Spark plug and method of securing the mutual positioning of the body of the ceramic insulator with through central electrode and the thermally and electrically conductive casing with lateral electrode of the spark plug

Abstract

A spark plug for a combustion engine comprises a thermally and electrically conductive metal casing with attachment means, in the cavity of which there is a ceramic insulator with central electrode against which, to create the spark gap of the spark plug, there is arranged a lateral electrode fixed to the casing. According to a method, the mutual positioning of the body of the ceramic insulator and the thermally and electrically conductive casing with a lateral electrode of the spark plug, against the thrust of the body of the ceramic insulator from the cavity in the casing at its outer end, opposite the spark gap, is secured by bending the radial shoulder on the front surface of the casing at its outer end into contact with the outer shoulder of the insulator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

An example of an embodiment of the spark plug according to this invention is illustrated in the attached drawings.

FIG. 1 shows the whole arrangement of the spark plug in partial cross-section;

FIGS. 2, 3 and 4 illustrate, in time sequence, the procedure for securing the mutual positioning of the body of the ceramic insulator of the spark plug with through central electrode and the thermally and electrically conductive casing with lateral electrode of the spark plug, against the thrust of the body of the ceramic insulator from the cavity in the casing at its outer end.

EXAMPLES OF PREFERRED EMBODIMENTS

The spark plug comprises a thermally and electrically conductive steel casing 2 with attachment means (outer thread 13 of the casing 2 and hexagon 14 for mounting the plug in the engine head). In the cavity of the casing 2 there is a gas-tight ceramic insulator 3 with through central electrode 5 made of AgNi10 alloy. A bent outer lateral electrode 6, made of NiCr2MnSi alloy and connected to the casing 2, fits tightly against the tip of the central electrode 5. The inner shaped opening of the casing 2 has several shoulders and has a seat for positioning the insulator 3 by means of a metal washer 1 (compensating ring) which makes it possible to achieve perfect contact between the casing 2 and the insulator 3, gas-tightness of the spark plug and good transfer of heat from the insulator 3 into the casing 2 and further into the head of the combustion engine. Near its edge, in the area of the threaded pin in the terminal cylindrical end, the opening of the casing 2 is reduced by the inner shoulder.

In the area of the hexagon 14 on the side opposite the spark gap of the spark plug, the casing 2 ends in a surface 9 basically perpendicular to the axis of the casing 2, from which, near the edge of the inner opening of the casing 2, the radial shoulder 8 of the triangular cross-section projects to a height of approximately 0.5 mm. After the casing 2 is placed on the insulator 3 assembly with through central electrode 5 in the assembly jig, the outer end of the casing 2 with radial shoulder 8 fits tightly against the bevelled shoulder of the ceramic insulator 3. The position of the casing 2 with respect to the insulator 3 is defined by the close fit of the inner shoulder of the casing 2, in the area of the tip of the insulator 3 over the metal washer 1 (compensating ring), on the corresponding opposite shoulder of the insulator 3.

In this position the sharp edge 12 of the pressing instrument 11 fits closely against the bevelled surface in the area of the base of the radial shoulder 8 of the casing 2 (FIG. 3), which is thus centred both with regard to the pressing instrument 11 and the ceramic insulator 3 inserted in the casing 2. Then, under pressure, the sharp edge 12 of the pressing instrument 11 penetrates the material of the front surface 9 of the casing 2 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 sharp edge 12 of the pressing instrument 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, whereby the casing 2 is secured against the thrust on that end from the spark plug gap.

Electro-thermal assembly of the casing 2 follows, to ensure the tightness of the connection between the casing 2 and the insulator 3. Part 7 of the wall of the casing 2 is weakened and resistive heating of the casing 2 is carried out by passing an electric current into the casing 2 (in its weakened cross-section). By concurrent pressure in the axial direction between the beveled surface adjacent to the tip of the plug (in the area of the metal washer 1) and the outer part of the casing 2 in the area of the hexagon 14, deformation of the weakened part 7 of the wall of the casing 2 occurs with subsequent definition of the clearance of the spark plug assembly in the axial direction. After the heated, weakened wall of the casing 2 has cooled, the casing contracts in this place (in the axial direction) and the desired assembly bias occurs.

INDUSTRIAL USE

The spark plug according to this invention is designed for ignition combustion engines.

Claims

1. A spark plug for a combustion engine, comprising a thermally and electrically conductive metal casing with attachment means, in the cavity of which there is a ceramic insulator with central electrode against which, to create the spark gap of the spark plug, there is arranged a lateral electrode fixed to the casing where, on the front surface of the outer end of the casing opposite the spark gap, near the edge of its inner opening, there is a radial shoulder adjacent to the corresponding outer shoulder of the insulator in order to fix their mutual positions and their mutual, gas-tight positioning on the opposite, inner end of the casing near the spark gap, characterised in that, in the area of the base of the radial shoulder, a radial groove is formed in the front surface of the outer end of the casing, making it possible to bend the projection with radial shoulder so formed in the direction of the axis of the spark plug, so that the camber of the bent projection above the front surface of the outer end of the casing is from 0 to 1 mm.

2. A spark plug according to claim 1, wherein the radial shoulder has a triangular cross-section about 0.3 to 0.6 mm in height with walls at an angle of 40 to 600, the size of the base being from 0.4 to 1 mm.

3. A spark plug according to claim 1, wherein the casing consists of a single integral part.

4. A method of securing the mutual positioning of the body of the ceramic insulator with through central electrode and the thermally and electrically conductive casing with lateral electrode of the spark plug, against the thrust of the body of the ceramic insulator from the cavity in the casing at its outer end, opposite the spark gap, by bending the radial shoulder on the front surface of the casing at its outer end into contact with the outer shoulder of the insulator, wherein, on the front surface of the casing at its outer end, a radial shoulder 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 sharp edge of the pressing instrument, the downward pressure gradually increases from the outer side on the lateral wall of that projection, until that radial projection bends across the shoulder of the ceramic insulator in the direction of its axis, whereby the casing is secured against the thrust on that end from the spark plug gap.

5. A method according to claim 4, wherein, after bending, the radial projection has a wall about 0.5 to 1 mm in length, ending in a triangular cross-section.