Title of Invention

SPARKPLUG FOR AN INTERNAL-COMBUSTION ENGINE

Abstract Sparkplug having a tubular, metallic casing, an insulator, which is held by the casing, and an internal conductor arrangement which is embedded in the insulator, the internal conductor arrangement comprising a connec- tion pin, an erosion resistor, a contact pin and a platinum centre electrode, four earth electrodes being attached to the casing, being bent towards the centre electrode and projecting beyond the insulator by their thickness, and the contact pin being coated and shortened in length in such a way that the erosion resistor pro- trudes forward as far as possible towards the spark gap, and the platinum centre electrode being in the shape of a needle and its rear part having a smaller diameter than the front part, which protrudes out of the insulator. (Figure 1)
Full Text

The invention is based on a sparkplug for inter-nal-combustion engines, as is known already from German Offenlegungsschrift 44 31 143. In this publication, a sparkplug is proposed which has a low degree of wear. In the known sparkplug, a rod-shaped internal conductor is inserted into a cylindrical metal tube which forms the casing, said internal conductor being surrounded by an insulator and having a current-limiting resistor in the circuit of the sparkplug, the current-limiting resistor being arranged in such a way that it protrudes forward, in the direction of the spark gap of the sparkplug, at most as far as the spark gap. Furthermore, in this sparkplug the diameter of the internal conductor is reduced in comparison with conventional sparkplugs, resulting in a reduction in the capacitance of the sparkplug. In this sparkplug according to German Offenlegungsschrift 44 31 143, the electrode head of the internal conductor is also coated with a noble metal layer, and a material which is a good thermal conductor and which simultaneously serves as a heat buffer is provided as the electrode head.
Advantages of the invention
The sparkplug having the features of the main claim has, in comparison With the known art, the advantage that by constructing the electrode in the form of a "needle head11 more wear volume is available. Furthermore,

the reduction in the diameter of the contact pin, the shortening of the length and the forwardly protruding erosion resistor mean that lower mechanical stresses as a result of different coefficients of thermal expansion can occur. Finally, the reduction in the electrode erosion largely avoids ceramic notching. A further advantage is the coating of the contact pin, giving a high degree of resistance to corrosion. Finally, the single or double bending of the earth electrode and the protrusion of the earth electrode beyond the end face of the insulator provide the advantage that this formation of the electrical field enables ceramic breakdowns to be prevented.
The measures specified in the subclaims permit advantageous developments and improvements of the sparkplug specified in the main claim. For example, it is particularly advantageous to dope the platinum electrode. This doping prevents corrosion of the contact pin, since the platinum electrode is sintered gas-tightly into the ceramic. A gas-tight connection of the platinum electrode, the ceramic and the contact pin by means of an active solder also ensures that corrosion of the contact pin is prevented, as is withdrawal of the contact pin. Finally, the contact pin can be replaced by means of an electrically conductive mixture of ceramics/metal, withdrawal of the contact pin likewise being prevented and mechanical stresses being avoided by means of identical coefficients of thermal expansion.

Accordingly, the present invention provides a spark plug naving a tubular, metallic casing with an insulator which is embedded therein and in which a rod-shaped internal conductor arrangement is arranged, the internal conductor arrangement is arranged, the internal conductor arrangement comprising a connection pin, a current-limiting resistor which protrudes forward towards the spark gap, a coated contact pin and a needle-shaped platinum center electrode, the pin-shaped part of the platinum center electrode which is embedded in the insulator having a smaller diameter than the part of the platinum center electrode which protrudes out of the insulator, as well as having two, preferably four earth electrodes which are attached to the casing and which are bent towards the center electrode and which project beyond the end face of the insulator, the amount by which it projects corresponding approximately to the thickness of an earth electrode.
Drawing
Exemplary embodiments of the invention are illustrated in the drawing and explained in more detail in the following description. Figure 1 shows a sparkplug according to the invention in a schematic view; Figure 2 shows the combustion space-side end of the sparkplug according to the invention with earth electrodes which are positioned in a different way.

