Spark plug having an increased tightening torque

Abstract

A spark plug, including an insulator, a casing including a sealing surface, and a gasket which rests against the sealing surface, the sealing surface including a plurality of recesses.

Claims

1. A spark plug, comprising: an insulator; a casing including a sealing surface; and a gasket which rests against the sealing surface; wherein the sealing surface includes a plurality of recesses, wherein a form-locked connection is present between the recesses and the gasket.

2. The spark plug of claim 1, wherein the recesses are open toward an outer periphery of the casing.

3. The spark plug of claim 1, wherein the sealing surface is provided on the casing at a peripheral projection of the casing.

4. The spark plug of claim 1, wherein the sealing surface is situated at a shell area of the casing provided perpendicularly to an axial direction of the spark plug.

5. The spark plug of claim 1, wherein the recesses are situated at uniform distances in the peripheral direction.

6. The spark plug of claim 1, wherein an outer periphery of the sealing surface corresponds to the greatest diameter of the casing.

7. The spark plug of claim 1, wherein an abrupt transition is provided between the recesses and the sealing surface.

8. The spark plug of claim 1, wherein the number of the recesses is an even number.

9. The spark plug of claim 1, wherein a male thread is provided on the casing as a metric thread M10 or M8.

10. The spark plug of claim 1, wherein the number of the recesses is an even number, in a range from 4 to 10 recesses.

11. The spark plug of claim 1, wherein in an assembled state of the spark plug, the gasket is plastically deformed such that a material of the gasket fills the recesses at least partially.

12. A spark plug, comprising: an insulator; a casing including a sealing surface; and a gasket which rests against the sealing surface; wherein the sealing surface includes a plurality of recesses, and wherein a thickness of the gasket in an axial direction of the spark plug is greater than a depth of the recesses in the axial direction of the spark plug.

13. An internal combustion engine, comprising: a spark plug, including: an insulator; a casing including a sealing surface; and a gasket which rests against the sealing surface; wherein the sealing surface includes a plurality of recesses, wherein a form-locked connection is present between the recesses and the gasket; and a metric M8 thread connection or a metric M10 thread connection between the spark plug and the cylinder head.

14. The internal combustion engine of claim 13, wherein in an assembled state of the spark plug, the gasket is plastically deformed such that a material of the gasket fills the recesses at least partially.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic, partial sectional view of a spark plug according to one exemplary embodiment of the present invention.

(2) FIG. 2 shows a schematic side view of a casing of the spark plug from FIG. 1 including an inserted gasket.

(3) FIG. 3 shows a schematic, perspective view of the casing from FIG. 2 without the gasket.

(4) FIG. 4 shows a schematic sectional view of a casing of the spark plug from FIG. 1.

DETAILED DESCRIPTION

(5) A spark plug 1 according to a first exemplary embodiment of the present invention is described in detail below with reference to FIGS. 1 through 4.

(6) Spark plug 1 includes an insulator 2 which is usually manufactured from a ceramic material. Furthermore, a casing 3 is provided which is provided (manufactured) from a metallic material. Reference numeral 8 identifies a center electrode and reference numeral 9 identifies a ground electrode. FIG. 1 shows the spark plug in section in axial direction X-X.

(7) Spark plug 1 further includes a sealing surface 4 which is provided at casing 3. In this case, sealing surface 4 is oriented perpendicularly to axial direction X-X. Sealing surface 4 is provided at a projection 30 of casing 3. An outer periphery 40 in the area of projection 30 is greater than a diameter of a male thread 41 for the purpose of fixing the spark plug in a cylinder head. Outer periphery 40 provides the largest diameter of casing 3.

(8) As is apparent from FIG. 3 in particular, sealing surface 4 includes a plurality of recesses 5. Eight recesses 5 are provided in this exemplary embodiment. Recesses 5 are arc-shaped and open in the direction of outer periphery 40 (cf. FIGS. 3 and 4). Alternatively, recesses 5 may also be wedge-shaped, wedge-shaped recesses 5 extending from outer periphery 40 in the direction of the longitudinal axis of the spark plug. In this case, the tip of wedge-shaped recess 5 is situated in the direction of the longitudinal axis of the spark plug and the basis of wedge-shaped recess 5 is situated in the direction of outer periphery 40, the basis of wedge-shaped recess 5 being open in the direction of outer periphery 40.

(9) An abrupt transition 7 is provided between recesses 5 and sealing surface 4 in each case. A base area 50 of recesses 5 is in parallel to the area of sealing surfaces 4.

(10) As is further apparent from FIG. 1, spark plug 1 includes a gasket 6. In the assembled state, gasket 6 rests against sealing surface 4. Gasket 6 has a rectangular cross section, in particular a square cross section.

(11) A thickness D of gasket 6 in axial direction X-X of the spark plug is greater than a depth T of recess 5 in axial direction X-X.

(12) The depth of the recesses may be in a range from 0.1 mm to 1 mm.

(13) FIG. 2 shows the state of the spark plug in which gasket 6 lies loosely on sealing surface 4. Here, recesses 5 having depth T are clearly recognizable. When spark plug 1 is screwed into a cylinder head bore (not shown) including a female thread, a plastic deformation of gasket 6 takes place, as soon as gasket 6 lies on a contact surface of the cylinder head, in such a way that gasket 6 fills recesses 5 partially or completely. The open design of recesses 5 toward the radial outer face (cf. FIG. 3) thus allows plastically deformed excess material of gasket 6 to flow out, if necessary.

(14) According to the present invention, a form-locked connection between plastically deformed gasket 6 and recesses 5 is thus achieved during the screwing-in process in addition to the force-fitted connection between sealing surface 4 and gasket 6. This allows for a higher friction coefficient between the gasket and casing 3. The result is a considerably higher resistance to loosening of the spark plug, so that the spark plug, even in the case of a smaller thread diameter of male thread 41, for example M8 or M10 (metric thread DIN 13-1, edition 11.1999), may be fixed in the cylinder head at a high tightening torque without either causing damage to the turns of the thread or even a crack in casing 3.

(15) It should be noted that a sum of all the surfaces of recesses 5 corresponds to approximately 50% of the total surface area of the surface of gasket 6 oriented toward sealing surface 4.

(16) Recesses 5 may be generated with the aid of a shaping process using an appropriately shaped die.

(17) It further may be provided that a surface area of sealing surface 4 and recesses 5 is configured to have a predetermined roughness. In this way, a friction coefficient may be further increased. Advantageously, the friction coefficient is at least 0.25.

(18) According to the present invention, a spark plug may thus be provided for smaller internal combustion engines including a relatively small thread which may be fixed at an increased tightening torque despite the smaller metric thread (for example M8 or M10).