in cross section, involving the facing surface, which is greater than the width of the facing surface; andthe ground electrode includes a noble metal chip supported on the facing surface so as to protrude into the spark discharge gap.

15. The spark plug according to claim 14, wherein: the noble metal chip has an outer diameter falling in a range equal to or greater than 0.4 and equal to or less than 1.0 mm.

16. The spark plug according to claim 14, wherein: the noble metal chip has an axial length falling in a range equal to or greater than 0.3 and equal to or less than 1.5 mm.

17. The spark plug according to claim 1, wherein: the ground electrode has a maximum width in cross section, involving the facing surface, which is greater than the width of the facing surface; andthe ground electrode has sidewalls whose corners are formed with circular arc shaped chamfered portions, respectively.

18. The spark plug according to claim 1, wherein: the ground electrode has a maximum width in cross section, involving the facing surface, which is greater than the width of the facing surface; andthe ground electrode has sidewalls formed in circular arc shaped configurations, respectively.

19. The spark plug according to claim 1, wherein: the ground electrode has a maximum width in cross section, involving the facing surface, which is greater than the width of the facing surface; andthe ground electrode has sidewalls formed in tapered configurations, respectively, with respect to the facing surface.

20. The spark plug according to claim 1, wherein: the ground electrode has a maximum width in cross section, involving the facing surface, which is greater than the width of the facing surface; andthe ground electrode has sidewalls formed in inwardly dent configurations, respectively.