Electric lamp and discharge devices – Spark plugs – Particular electrode structure or spacing
Patent
1998-02-13
1999-09-14
Patel, Nimeshkumar D.
Electric lamp and discharge devices
Spark plugs
Particular electrode structure or spacing
313136, H01T 1320
Patent
active
059527706
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a spark plug for internal combustion engines.
BACKGROUND INFORMATION
A conventional spark plug is described in German Patent Application No. 44 31 143. It proposes a spark plug which exhibits minimal wear. In the case of the conventional spark plug, a rod-shaped inner conductor is set in a cylindrical metal tube which constitutes the housing, said inner conductor being enclosed in an insulator and having a current-limiting resistor in the electric circuit of the spark plug, said current-limiting resistor being arranged such that it is forward-positioned in the direction of the spark plug's spark gap as close to the spark gap as possible. In addition, in this spark plug, the diameter of the inner conductor is reduced, as compared to conventional spark plugs, as a result of which the capacitance of the spark plug is reduced. In this spark plug, in accordance with German Patent Application No. 44 31 143, the electrode head of the inner conductor is covered with a precious metal coating, and material having good thermal conductivity is used as the electrode head, which also acts as a heat buffer.
SUMMARY OF THE INVENTION
In contrast to a conventional spark plug, a spark plug according to the present invention has the advantage of making available a greater volume that is subject to wear by configuring the electrode in the form of a "nail head." In addition, by reducing the contact pin's diameter and length, and by forward-positioning the burn-off resistor, one can achieve that fewer mechanical stresses caused by different thermal expansion coefficients will occur. By reducing electrode burn-off, nicks in the ceramic can ultimately be substantially avoided. A further advantage lies in the coating of the contact pin, through which means a high corrosion-resistance is achieved. Finally, by configuring the ground electrode in a single or double bend and projecting it beyond the end face of the insulator, the electrical field is so configured that ceramic breakdowns are able to be advantageously prevented.
It is particularly advantageous to dope the platinum electrode. This doping prevents the contact pin from corroding, since the platinum electrode is sintered, gas-tight, into the ceramic. Through the gas-tight bonding of the electrode, the ceramic, and the contact pin using an active solder, the contact pin is also prevented from corroding and from retracting. Ultimately, an electrically conductive ceramic-metal mixture may be substituted for the contact pin, the contact pin likewise being prevented from retracting, and mechanical stresses being avoided as a result of having identical thermal expansion coefficients.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a spark plug according to the present invention.
FIG. 2 shows the combustion-chamber-side end of the spark plug having differently positioned ground electrodes, according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 schematically shows the interior part of a spark plug in a partial cut-away representation. In this context, an insulator 11 is arranged in a metal, tube-shaped housing 10, the rotationally symmetric axes of housing 10 and insulator 11 being coincident. Embedded in insulator 11 is central electrode 12, as well as the individual components described below for transmitting the voltage from connection bolt 13 to central electrode 12. Inside insulator 11, connection bolt 13 is joined to burn-off resistor 14. Burn-off resistor 14 is connected to contact pin 15, so that the voltage is transmitted over contact pin 15 to central electrode 12. Central electrode 12 is made of platinum and essentially has the shape of a nail. This means that the rear part of platinum central electrode 12 has a significantly smaller diameter than the combustion-chamber-side part of the platinum central electrode, which extends out of insulator 11. Contact pin 15 itself is covered with a corrosion-protection coating, e.g., with nickel or with a nickel-silver alloy. In additi
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Patent Abstracts of Japan, vol. 014, No. 002 (E-868), JP 01 251576 A, Oct. 6, 1989.
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Adamczuk Richard
Benedikt Walter
Herde Hans-Dieter
Herden Werner
Klett Dittmar
Patel Nimeshkumar D.
Robert & Bosch GmbH
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