Electric lamp or space discharge component or device manufacturi – Process – Spark plug or spark gap making
Reexamination Certificate
2000-04-10
2002-01-01
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
Spark plug or spark gap making
Reexamination Certificate
active
06334800
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims the priority of Japanese Patent Applications No. H9-105490 filed on Apr. 23, 1997, H9-106975 filed on Apr. 24, 1997, H9-107141 filed on Apr. 24, 1997, H9-257542 filed on Sep. 5, 1997 and H9-362693 filed on Dec. 12, 1997, and Japanese Patent Application No. H10-104158 filed on Mar. 30, 1998 with the title of the invention of “Resistor-Incorporated Spark Plug, Resistor Composition for Spark Plug and Manufacturing Method of Resistor-Incorporated Spark Plug”, which are incorporated herein by reference.
The present invention relates to spark plugs to be used for internal combustion engines and, more particularly, to a spark plug into which a resistor for prevention of occurrence of radio frequency noise is incorporated and the manufacturing method thereof.
As this type of spark plug, there has conventionally been known one having a structure that a terminal is fixed in one end portion of a through hole formed along the axial direction of an insulator while a center electrode is similarly fixed in the other end portion of the through hole, where a resistor is placed between the terminal and the center electrode within the through hole. This resistor is implemented by one which is formed through steps of mixing amorphous carbon (e.g., carbon black) into glass powder and/or dielectric ceramic powder and thereafter sintering the mixture by hot press or the like as shown in Japanese Patent Laid-Open Publication S61-104580, S61-253786, or H2-126584.
In this connection, recently internal combustion engines such as automobile engines are on the trend toward higher output, while power supply ability has been on the increase for improvement of ignitionability. Also, with the downsizing of internal combustion engines, resistor-incorporated spark plugs have also been required to be smaller in size and higher in performance. Under these circumstances, there is an issue that when some high load is applied on such a resistor-incorporated spark plug, particularly on a small-size spark plug with a small-diameter resistor, the carbon that imparts electrical conductivity to the resistor would burn, causing the resistance value to increase, so that a stable load life characteristic could not be obtained.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a resistor-incorporated spark plug, as well as a manufacturing method therefor, which is enabled to offer a stable load life characteristic even when a high load is applied thereon, and also to provide a resistor composition to be used for the resistor-incorporated spark plug.
Resistor-incorporated spark plugs according to the present invention have the following common structure in their essential part. That is, with respect to a through hole formed along an axis of an insulator, a terminal is fixed to one end side of the through hole while a center electrode is fixed to the other end side of the through hole, and a resistor made of a resistor composition principally comprising a conductive material, glass particles and ceramic particles other than glass is placed between the terminal and the center electrode within the through hole. Further, in a first constitution of the resistor-incorporated spark plug of the present invention, the resistor composition contains, as the ceramic particles, semiconductive ceramic particles, and (&agr;
2
−&agr;
1
)/&agr;
1
≧−0.30 where a value of electric resistance measured by making conduction between the terminal and the center electrode via the resistor is &agr;
1
at 20° C. and &agr;
2
at 150° C.
In an attempt to improve the load life characteristic of the spark plug, proposals for stabilizing the load life of the resistor by blending TiO
2
particles, which is a semiconductor oxide, in the resistor have been disclosed, for example, in Japanese Patent Laid-Open Publications S58-102480, S58-102481, S58-189917, S59-17201, S59-17202, S60-150601, S60-150602 and Japanese Patent Publication H5-52641. However, with higher output of an internal combustion engine, the spark plug used as it is attached to the internal combustion engine may increase in temperature so that the resistor built in the spark plug also increases in temperature, for example, to as high as about 100-300° C. When such a state occurs, the electric resistance of the semiconductive TiO
2
, and moreover the specific electrical resistivity of the resistor, decreases so that the radio frequency noise prevention performance (radio frequency noise performance) is impaired, as a disadvantage.
Therefore, according to the first constitution of the invention, in the spark plug in which semiconductive ceramic particles are blended in the resistor, a condition of (&agr;
2
−&agr;
1
)/&agr;
1
≧−0.30 is satisfied, where the value of electric resistance measured by making conduction between the terminal and the center electrode via the resistor is &agr;
1
at 20° C. and &agr;
2
at 150° C. By this setting, enough radio frequency noise prevention performance can be obtained even at high temperatures. In addition, if (&agr;
2
−&agr;
1
)/&agr;
1
<−0.30, then the noise prevention performance at high temperatures may become insufficient. It is more preferable to satisfy that (&agr;
2
−&agr;
1
)/&agr;
1
≧−0.27.
Next, it is possible that the resistor composition contains, as the semiconductive ceramic particles, 0.5-20 weight % of TiO
2
particles whose mean particle size of a particle image obtained from observation of its cross-sectional structure falls within a range of 0.5-20 &mgr;m, the TiO
2
particles at least partly having a rutile type crystalline structure. It is noted that although every metal oxide herein is represented by a composition formula having a stoichiometric composition, there are some cases actually where the metal oxide becomes a nonstoichiometric composition due to oxygen deficiency.
With this constitution, a successful load life characteristic can be ensured even under a high load condition by 0.5-20 weight % of TiO
2
particles being contained in the resistor composition. Further, by adjusting the mean particle size of the TiO
2
particles to be blended in the resistor composition within a range of 0.5-20 &mgr;m so that the TiO
2
particles at least partly have a rutile type crystalline structure, high-temperature deterioration of the radio frequency noise prevention performance by the resistor can be effectively suppressed.
For example, when the resistor contains TiO
2
particles and a non-metallic conductive material such as carbon particles, its conduction path is formed by contact between non-metallic conductive material particles themselves, between non-metallic conductive material and TiO
2
particles or between TiO
2
particles themselves. Besides, it is considered that the electric resistance value of the resistor can be expressed by a sum of intrinsic resistance (bulk resistance) of these particles and contact resistance between the particles.
In this connection, as a result of the present inventors' energetic researches, it was found out that the temperature dependency of a resistor as described above is ruled mainly by temperature variation in the intrinsic resistances of the individual particles. Meanwhile, TiO
2
has been known to have three types of crystalline structures under atmospheric pressure phase, the rutile type of the tetragonal system, anatase type of the tetragonal system and brookite type of the rhombic system. Among these, the two types of the rutile type and the anatase type are of industrial importance. The above constitution of the present invention has been completed by focusing on the fact that, in these two types of TiO
2
, the rutile type results in smaller temperature variations of specific resistance than the anatase type.
If the content of TiO
2
particles in the resistor composition is less than 0.5 weight %, then the resistor becomes insufficient in load life characteristic. If it exceeds 20 weight %, its noise prevention performance is more likely to deteriorate due t
Honda Toshitaka
Nishikawa Kenichi
Sugimoto Makoto
Tanaka Yutaka
NGK Spark Plug Co. Ltd.
Ramsey Kenneth J.
Snider Ronald R.
Snider & Associates
LandOfFree
Manufacturing method of resistor-incorporated spark plug does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Manufacturing method of resistor-incorporated spark plug, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Manufacturing method of resistor-incorporated spark plug will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2866907