Title of Invention


Abstract "SPARK PLUG FOR INTERNAL COMBUSTION ENGINES" A spark plug is proposed which permits a substantially more compact design of the spark plug, plug connector and cylinder head by reducing the spanner width of the spanner polygon. As a result of lengthening the screw-in thread and the additional provision of a rear, cylindrical projection, the effective clamping-in length can be increased, thus reducing the risk of the spark plug becoming loose.
Full Text

Spark plug for internal combustion engines
Prior art
The invention relates to a spark plug such as is already known in a variety of forms. Such spark plugs have a cylindrical, metallic casing in which there is a central electrode embedded in an insulator, and in which at least one earth electrode is attached to the casing. A thread, with which the spark plug is screwed into the cylinder head, is provided on the outer surface of the casing. In order to tighten the spark plug in the cylinder head, a polygon is formed on the casing, on which polygon a corresponding spanner can be fitted and used to tighten the spark plug in the thread.
Advantages of the invention
The spark plug according to the invention has the advantage that the reduction in the spanner width also permits the external diameter of the spark plug spanner to be reduced, so that the spark plug shaft in the cylinder head can also be made smaller. This produces an overall more compact configuration of the space requirement of spark plug and spark plug spanner in the cylinder head, in which case the insulator geometry can be preserved given a spanner width of 15 mm.
An exemplary embodiment of the invention is illustrated in the drawing and explained in more detail in the

following description. The single figure shows a spark plug in a partially sectional view.
Description of the exemplary embodiment
The spark plug which is illustrated has an essentially tubular metal casing 11 which has a screw-in thread 12 and a spanner polygon 13 on its outside. In the region of its combustion space-side end, the casing 11 has at least one earth elecrode 14, two earth electrodes being illustrated here. The metal casing 11 comprises, in a step-shaped through-hole in a known manner, a rotation-ally symmetrical electrical insulating element 15, which . is essentially composed of aluminium oxide, for exajnple. The insulating element 15 is held in a (^cure^knd sealed fashion in the metal casing 11 and has, m a known manner, a longitudinal hole, into which the connecting bolt 16 is fitted in its connection-side region. On the combustion space-side of the insulating element 15, the central electrode 17 is inserted into a longitudinal hole of the insulating element and is electrically connected to the connecting bolt 16 which is remote from the combustion space, via the longitudinal hole of the insulating element 15. The spark plug is screwed, with its screw-in thread 12, into the cylinder head (not illustrated). In the present spark plug, the combustion space-side section of the metal casing 11 is shaped with the screw-in thread 12 in such a way that the length of the screw-in thread 12 is increased in comparison with conventional spark plugs. Furthermore, the cylindrical metal tube has a cylindrical projection 18. The spanner width of the spanner polygon 13, which in the present case is a dodecahedron, is made smaller than in conventional spark plugs, to 15 mm and less. The cylindrical projection 18, which has no thread, increases the effective clamping-in length and reduces the risk of the spark plug becoming loose. Finally, it is possible to make contact with the high-voltage terminal even within

the ceramics, thus reducing the risk of sparkovers at the insulator head. This also reduces the overall length of the spark plug.
In summary, the shortened design of the spark plug and the smaller spanner width give rise to a more compact unit comprising spark plug, spark plug connector and connection to the cylinder head.

1. A spark plug having a metallic, tubular housing, which has, for installing the spark
plug in an internal combustion engine, a screw-in thread on its outside, for screwing
the spark plug into a cylinder head, and a spanner polygon for tightening the spark
plug in the cylinder head, an essentially rotationally symmetrical insulating element in
a through-hole of the casing being enclosed by the casing in a sealing fashion, and at
least one earth electrode, which is situated opposite, and spaced apart from, a central
electrode held by the insulating element, being arranged at the combustion space-side
end section of the casing, characterized in that a cylindrical projection (18) is provided
between the screw-in thread (12) and the spanner polygon (13) and the spanner width
of the spanner polygon (13) is less than or equal to 15 mm.
2. A spark plug substantially as herein described with reference to the accompanying


1590-mas-1997- abstract.pdf

1590-mas-1997- claims duplicate.pdf

1590-mas-1997- claims original.pdf

1590-mas-1997- correspondence others.pdf

1590-mas-1997- correspondence po.pdf

1590-mas-1997- description complete duplicate.pdf

1590-mas-1997- description complete original.pdf

1590-mas-1997- drawings.pdf

1590-mas-1997- form 1.pdf

1590-mas-1997- form 26.pdf

1590-mas-1997- form 4.pdf

Patent Number 207671
Indian Patent Application Number 1590/MAS/1997
PG Journal Number 27/2007
Publication Date 06-Jul-2007
Grant Date 20-Jun-2007
Date of Filing 15-Jul-1997
Name of Patentee ROBERT BOSCH GMBH
Applicant Address POSTFACH 30 02 20, D-70442 STUTTGART
# Inventor's Name Inventor's Address
PCT International Classification Number G09B19/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 196 36 537.6 1996-09-09 Germany