Patent CZ-301907-B6 (CZ)
Title: Spark plug and method of securing mutual position of ceramic insulator body with through central electrode relative to thermally and electrically conducting shell with spark plug side electrode
Inventor: AEALUD PETR
IPC: H01T13/00
Filed: 2006-10-03
Abstract: In the present invention, there is disclosed a spark plug for internal combustion engines, comprising a thermally and electrically conductive metal casing (2) with attachment means, in the cavity of which there is disposed a ceramic insulator (3) with central electrode (5) against which, to create the spark gap of the spark plug, there is arranged a lateral electrode (6) fixed to the casing (2). On the front surface (9) of the outer end of the casing (2) opposite the spark gap, near the edge of its inner opening, there is a radial shoulder (8) adjacent to the corresponding outer shoulder of the insulator (3) in order to fix their mutual positions and their mutual, gas-tight positioning on the opposite, inner end of the casing (2) near the spark gap. In the area of the base of the radial shoulder (8), a radial groove is formed in the front surface (9) of the outer end of the casing (2), making it possible to bend the projection (10) with radial shoulder (8) so formed in the direction of the axis of the spark plug, so that the camber of the bent projection (10) above the front surface (9) of the outer end of the casing (2) is from 0 to 1 mm. The present invention also relates to a method of securing the mutual positioning of the body of the ceramic insulator (3) with through central electrode relative to the thermally and electrically conductive casing (2) with lateral electrode (6) of the spark plug, against the thrust of the body of the ceramic insulator (3) from the cavity of the casing (2) at its outer end, opposite the spark gap, by bending the radial shoulder (8) on the front surface (9) of the casing (2) at its outer end into contact with the outer shoulder of the insulator (3), wherein, on the front surface (9) of the casing (2) at its outer end, a radial shoulder (8) is formed at its inner opening, with at least a slanted outer lateral side, the slanted side is then subjected to pressure from the radial sharp edge of the pressing instrument, whereby the casing is centered with respect to the axis of the ceramic insulator inserted therein and with respect to the pressing instrument, and then pressure is exerted on the radial sharp edge of the pressing instrument until a radial groove is formed in the front surface of the casing, in the area of the base of the radial shoulder, whereby the radial projection of the casing is formed and at the same time, under the pressure of the obliquely shaped part of the radial edge (12) of a pressing tool (11) to thereby centering the casing (2) relative to the axis of the ceramic insulator (3) inserted therein and relative to the forming tool (11). Subsequently, pressure is applied on the radial edge (12) of the pressing tool (11) until a radial groove is formed in the front surface (9) of the casing (2), in the area of the base of the radial shoulder (8), whereby the radial projection (10) of the casing (2) is formed and at the same time, under the pressure of the obliquely shaped part of the radial edge (12) of the pressing tool (11), the downward pressure gradually increases from the outer side on the lateral wall of that projection (10), until that radial projection (10) bends across the shoulder of the ceramic insulator (3) in the direction of its axis to thereby securing the casing (2) against the thrust on that end from the spark plug gap.