Description of the exemplary embodiments
The basic design of a sparkplug is already sufficiently known from German Offenlegungsschrift 44 31 143 • Figure 1 shows a schematic, partially sectional view of the inner part of a sparkplug. Here, an insulator 11 is arranged in a metallic, tubular casing 10, the rotationally symmetrical axes of the casing 10 and insulator 11 being situated congruently. Embedded in the insulator 11 is the centre electrode 12, as well as the individual components (which will be explained below) for transmitting the voltage from the connection pin 13 to the centre electrode 12 . In the interior of the insulator 11, the connection pin 13 is connected to the erosion resistor 14. The erosion resistor 14 is connected to the contact pin 15, so that the voltage is transmitted to the centre electrode 12 via the contact pin 15• The centre electrode 12 is composed of platinum and is essentially in the shape of a needle. This means that the rear part of the platinum centre electrode 12 has a substantially smaller diameter than the combustion space-side part of the platinum centre electrode, said part protruding out of the insulator 11. The contact pin 15 itself is coated with an anti-corrosion layer, for example with nickel or with a nickel/silver alloy. Furthermore, in comparison with conventional sparkplugs the contact pin IS is substantially shortened in lexugth. and has a reduced diameter. By shortening the contact pin 15, the erosion resistor is lengthened and made to protrude further in the direction of the spark gap, which has the advantages already described in German Offenlegungsschrif t 44 31 143. The earth electrodes 16 are attached to the basing 10 and bent towards the centre electrode. In the view in this figure, the earth electrodes, of which four are provided here, are bent twice. The earth electrode attached to the casing is initially bent here in the direction of the centre electrode and then bent back in the axial direction a second time so that the end face of the earth electrode points in the axial direction of the sparkplug. The end face of the

earth electrode 16 protects here beyond the end face of the insulator by a prescribable amount. The amount of the projecting length corresponds here approximately to the thickness of an earth electrode.
Figure 2 shows the sparkplug with essentially the same design as in Figure 1. The only difference from Figure 1 is the positioning of the earth electrodes. In Figure 2, the earth electrodes are bent only once, as a result of which the end face of the earth electrode points in the radial direction of the sparkplug. However, here too, the earth electrodes project beyond the front side of the insulator approximately by their thickness. This results in a favourable formation of the electrical field, avoiding ceramic breakdowns.
In addition, the platinum centre electrode can also be coated, this coating being carried out by applying boron, alitrizing, or applying nitrogen or silicon. This coating enables the platinum electrode to be sintered gas-tightly into the ceramic. The connection of the platinum centre electrode, insulator and contact pin by means of a solder likewise contributes to a gas-tight connection, permitting i contact pin corrosion to be avoided and withdrawal of the contact pin to be prevented. The contact pin can finally also be replaced by an electrically conductive ceramic/metal layer.




WE CLAIM:
1. A spark plug having a tubular, metallic casing with an insulator which is
embedded therein and in which a rod-shaped internal conductor arrangement is
arranged, the internal conductor arrangement is arranged, the internal conductor
arrangement comprising a connection pin (13), a current-limiting resistor (14)
which protrudes forward towards the spark gap, a coated contact pin (15) and a
needle-shaped platinum center electrode (12), the pin-shaped part of the
platinum center electrode which is embedded in the insulator having a smaller
diameter than the part of the platinum center electrode which protrudes out of
the insulator, as well as having two, preferably four earth electrodes which are
attached to the casing and which are bent towards the center electrode and
which project beyond the end face of the insulator, the amount by which it
projects corresponding approximately to the thickness of an earth electrode.
2. The spark plug as claimed in claim 1, wherein the earth electrodes are
bent twice, the first bend being directed towards the insulator and the second
bend being bent away from the insulator, so that the end face of the earth
electrode points away from the casing.
3. A spark plug having a tubular, metallic casing, substantially as herein
described with reference to the accompanying drawings.


Documents:

1211-mas-1997 description provisional.pdf

1221-mas-1997- abstract.pdf

1221-mas-1997- claims duplicate.pdf

1221-mas-1997- claims original.pdf

1221-mas-1997- correspondence others.pdf

1221-mas-1997- correspondence po.pdf

1221-mas-1997- description complete duplicate.pdf

1221-mas-1997- description complete original.pdf

1221-mas-1997- drawings.pdf

1221-mas-1997- form 1.pdf

1221-mas-1997- form 26.pdf

1221-mas-1997- form 3.pdf

1221-mas-1997- form 4.pdf

1221-mas-1997- pct.pdf


Patent Number 207649
Indian Patent Application Number 1221/MAS/1997
PG Journal Number 27/2007
Publication Date 06-Jul-2007
Grant Date 19-Jun-2007
Date of Filing 06-Jun-1997
Name of Patentee ROBERT BOSCH GMBH
Applicant Address POSTFACH 30 02 20, D-70442 STUTTGART
Inventors:
# Inventor's Name Inventor's Address
1 ROLAND MUELLER AM SCHLEIFRAIN 23, 71711 STEINHEIM
2 RICHARD ADAMCZUK METZINGER WEG 16,71229 LEONBERG
3 WERNER HERDEN KAPPELWEG 7,70839 GERLINGEN
PCT International Classification Number H01T13/39
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 196 23 989.3 1996-06-15 Germany